* [PATCH dwarves v3 0/9] pahole: Encode true signatures in kernel BTF
@ 2026-03-20 19:09 Yonghong Song
2026-03-20 19:09 ` [PATCH dwarves v3 1/9] dwarf_loader: Reduce parameter checking with clang DW_AT_calling_convention attr Yonghong Song
` (8 more replies)
0 siblings, 9 replies; 20+ messages in thread
From: Yonghong Song @ 2026-03-20 19:09 UTC (permalink / raw)
To: Alan Maguire, Arnaldo Carvalho de Melo, dwarves
Cc: Alexei Starovoitov, Andrii Nakryiko, bpf, kernel-team
Current vmlinux BTF encoding is based on the source level signatures.
But the compiler may do some optimization and changed the signature.
If the user tried with source level signature, their initial implementation
may have wrong results and then the user need to check what is the
problem and work around it, e.g. through kprobe since kprobe does not
need vmlinux BTF.
Majority of changed signatures are due to dead argument elimination.
The following is a more complex one. The original source signature:
typedef struct {
union {
void *kernel;
void __user *user;
};
bool is_kernel : 1;
} sockptr_t;
typedef sockptr_t bpfptr_t;
static int map_create(union bpf_attr *attr, bpfptr_t uattr) { ... }
After compiler optimization, the signature becomes:
static int map_create(union bpf_attr *attr, bool uattr__is_kernel) { ... }
In the above, uattr__is_kernel corresponds to 'is_kernel' field in sockptr_t.
This makes it easier for developers to understand what changed.
The new signature needs to properly follow ABI specification based on
locations. Otherwise, that signature should be discarded. For example,
0x0242f1f7: DW_TAG_subprogram
DW_AT_name ("memblock_find_in_range")
DW_AT_calling_convention (DW_CC_nocall)
DW_AT_type (0x0242decc "phys_addr_t")
...
0x0242f22e: DW_TAG_formal_parameter
DW_AT_location (indexed (0x14a) loclist = 0x005595bc:
[0xffffffff87a000f9, 0xffffffff87a00178): DW_OP_reg5 RDI
[0xffffffff87a00178, 0xffffffff87a001be): DW_OP_reg14 R14
[0xffffffff87a001be, 0xffffffff87a001c7): DW_OP_entry_value(DW_OP_reg5 RDI), DW_OP_stack_value
[0xffffffff87a001c7, 0xffffffff87a00214): DW_OP_reg14 R14)
DW_AT_name ("start")
DW_AT_type (0x0242decc "phys_addr_t")
...
0x0242f239: DW_TAG_formal_parameter
DW_AT_location (indexed (0x14b) loclist = 0x005595e6:
[0xffffffff87a000f9, 0xffffffff87a00175): DW_OP_reg4 RSI
[0xffffffff87a00175, 0xffffffff87a001b8): DW_OP_reg3 RBX
[0xffffffff87a001b8, 0xffffffff87a001c7): DW_OP_entry_value(DW_OP_reg4 RSI), DW_OP_stack_value
[0xffffffff87a001c7, 0xffffffff87a00214): DW_OP_reg3 RBX)
DW_AT_name ("end")
DW_AT_type (0x0242decc "phys_addr_t")
...
0x0242f245: DW_TAG_formal_parameter
DW_AT_location (indexed (0x14c) loclist = 0x00559610:
[0xffffffff87a001e3, 0xffffffff87a001ef): DW_OP_breg4 RSI+0)
DW_AT_name ("size")
DW_AT_type (0x0242decc "phys_addr_t")
...
0x0242f250: DW_TAG_formal_parameter
DW_AT_const_value (4096)
DW_AT_name ("align")
DW_AT_type (0x0242decc "phys_addr_t")
...
The third argument should correspond to RDX for x86_64. But the location suggests that
the parameter value is stored in the address with 'RSI + 0'. It is not clear whether
the parameter value is stored in RDX or not. So we have to discard this funciton in
vmlinux BTF to avoid incorrect true signatures.
For llvm, any function having
DW_AT_calling_convention (DW_CC_nocall)
in dwarf DW_TAG_subprogram will indicate that this function has signature changed.
I did experiment with latest bpf-next. For x86_64, there are 69103 kernel functions
and 875 kernel functions having signature changed. A series of patches are intended
to ensure true signatures are properly represented. Eventually, only 17 functions
cannot have true signatures due to locations.
For arm64, there are 863 kernel functions having signature changed, and
79 functions cannot have true signatures due to locations. I checked those
functions and look like llvm arm64 backend more relaxed to compute parameter
values.
For full testing, I enabled true signature support in kernel scripts/Makefile.btf like below:
-pahole-flags-$(call test-ge, $(pahole-ver), 130) += --btf_features=attributes
+pahole-flags-$(call test-ge, $(pahole-ver), 130) += --btf_features=attributes --btf_features=+true_signature
For the patch set, Patch 1 introduced usage of DW_AT_calling_convention, which
can precisely identify which function has signature changed. This can filter
majority of functions where their signature won't change.
Patches 2 to 7 tried to find functions with true signature.
Patch 8 enables to btf encoder to properly generate BTF.
Patch 9 includes a few tests.
Changelog:
v2 -> v3:
- v2: https://lore.kernel.org/bpf/20260309153215.1917033-1-yonghong.song@linux.dev/
- Change tests by using newly added test_lib.sh.
- Simplify to get bool variable producer_clang.
- Try to avoid producer_clang appearance in dwarf_loader.c in order to avoid
clear separation between clang and gcc.
v1 -> v2:
- v1: https://lore.kernel.org/bpf/20260305225455.1151066-1-yonghong.song@linux.dev/
- Added producer_clang guarding in btf_encoder. Otherwise, gcc kernel build
will crash pahole.
- Fix an early return in parameter__reg() which didn't do pthread_mutex_unlock()
which caused the deadlock for arm64.
- Add a few more places to guard with producer_clang and conf->true_signature
to maintain the previous behavior if not clang or conf->true_signature is false.
Yonghong Song (9):
dwarf_loader: Reduce parameter checking with clang
DW_AT_calling_convention attr
dwarf_loader: Handle signatures with dead arguments
dwarf_loader: Refactor initial ret -1 to be macro PARM_DEFAULT_FAIL
dwarf_laoder: Handle locations with DW_OP_fbreg
dwarf_loader: Change exprlen checking condition in parameter__reg()
dwarf_loader: Detect optimized parameters with locations having
constant values
dwarf_loader: Handle expression lists
btf_encoder: Handle optimized parameter properly
tests: Add a few clang true signature tests
btf_encoder.c | 13 +-
dwarf_loader.c | 391 ++++++++++++++++++++++++++--
dwarves.h | 2 +
tests/clang_parm_aggregate.sh | 63 +++++
tests/clang_parm_optimized.sh | 77 ++++++
tests/clang_parm_optimized_stack.sh | 77 ++++++
6 files changed, 599 insertions(+), 24 deletions(-)
create mode 100755 tests/clang_parm_aggregate.sh
create mode 100755 tests/clang_parm_optimized.sh
create mode 100755 tests/clang_parm_optimized_stack.sh
--
2.52.0
^ permalink raw reply [flat|nested] 20+ messages in thread
* [PATCH dwarves v3 1/9] dwarf_loader: Reduce parameter checking with clang DW_AT_calling_convention attr
2026-03-20 19:09 [PATCH dwarves v3 0/9] pahole: Encode true signatures in kernel BTF Yonghong Song
@ 2026-03-20 19:09 ` Yonghong Song
2026-03-21 23:10 ` Jiri Olsa
2026-03-20 19:09 ` [PATCH dwarves v3 2/9] dwarf_loader: Handle signatures with dead arguments Yonghong Song
` (7 subsequent siblings)
8 siblings, 1 reply; 20+ messages in thread
From: Yonghong Song @ 2026-03-20 19:09 UTC (permalink / raw)
To: Alan Maguire, Arnaldo Carvalho de Melo, dwarves
Cc: Alexei Starovoitov, Andrii Nakryiko, bpf, kernel-team
Currently every function is checked for its parameters to identify whether
the signature changed or not. If signature indeed changed, pahole may do
some adjustment for parameters for true signatures.
In clang, any function with the following attribute
DW_AT_calling_convention (DW_CC_nocall)
indicates this function having signature changed.
pahole can take advantage of this to avoid parameter checking if
DW_AT_calling_convention is not DW_CC_nocall.
But more importantly, DW_CC_nocall can identify signature-changed functions
and parameters can be checked one-after-another to create the true
signatures. Otherwise, it takes more effort to identify whether a
function has signature changed or not. For example, for funciton
__bpf_kfunc static void bbr_main(struct sock *sk, u32 ack, int flag,
const struct rate_sample *rs) { ... }
and bbr_main() is a callback function in
.cong_control = bbr_main
in 'struct tcp_congestion_ops tcp_bbr_cong_ops'.
In the above bbr_main(...), parameter 'ack' and 'flag' are not used.
The following are some details:
0x0a713b8d: DW_TAG_formal_parameter
DW_AT_location (indexed (0x28) loclist = 0x0166d452:
[0xffffffff83e77fd9, 0xffffffff83e78016): DW_OP_reg5 RDI
...
DW_AT_name ("sk")
DW_AT_type (0x0a6f5b2b "sock *")
...
0x0a713b98: DW_TAG_formal_parameter
DW_AT_name ("ack")
DW_AT_type (0x0a6f58fd "u32")
...
0x0a713ba2: DW_TAG_formal_parameter
DW_AT_name ("flag")
DW_AT_type (0x0a6f57d1 "int")
...
0x0a713bac: DW_TAG_formal_parameter
DW_AT_location (indexed (0x29) loclist = 0x0166d4a8:
[0xffffffff83e77fd9, 0xffffffff83e78016): DW_OP_reg2 RCX
...
DW_AT_name ("rs")
DW_AT_type (0x0a710da5 "const rate_sample *")
DW_AT_decl_line (1027)
Some analysis for the above dwarf can conclude that the 'ark' and 'flag'
may be related to RSI and RDX, considering the last one is RCX. Basically this
requires all parameters are available to collectively decide whether the
true signature can be found or not. In such case, DW_CC_nocall can make things
easier as parameter can be checked one after another.
For a clang built bpf-next kernel, in non-LTO setup, the number of kernel functions
is 69103 and the number of signature changed functions is 875, based on
DW_AT_calling_convention (DW_CC_nocall)
indication.
Among 875 signature changed functions, after this patch, 495 functions
can have proper true signatures, mostly due to simple dead argument
elimination. The number of remaining functions, which cannot get the
true signature, is 379. They will be addressed in the subsequent commits.
In llvm23, I implemented [1] which added DW_CC_nocall for ArgumentPromotion pass.
This compiler pass can add additional DW_CC_nocall cases for the following
compilation:
- Flag -O3 or FullLTO
So once llvm23 available, we may have more DW_CC_nocall cases, hence more
potential true signatures if the kernel is built with -O3 or
with FullLTO (CONFIG_LTO_CLANG_FULL).
[1] https://github.com/llvm/llvm-project/pull/178973
Signed-off-by: Yonghong Song <yonghong.song@linux.dev>
---
dwarf_loader.c | 70 ++++++++++++++++++++++++++++++++++++++++++--------
dwarves.h | 1 +
2 files changed, 60 insertions(+), 11 deletions(-)
diff --git a/dwarf_loader.c b/dwarf_loader.c
index 16fb7be..21f8bf1 100644
--- a/dwarf_loader.c
+++ b/dwarf_loader.c
@@ -1190,6 +1190,10 @@ static ptrdiff_t __dwarf_getlocations(Dwarf_Attribute *attr,
return ret;
}
+struct func_info {
+ bool signature_changed;
+};
+
/* For DW_AT_location 'attr':
* - if first location is DW_OP_regXX with expected number, return the register;
* otherwise save the register for later return
@@ -1252,7 +1256,8 @@ out:
}
static struct parameter *parameter__new(Dwarf_Die *die, struct cu *cu,
- struct conf_load *conf, int param_idx)
+ struct conf_load *conf, int param_idx,
+ struct func_info *info)
{
struct parameter *parm = tag__alloc(cu, sizeof(*parm));
@@ -1263,8 +1268,12 @@ static struct parameter *parameter__new(Dwarf_Die *die, struct cu *cu,
tag__init(&parm->tag, cu, die);
parm->name = attr_string(die, DW_AT_name, conf);
parm->idx = param_idx;
- if (param_idx >= cu->nr_register_params || param_idx < 0)
+ if (param_idx < 0)
return parm;
+ if (!info->signature_changed) {
+ if (cu->producer_clang || param_idx >= cu->nr_register_params)
+ return parm;
+ }
/* Parameters which use DW_AT_abstract_origin to point at
* the original parameter definition (with no name in the DIE)
* are the result of later DWARF generation during compilation
@@ -1337,7 +1346,7 @@ static int formal_parameter_pack__load_params(struct formal_parameter_pack *pack
continue;
}
- struct parameter *param = parameter__new(die, cu, conf, -1);
+ struct parameter *param = parameter__new(die, cu, conf, -1, NULL);
if (param == NULL)
return -1;
@@ -1502,6 +1511,29 @@ static struct ftype *ftype__new(Dwarf_Die *die, struct cu *cu)
return ftype;
}
+static bool function__signature_changed(struct function *func, Dwarf_Die *die)
+{
+ /* The inlined DW_TAG_subprogram typically has the original source type for
+ * abstract origin of a concrete function with address range, inlined subroutine,
+ * or call site.
+ */
+ if (func->inlined)
+ return false;
+
+ if (!func->abstract_origin)
+ return attr_numeric(die, DW_AT_calling_convention) == DW_CC_nocall;
+
+ Dwarf_Attribute attr;
+ if (dwarf_attr(die, DW_AT_abstract_origin, &attr)) {
+ Dwarf_Die origin;
+ if (dwarf_formref_die(&attr, &origin))
+ return attr_numeric(&origin, DW_AT_calling_convention) == DW_CC_nocall;
+ }
+
+ /* This should not happen */
+ return false;
+}
+
static struct function *function__new(Dwarf_Die *die, struct cu *cu, struct conf_load *conf)
{
struct function *func = tag__alloc(cu, sizeof(*func));
@@ -1800,9 +1832,9 @@ static struct tag *die__create_new_parameter(Dwarf_Die *die,
struct ftype *ftype,
struct lexblock *lexblock,
struct cu *cu, struct conf_load *conf,
- int param_idx)
+ int param_idx, struct func_info *info)
{
- struct parameter *parm = parameter__new(die, cu, conf, param_idx);
+ struct parameter *parm = parameter__new(die, cu, conf, param_idx, info);
if (parm == NULL)
return NULL;
@@ -1889,7 +1921,7 @@ static struct tag *die__create_new_subroutine_type(Dwarf_Die *die,
tag__print_not_supported(die);
continue;
case DW_TAG_formal_parameter:
- tag = die__create_new_parameter(die, ftype, NULL, cu, conf, -1);
+ tag = die__create_new_parameter(die, ftype, NULL, cu, conf, -1, NULL);
break;
case DW_TAG_unspecified_parameters:
ftype->unspec_parms = 1;
@@ -2118,7 +2150,8 @@ out_enomem:
}
static int die__process_function(Dwarf_Die *die, struct ftype *ftype,
- struct lexblock *lexblock, struct cu *cu, struct conf_load *conf);
+ struct lexblock *lexblock, struct cu *cu, struct conf_load *conf,
+ struct func_info *info);
static int die__create_new_lexblock(Dwarf_Die *die,
struct cu *cu, struct lexblock *father, struct conf_load *conf)
@@ -2126,7 +2159,7 @@ static int die__create_new_lexblock(Dwarf_Die *die,
struct lexblock *lexblock = lexblock__new(die, cu);
if (lexblock != NULL) {
- if (die__process_function(die, NULL, lexblock, cu, conf) != 0)
+ if (die__process_function(die, NULL, lexblock, cu, conf, NULL) != 0)
goto out_delete;
}
if (father != NULL)
@@ -2246,7 +2279,8 @@ static struct tag *die__create_new_inline_expansion(Dwarf_Die *die,
}
static int die__process_function(Dwarf_Die *die, struct ftype *ftype,
- struct lexblock *lexblock, struct cu *cu, struct conf_load *conf)
+ struct lexblock *lexblock, struct cu *cu, struct conf_load *conf,
+ struct func_info *info)
{
int param_idx = 0;
Dwarf_Die child;
@@ -2320,7 +2354,7 @@ static int die__process_function(Dwarf_Die *die, struct ftype *ftype,
continue;
}
case DW_TAG_formal_parameter:
- tag = die__create_new_parameter(die, ftype, lexblock, cu, conf, param_idx++);
+ tag = die__create_new_parameter(die, ftype, lexblock, cu, conf, param_idx++, info);
break;
case DW_TAG_variable:
tag = die__create_new_variable(die, cu, conf, 0);
@@ -2391,9 +2425,10 @@ out_enomem:
static struct tag *die__create_new_function(Dwarf_Die *die, struct cu *cu, struct conf_load *conf)
{
struct function *function = function__new(die, cu, conf);
+ struct func_info info = { function__signature_changed(function, die) };
if (function != NULL &&
- die__process_function(die, &function->proto, &function->lexblock, cu, conf) != 0) {
+ die__process_function(die, &function->proto, &function->lexblock, cu, conf, &info) != 0) {
function__delete(function, cu);
function = NULL;
}
@@ -3045,6 +3080,17 @@ static unsigned long long dwarf_tag__orig_id(const struct tag *tag,
return cu->extra_dbg_info ? dtag->id : 0;
}
+static bool attr_producer_clang(Dwarf_Die *die)
+{
+ const char *producer;
+
+ producer = attr_string(die, DW_AT_producer, NULL);
+ if (!producer)
+ return false;
+
+ return !!strstr(producer, "clang");
+}
+
struct debug_fmt_ops dwarf__ops;
static int die__process(Dwarf_Die *die, struct cu *cu, struct conf_load *conf)
@@ -3082,6 +3128,7 @@ static int die__process(Dwarf_Die *die, struct cu *cu, struct conf_load *conf)
}
cu->language = attr_numeric(die, DW_AT_language);
+ cu->producer_clang = attr_producer_clang(die);
if (conf->early_cu_filter)
cu = conf->early_cu_filter(cu);
@@ -3841,6 +3888,7 @@ static int cus__merge_and_process_cu(struct cus *cus, struct conf_load *conf,
cu->priv = dcu;
cu->dfops = &dwarf__ops;
cu->language = attr_numeric(cu_die, DW_AT_language);
+ cu->producer_clang = attr_producer_clang(cu_die);
cus__add(cus, cu);
}
diff --git a/dwarves.h b/dwarves.h
index d7c6474..4cabab0 100644
--- a/dwarves.h
+++ b/dwarves.h
@@ -302,6 +302,7 @@ struct cu {
uint8_t has_addr_info:1;
uint8_t uses_global_strings:1;
uint8_t little_endian:1;
+ uint8_t producer_clang:1;
uint8_t nr_register_params;
int register_params[ARCH_MAX_REGISTER_PARAMS];
int functions_saved;
--
2.52.0
^ permalink raw reply related [flat|nested] 20+ messages in thread
* [PATCH dwarves v3 2/9] dwarf_loader: Handle signatures with dead arguments
2026-03-20 19:09 [PATCH dwarves v3 0/9] pahole: Encode true signatures in kernel BTF Yonghong Song
2026-03-20 19:09 ` [PATCH dwarves v3 1/9] dwarf_loader: Reduce parameter checking with clang DW_AT_calling_convention attr Yonghong Song
@ 2026-03-20 19:09 ` Yonghong Song
2026-03-21 23:10 ` Jiri Olsa
2026-03-20 19:09 ` [PATCH dwarves v3 3/9] dwarf_loader: Refactor initial ret -1 to be macro PARM_DEFAULT_FAIL Yonghong Song
` (6 subsequent siblings)
8 siblings, 1 reply; 20+ messages in thread
From: Yonghong Song @ 2026-03-20 19:09 UTC (permalink / raw)
To: Alan Maguire, Arnaldo Carvalho de Melo, dwarves
Cc: Alexei Starovoitov, Andrii Nakryiko, bpf, kernel-team
For llvm dwarf, the dead argument may be in the middle of
DW_TAG_subprogram. So we introduce skip_idx in order to
match expected registers properly.
For example:
0x00042897: DW_TAG_subprogram
DW_AT_name ("create_dev")
DW_AT_calling_convention (DW_CC_nocall)
DW_AT_type (0x0002429a "int")
...
0x000428ab: DW_TAG_formal_parameter
DW_AT_name ("name")
DW_AT_type (0x000242ed "char *")
...
0x000428b5: DW_TAG_formal_parameter
DW_AT_location (indexed (0x3f) loclist = 0x000027f8:
[0xffffffff87681370, 0xffffffff8768137a): DW_OP_reg5 RDI
[0xffffffff8768137a, 0xffffffff87681392): DW_OP_reg3 RBX
[0xffffffff87681392, 0xffffffff876813ae): DW_OP_entry_value(DW_OP_reg5 RDI), DW_OP_stack_value)
DW_AT_name ("dev")
DW_AT_type (0x00026859 "dev_t")
...
With skip_idx, we can identify that the second original argument
'dev' becomes the first one after optimization.
Signed-off-by: Yonghong Song <yonghong.song@linux.dev>
---
dwarf_loader.c | 19 +++++++++++++++++--
1 file changed, 17 insertions(+), 2 deletions(-)
diff --git a/dwarf_loader.c b/dwarf_loader.c
index 21f8bf1..a6e6587 100644
--- a/dwarf_loader.c
+++ b/dwarf_loader.c
@@ -1192,6 +1192,7 @@ static ptrdiff_t __dwarf_getlocations(Dwarf_Attribute *attr,
struct func_info {
bool signature_changed;
+ int skip_idx;
};
/* For DW_AT_location 'attr':
@@ -1264,6 +1265,7 @@ static struct parameter *parameter__new(Dwarf_Die *die, struct cu *cu,
if (parm != NULL) {
bool has_const_value;
Dwarf_Attribute attr;
+ int reg_idx;
tag__init(&parm->tag, cu, die);
parm->name = attr_string(die, DW_AT_name, conf);
@@ -1273,7 +1275,18 @@ static struct parameter *parameter__new(Dwarf_Die *die, struct cu *cu,
if (!info->signature_changed) {
if (cu->producer_clang || param_idx >= cu->nr_register_params)
return parm;
+ } else {
+ /* if true_signature is not enabled, mark parameter as
+ * unexpected_reg since there is a skipped parameter before.
+ */
+ if (!conf->true_signature && info->skip_idx) {
+ parm->unexpected_reg = 1;
+ return parm;
+ }
}
+ reg_idx = param_idx - info->skip_idx;
+ if (reg_idx >= cu->nr_register_params)
+ return parm;
/* Parameters which use DW_AT_abstract_origin to point at
* the original parameter definition (with no name in the DIE)
* are the result of later DWARF generation during compilation
@@ -1311,7 +1324,7 @@ static struct parameter *parameter__new(Dwarf_Die *die, struct cu *cu,
parm->has_loc = dwarf_attr(die, DW_AT_location, &attr) != NULL;
if (parm->has_loc) {
- int expected_reg = cu->register_params[param_idx];
+ int expected_reg = cu->register_params[reg_idx];
int actual_reg = parameter__reg(&attr, expected_reg);
if (actual_reg < 0)
@@ -1324,8 +1337,10 @@ static struct parameter *parameter__new(Dwarf_Die *die, struct cu *cu,
* contents.
*/
parm->unexpected_reg = 1;
- } else if (has_const_value) {
+ } else if (has_const_value || info->signature_changed) {
parm->optimized = 1;
+ if (info->signature_changed)
+ info->skip_idx++;
}
}
--
2.52.0
^ permalink raw reply related [flat|nested] 20+ messages in thread
* [PATCH dwarves v3 3/9] dwarf_loader: Refactor initial ret -1 to be macro PARM_DEFAULT_FAIL
2026-03-20 19:09 [PATCH dwarves v3 0/9] pahole: Encode true signatures in kernel BTF Yonghong Song
2026-03-20 19:09 ` [PATCH dwarves v3 1/9] dwarf_loader: Reduce parameter checking with clang DW_AT_calling_convention attr Yonghong Song
2026-03-20 19:09 ` [PATCH dwarves v3 2/9] dwarf_loader: Handle signatures with dead arguments Yonghong Song
@ 2026-03-20 19:09 ` Yonghong Song
2026-03-20 19:09 ` [PATCH dwarves v3 4/9] dwarf_laoder: Handle locations with DW_OP_fbreg Yonghong Song
` (5 subsequent siblings)
8 siblings, 0 replies; 20+ messages in thread
From: Yonghong Song @ 2026-03-20 19:09 UTC (permalink / raw)
To: Alan Maguire, Arnaldo Carvalho de Melo, dwarves
Cc: Alexei Starovoitov, Andrii Nakryiko, bpf, kernel-team
Later on, More macro return values will be implemented to make
code easier to understand.
Signed-off-by: Yonghong Song <yonghong.song@linux.dev>
---
dwarf_loader.c | 8 +++++---
1 file changed, 5 insertions(+), 3 deletions(-)
diff --git a/dwarf_loader.c b/dwarf_loader.c
index a6e6587..7b3f551 100644
--- a/dwarf_loader.c
+++ b/dwarf_loader.c
@@ -1195,12 +1195,14 @@ struct func_info {
int skip_idx;
};
+#define PARM_DEFAULT_FAIL -1
+
/* For DW_AT_location 'attr':
* - if first location is DW_OP_regXX with expected number, return the register;
* otherwise save the register for later return
* - if location DW_OP_entry_value(DW_OP_regXX) with expected number is in the
* list, return the register; otherwise save register for later return
- * - otherwise if no register was found for locations, return -1.
+ * - otherwise if no register was found for locations, return PARM_DEFAULT_FAIL.
*/
static int parameter__reg(Dwarf_Attribute *attr, int expected_reg)
{
@@ -1210,7 +1212,7 @@ static int parameter__reg(Dwarf_Attribute *attr, int expected_reg)
size_t exprlen, entry_len;
ptrdiff_t offset = 0;
int loc_num = -1;
- int ret = -1;
+ int ret = PARM_DEFAULT_FAIL;
/* use libdw__lock as dwarf_getlocation(s) has concurrency issues
* when libdw is not compiled with experimental --enable-thread-safety
@@ -1327,7 +1329,7 @@ static struct parameter *parameter__new(Dwarf_Die *die, struct cu *cu,
int expected_reg = cu->register_params[reg_idx];
int actual_reg = parameter__reg(&attr, expected_reg);
- if (actual_reg < 0)
+ if (actual_reg == PARM_DEFAULT_FAIL)
parm->optimized = 1;
else if (expected_reg >= 0 && expected_reg != actual_reg)
/* mark parameters that use an unexpected
--
2.52.0
^ permalink raw reply related [flat|nested] 20+ messages in thread
* [PATCH dwarves v3 4/9] dwarf_laoder: Handle locations with DW_OP_fbreg
2026-03-20 19:09 [PATCH dwarves v3 0/9] pahole: Encode true signatures in kernel BTF Yonghong Song
` (2 preceding siblings ...)
2026-03-20 19:09 ` [PATCH dwarves v3 3/9] dwarf_loader: Refactor initial ret -1 to be macro PARM_DEFAULT_FAIL Yonghong Song
@ 2026-03-20 19:09 ` Yonghong Song
2026-03-20 19:09 ` [PATCH dwarves v3 5/9] dwarf_loader: Change exprlen checking condition in parameter__reg() Yonghong Song
` (4 subsequent siblings)
8 siblings, 0 replies; 20+ messages in thread
From: Yonghong Song @ 2026-03-20 19:09 UTC (permalink / raw)
To: Alan Maguire, Arnaldo Carvalho de Melo, dwarves
Cc: Alexei Starovoitov, Andrii Nakryiko, bpf, kernel-team
DW_OP_fbreg means the parameter value will be stored on the
stack. So the corresponding parameter register is not used.
For example:
0x071f7717: DW_TAG_subprogram
DW_AT_name ("jent_health_failure")
DW_AT_calling_convention (DW_CC_nocall)
DW_AT_type (0x071f7626 "unsigned int")
...
0x071f7728: DW_TAG_formal_parameter
DW_AT_location (DW_OP_fbreg -8)
DW_AT_name ("ec")
DW_AT_type (0x071f7ab6 "rand_data *")
...
0x071f7734: NULL
In the above, the parameter 'ec' type is a pointer so it perfectly fits
into a register. But the location uses 'DW_OP_fbreg -8' which prevents
from generating a function with true signatures.
Signed-off-by: Yonghong Song <yonghong.song@linux.dev>
---
dwarf_loader.c | 18 +++++++++++++++---
1 file changed, 15 insertions(+), 3 deletions(-)
diff --git a/dwarf_loader.c b/dwarf_loader.c
index 7b3f551..c259417 100644
--- a/dwarf_loader.c
+++ b/dwarf_loader.c
@@ -1196,6 +1196,7 @@ struct func_info {
};
#define PARM_DEFAULT_FAIL -1
+#define PARM_UNEXPECTED -2
/* For DW_AT_location 'attr':
* - if first location is DW_OP_regXX with expected number, return the register;
@@ -1204,7 +1205,8 @@ struct func_info {
* list, return the register; otherwise save register for later return
* - otherwise if no register was found for locations, return PARM_DEFAULT_FAIL.
*/
-static int parameter__reg(Dwarf_Attribute *attr, int expected_reg)
+static int parameter__reg(Dwarf_Attribute *attr, int expected_reg, struct conf_load *conf,
+ struct func_info *info)
{
Dwarf_Addr base, start, end;
Dwarf_Op *expr, *entry_ops;
@@ -1240,6 +1242,16 @@ static int parameter__reg(Dwarf_Attribute *attr, int expected_reg)
if (ret == expected_reg)
goto out;
break;
+ case DW_OP_fbreg:
+ /* The locaiton like
+ * DW_AT_location (DW_OP_fbreg +<num>)
+ * indicates that the parameter is on the stack. But it is possible
+ * that the parameter can fit in register(s). So conservatively
+ * mark this parameter not suitable for true signatures.
+ */
+ if (info->signature_changed && conf->true_signature)
+ ret = PARM_UNEXPECTED;
+ break;
/* match DW_OP_entry_value(DW_OP_regXX) at any location */
case DW_OP_entry_value:
case DW_OP_GNU_entry_value:
@@ -1327,11 +1339,11 @@ static struct parameter *parameter__new(Dwarf_Die *die, struct cu *cu,
if (parm->has_loc) {
int expected_reg = cu->register_params[reg_idx];
- int actual_reg = parameter__reg(&attr, expected_reg);
+ int actual_reg = parameter__reg(&attr, expected_reg, conf, info);
if (actual_reg == PARM_DEFAULT_FAIL)
parm->optimized = 1;
- else if (expected_reg >= 0 && expected_reg != actual_reg)
+ else if (actual_reg == PARM_UNEXPECTED || (expected_reg >= 0 && expected_reg != actual_reg))
/* mark parameters that use an unexpected
* register to hold a parameter; these will
* be problematic for users of BTF as they
--
2.52.0
^ permalink raw reply related [flat|nested] 20+ messages in thread
* [PATCH dwarves v3 5/9] dwarf_loader: Change exprlen checking condition in parameter__reg()
2026-03-20 19:09 [PATCH dwarves v3 0/9] pahole: Encode true signatures in kernel BTF Yonghong Song
` (3 preceding siblings ...)
2026-03-20 19:09 ` [PATCH dwarves v3 4/9] dwarf_laoder: Handle locations with DW_OP_fbreg Yonghong Song
@ 2026-03-20 19:09 ` Yonghong Song
2026-03-20 19:09 ` [PATCH dwarves v3 6/9] dwarf_loader: Detect optimized parameters with locations having constant values Yonghong Song
` (3 subsequent siblings)
8 siblings, 0 replies; 20+ messages in thread
From: Yonghong Song @ 2026-03-20 19:09 UTC (permalink / raw)
To: Alan Maguire, Arnaldo Carvalho de Melo, dwarves
Cc: Alexei Starovoitov, Andrii Nakryiko, bpf, kernel-team
The change does not change any functionalities. But it allows
DW_OP_stack_value preserved in longer location list for future
parameter checking.
Signed-off-by: Yonghong Song <yonghong.song@linux.dev>
---
dwarf_loader.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/dwarf_loader.c b/dwarf_loader.c
index c259417..117cd49 100644
--- a/dwarf_loader.c
+++ b/dwarf_loader.c
@@ -1227,7 +1227,7 @@ static int parameter__reg(Dwarf_Attribute *attr, int expected_reg, struct conf_l
* DW_OP_stack_value instructs interpreter to pop current value from
* DWARF expression evaluation stack, and thus is not important here.
*/
- if (exprlen > 1 && expr[exprlen - 1].atom == DW_OP_stack_value)
+ if (exprlen == 2 && expr[exprlen - 1].atom == DW_OP_stack_value)
exprlen--;
if (exprlen != 1)
--
2.52.0
^ permalink raw reply related [flat|nested] 20+ messages in thread
* [PATCH dwarves v3 6/9] dwarf_loader: Detect optimized parameters with locations having constant values
2026-03-20 19:09 [PATCH dwarves v3 0/9] pahole: Encode true signatures in kernel BTF Yonghong Song
` (4 preceding siblings ...)
2026-03-20 19:09 ` [PATCH dwarves v3 5/9] dwarf_loader: Change exprlen checking condition in parameter__reg() Yonghong Song
@ 2026-03-20 19:09 ` Yonghong Song
2026-03-20 19:09 ` [PATCH dwarves v3 7/9] dwarf_loader: Handle expression lists Yonghong Song
` (2 subsequent siblings)
8 siblings, 0 replies; 20+ messages in thread
From: Yonghong Song @ 2026-03-20 19:09 UTC (permalink / raw)
To: Alan Maguire, Arnaldo Carvalho de Melo, dwarves
Cc: Alexei Starovoitov, Andrii Nakryiko, bpf, kernel-team
The following is an example:
0x00899a78: DW_TAG_subprogram
DW_AT_low_pc (0xffffffff879be480)
DW_AT_high_pc (0xffffffff879beac4)
DW_AT_frame_base (DW_OP_reg7 RSP)
DW_AT_call_all_calls (true)
DW_AT_name ("split_mem_range")
DW_AT_decl_file ("/home/yhs/work/bpf-next/arch/x86/mm/init.c")
DW_AT_decl_line (401)
DW_AT_prototyped (true)
DW_AT_calling_convention (DW_CC_nocall)
DW_AT_type (0x008861cb "int")
0x00899a8c: DW_TAG_formal_parameter
DW_AT_location (indexed (0x3e) loclist = 0x000b2195:
[0xffffffff879be485, 0xffffffff879be49a): DW_OP_reg5 RDI
[0xffffffff879be49a, 0xffffffff879beac4): DW_OP_breg7 RSP+0)
DW_AT_name ("mr")
DW_AT_decl_file ("/home/yhs/work/bpf-next/arch/x86/mm/init.c")
DW_AT_decl_line (401)
DW_AT_type (0x00899c88 "map_range *")
0x00899a98: DW_TAG_formal_parameter
DW_AT_location (indexed (0x41) loclist = 0x000b21d4:
[0xffffffff879be480, 0xffffffff879be554): DW_OP_consts +0, DW_OP_stack_value
[0xffffffff879be554, 0xffffffff879be56d): DW_OP_consts +1, DW_OP_stack_value
[0xffffffff879be56d, 0xffffffff879be572): DW_OP_reg2 RCX
[0xffffffff879be572, 0xffffffff879be638): DW_OP_breg7 RSP+8
[0xffffffff879be638, 0xffffffff879be63d): DW_OP_reg0 RAX
[0xffffffff879be63d, 0xffffffff879be6ef): DW_OP_breg7 RSP+8
[0xffffffff879be6ef, 0xffffffff879be6f5): DW_OP_reg14 R14
[0xffffffff879be6f5, 0xffffffff879be6fd): DW_OP_breg7 RSP+8
[0xffffffff879be6fd, 0xffffffff879be879): DW_OP_reg14 R14
[0xffffffff879be879, 0xffffffff879be931): DW_OP_reg12 R12
[0xffffffff879be955, 0xffffffff879be961): DW_OP_reg14 R14
[0xffffffff879be961, 0xffffffff879be966): DW_OP_reg12 R12
[0xffffffff879be966, 0xffffffff879be976): DW_OP_reg14 R14
[0xffffffff879be976, 0xffffffff879be9df): DW_OP_reg12 R12
[0xffffffff879be9df, 0xffffffff879be9e5): DW_OP_reg14 R14
[0xffffffff879be9fc, 0xffffffff879bea24): DW_OP_consts +0, DW_OP_stack_value
[0xffffffff879bea24, 0xffffffff879bea74): DW_OP_breg7 RSP+8
[0xffffffff879bea74, 0xffffffff879beac4): DW_OP_reg14 R14)
DW_AT_name ("nr_range")
DW_AT_decl_file ("/home/yhs/work/bpf-next/arch/x86/mm/init.c")
DW_AT_decl_line (401)
DW_AT_type (0x008861cb "int")
0x00899aa4: DW_TAG_formal_parameter
DW_AT_location (indexed (0x3f) loclist = 0x000b21a7:
[0xffffffff879be485, 0xffffffff879be4a4): DW_OP_reg4 RSI
[0xffffffff879be4a4, 0xffffffff879be4e6): DW_OP_reg12 R12
[0xffffffff879be4e6, 0xffffffff879beac4): DW_OP_entry_value(DW_OP_reg4 RSI), DW_OP_stack_value)
DW_AT_name ("start")
DW_AT_decl_file ("/home/yhs/work/bpf-next/arch/x86/mm/init.c")
DW_AT_decl_line (402)
DW_AT_type (0x008861cf "unsigned long")
0x00899ab0: DW_TAG_formal_parameter
DW_AT_location (indexed (0x40) loclist = 0x000b21c2:
[0xffffffff879be485, 0xffffffff879be4a9): DW_OP_reg1 RDX
[0xffffffff879be4a9, 0xffffffff879beac4): DW_OP_breg7 RSP+32)
DW_AT_name ("end")
DW_AT_decl_file ("/home/yhs/work/bpf-next/arch/x86/mm/init.c")
DW_AT_decl_line (403)
DW_AT_type (0x008861cf "unsigned long")
The parameter 'nr_range' is a constant and won't consume any ABI register.
Signed-off-by: Yonghong Song <yonghong.song@linux.dev>
---
dwarf_loader.c | 46 ++++++++++++++++++++++++++++++++++++++++++----
1 file changed, 42 insertions(+), 4 deletions(-)
diff --git a/dwarf_loader.c b/dwarf_loader.c
index 117cd49..e10e5d8 100644
--- a/dwarf_loader.c
+++ b/dwarf_loader.c
@@ -1197,6 +1197,21 @@ struct func_info {
#define PARM_DEFAULT_FAIL -1
#define PARM_UNEXPECTED -2
+#define PARM_OPTIMIZED_OUT -3
+#define PARM_CONTINUE -4
+
+static int parameter__multi_exprs(Dwarf_Op *expr, int loc_num) {
+ switch (expr[0].atom) {
+ case DW_OP_lit0 ... DW_OP_lit31:
+ case DW_OP_constu:
+ case DW_OP_consts:
+ if (loc_num != 0)
+ break;
+ return PARM_OPTIMIZED_OUT;
+ }
+
+ return PARM_CONTINUE;
+}
/* For DW_AT_location 'attr':
* - if first location is DW_OP_regXX with expected number, return the register;
@@ -1230,8 +1245,17 @@ static int parameter__reg(Dwarf_Attribute *attr, int expected_reg, struct conf_l
if (exprlen == 2 && expr[exprlen - 1].atom == DW_OP_stack_value)
exprlen--;
- if (exprlen != 1)
- continue;
+ if (exprlen != 1) {
+ if (!info->signature_changed || !conf->true_signature)
+ continue;
+
+ int res;
+ res = parameter__multi_exprs(expr, loc_num);
+ if (res == PARM_CONTINUE)
+ continue;
+ ret = res;
+ goto out;
+ }
switch (expr->atom) {
/* match DW_OP_regXX at first location */
@@ -1252,6 +1276,16 @@ static int parameter__reg(Dwarf_Attribute *attr, int expected_reg, struct conf_l
if (info->signature_changed && conf->true_signature)
ret = PARM_UNEXPECTED;
break;
+ case DW_OP_lit0 ... DW_OP_lit31:
+ case DW_OP_constu:
+ case DW_OP_consts:
+ if (info->signature_changed && conf->true_signature) {
+ if (loc_num != 0)
+ break;
+ ret = PARM_OPTIMIZED_OUT;
+ goto out;
+ }
+ break;
/* match DW_OP_entry_value(DW_OP_regXX) at any location */
case DW_OP_entry_value:
case DW_OP_GNU_entry_value:
@@ -1341,9 +1375,12 @@ static struct parameter *parameter__new(Dwarf_Die *die, struct cu *cu,
int expected_reg = cu->register_params[reg_idx];
int actual_reg = parameter__reg(&attr, expected_reg, conf, info);
- if (actual_reg == PARM_DEFAULT_FAIL)
+ if (actual_reg == PARM_DEFAULT_FAIL) {
+ parm->optimized = 1;
+ } else if (actual_reg == PARM_OPTIMIZED_OUT) {
parm->optimized = 1;
- else if (actual_reg == PARM_UNEXPECTED || (expected_reg >= 0 && expected_reg != actual_reg))
+ info->skip_idx++;
+ } else if (actual_reg == PARM_UNEXPECTED || (expected_reg >= 0 && expected_reg != actual_reg)) {
/* mark parameters that use an unexpected
* register to hold a parameter; these will
* be problematic for users of BTF as they
@@ -1351,6 +1388,7 @@ static struct parameter *parameter__new(Dwarf_Die *die, struct cu *cu,
* contents.
*/
parm->unexpected_reg = 1;
+ }
} else if (has_const_value || info->signature_changed) {
parm->optimized = 1;
if (info->signature_changed)
--
2.52.0
^ permalink raw reply related [flat|nested] 20+ messages in thread
* [PATCH dwarves v3 7/9] dwarf_loader: Handle expression lists
2026-03-20 19:09 [PATCH dwarves v3 0/9] pahole: Encode true signatures in kernel BTF Yonghong Song
` (5 preceding siblings ...)
2026-03-20 19:09 ` [PATCH dwarves v3 6/9] dwarf_loader: Detect optimized parameters with locations having constant values Yonghong Song
@ 2026-03-20 19:09 ` Yonghong Song
2026-03-21 23:10 ` Jiri Olsa
2026-03-20 19:09 ` [PATCH dwarves v3 8/9] btf_encoder: Handle optimized parameter properly Yonghong Song
2026-03-20 19:10 ` [PATCH dwarves v3 9/9] tests: Add a few clang true signature tests Yonghong Song
8 siblings, 1 reply; 20+ messages in thread
From: Yonghong Song @ 2026-03-20 19:09 UTC (permalink / raw)
To: Alan Maguire, Arnaldo Carvalho de Melo, dwarves
Cc: Alexei Starovoitov, Andrii Nakryiko, bpf, kernel-team
The corresponding type is checked for the parameter.
If the parameter size is less or equal to size of long,
the argument should match the corresponding ABI register.
For example:
0x0aba0808: DW_TAG_subprogram
DW_AT_name ("addrconf_ifdown")
DW_AT_calling_convention (DW_CC_nocall)
DW_AT_type (0x0ab7d8e9 "int")
...
0x0aba082b: DW_TAG_formal_parameter
DW_AT_location (indexed (0x32b) loclist = 0x016eabcd:
[0xffffffff83f6fef9, 0xffffffff83f6ff98): DW_OP_reg5 RDI
[0xffffffff83f6ff98, 0xffffffff83f70080): DW_OP_reg12 R12
[0xffffffff83f70080, 0xffffffff83f70111): DW_OP_breg7 RSP+112
[0xffffffff83f70111, 0xffffffff83f7014f): DW_OP_reg12 R12
[0xffffffff83f7014f, 0xffffffff83f7123c): DW_OP_breg7 RSP+112
[0xffffffff83f7123c, 0xffffffff83f7128c): DW_OP_entry_value(DW_OP_reg5 RDI), DW_OP_stack_value
[0xffffffff83f7128c, 0xffffffff83f712a9): DW_OP_reg12 R12
[0xffffffff83f712a9, 0xffffffff83f712cd): DW_OP_breg7 RSP+112
[0xffffffff83f712cd, 0xffffffff83f712d2): DW_OP_entry_value(DW_OP_reg5 RDI), DW_OP_stack_value
[0xffffffff83f712d2, 0xffffffff83f713dd): DW_OP_breg7 RSP+112)
DW_AT_name ("dev")
DW_AT_type (0x0ab7cb7d "net_device *")
...
0x0aba0836: DW_TAG_formal_parameter
DW_AT_location (indexed (0x32c) loclist = 0x016eac39:
[0xffffffff83f6fef9, 0xffffffff83f6ff15): DW_OP_breg4 RSI+0, DW_OP_constu 0xffffffff, DW_OP_and, DW_OP_convert (0x0ab7b571) "DW_ATE_unsigned_1", DW_OP_convert (0x0ab7b576) "DW_ATE_unsigned_8", DW_OP_stack_value
[0xffffffff83f6ff15, 0xffffffff83f7127c): DW_OP_breg7 RSP+36, DW_OP_deref_size 0x4, DW_OP_convert (0x0ab7b571) "DW_ATE_unsigned_1", DW_OP_convert (0x0ab7b576) "DW_ATE_unsigned_8", DW_OP_stack_value
[0xffffffff83f7128c, 0xffffffff83f713dd): DW_OP_breg7 RSP+36, DW_OP_deref_size 0x4, DW_OP_convert (0x0ab7b571) "DW_ATE_unsigned_1", DW_OP_convert (0x0ab7b576) "DW_ATE_unsigned_8", DW_OP_stack_value)
DW_AT_name ("unregister")
DW_AT_type (0x0ab7c933 "bool")
...
The parameter 'unregister' is the second argument which matches ABI register RSI.
So the function "addrconf_ifdown" signature is valid.
If the parameter size is '2 x size_of_long', more handling is necessary, e.g., below:
0x0a01e174: DW_TAG_subprogram
DW_AT_name ("check_zeroed_sockptr")
DW_AT_calling_convention (DW_CC_nocall)
DW_AT_type (0x09fead35 "int")
...
0x0a01e187: DW_TAG_formal_parameter
DW_AT_location (indexed (0x5b6) loclist = 0x0157f03f:
[0xffffffff83c941c0, 0xffffffff83c941c4): DW_OP_reg5 RDI, DW_OP_piece 0x8, DW_OP_reg4 RSI, DW_OP_piece 0x1
[0xffffffff83c941c4, 0xffffffff83c941cc): DW_OP_piece 0x8, DW_OP_reg4 RSI, DW_OP_piece 0x1
[0xffffffff83c941e1, 0xffffffff83c941e4): DW_OP_piece 0x8, DW_OP_reg4 RSI, DW_OP_piece 0x1)
DW_AT_name ("src")
DW_AT_type (0x09ff832d "sockptr_t")
...
0x0a01e193: DW_TAG_formal_parameter
DW_AT_const_value (64)
DW_AT_name ("offset")
DW_AT_type (0x09fee984 "size_t")
...
0x0a01e19e: DW_TAG_formal_parameter
DW_AT_location (indexed (0x5b7) loclist = 0x0157f06b:
[0xffffffff83c941c0, 0xffffffff83c941d1): DW_OP_reg1 RDX
[0xffffffff83c941d1, 0xffffffff83c941e1): DW_OP_entry_value(DW_OP_reg1 RDX), DW_OP_stack_value
[0xffffffff83c941e1, 0xffffffff83c941e9): DW_OP_reg1 RDX)
DW_AT_name ("size")
DW_AT_type (0x09fee984 "size_t")
...
The first parameter 'src' will take two ABI registers. This patch correctly detects such a pattern
to construct the true signature.
However, it is possible that only one 'size_of_long' is used from '2 x size_of_long'. For example
0x019520c6: DW_TAG_subprogram
DW_AT_name ("map_create")
DW_AT_calling_convention (DW_CC_nocall)
DW_AT_type (0x01934b29 "int")
...
0x01952111: DW_TAG_formal_parameter
DW_AT_location (indexed (0x31b) loclist = 0x0034fa0f:
[0xffffffff81892345, 0xffffffff8189237c): DW_OP_reg5 RDI
[0xffffffff8189237c, 0xffffffff818923bd): DW_OP_reg3 RBX
[0xffffffff818923bd, 0xffffffff818923d4): DW_OP_entry_value(DW_OP_reg5 RDI), DW_OP_stack_value
[0xffffffff818923d4, 0xffffffff81892dcb): DW_OP_reg3 RBX
[0xffffffff81892df3, 0xffffffff81892e01): DW_OP_entry_value(DW_OP_reg5 RDI), DW_OP_stack_value
[0xffffffff81892e01, 0xffffffff818932a9): DW_OP_reg3 RBX)
DW_AT_name ("attr")
DW_AT_type (0x01934d17 "bpf_attr *")
...
0x0195211d: DW_TAG_formal_parameter
DW_AT_location (indexed (0x31a) loclist = 0x0034f9dc:
[0xffffffff81892345, 0xffffffff81892357): DW_OP_piece 0x8, DW_OP_reg4 RSI, DW_OP_piece 0x1
[0xffffffff81892357, 0xffffffff81892f02): DW_OP_piece 0x8, DW_OP_breg7 RSP+20, DW_OP_deref_size 0x4, DW_OP_stack_value, DW_OP_piece 0x1
[0xffffffff81892f07, 0xffffffff818932a9): DW_OP_piece 0x8, DW_OP_breg7 RSP+20, DW_OP_deref_size 0x4, DW_OP_stack_value, DW_OP_piece 0x1)
DW_AT_name ("uattr")
DW_AT_type (0x019512ab "bpfptr_t")
...
For parameter 'uattr', only second half of parameter is used. For such cases,
the name and the type is changed in pahole and eventually going to vmlinux btf.
[55697] FUNC_PROTO '(anon)' ret_type_id=106780 vlen=2
'attr' type_id=455
'uattr__is_kernel' type_id=82014
[82014] TYPEDEF 'bool' type_id=67434
[113251] FUNC 'map_create' type_id=55697 linkage=static
You can see the new parameter name is 'uattr__is_kernel' and the type is 'bool'.
This makes thing easier for users to get the true signature.
Signed-off-by: Yonghong Song <yonghong.song@linux.dev>
---
dwarf_loader.c | 246 +++++++++++++++++++++++++++++++++++++++++++++++--
dwarves.h | 1 +
2 files changed, 240 insertions(+), 7 deletions(-)
diff --git a/dwarf_loader.c b/dwarf_loader.c
index e10e5d8..7d23c7d 100644
--- a/dwarf_loader.c
+++ b/dwarf_loader.c
@@ -1100,6 +1100,16 @@ static void arch__set_register_params(const GElf_Ehdr *ehdr, struct cu *cu)
}
}
+static bool arch__agg_use_two_regs(const GElf_Ehdr *ehdr)
+{
+ switch (ehdr->e_machine) {
+ case EM_S390:
+ return false;
+ default:
+ return true;
+ }
+}
+
static struct template_type_param *template_type_param__new(Dwarf_Die *die, struct cu *cu, struct conf_load *conf)
{
struct template_type_param *ttparm = tag__alloc(cu, sizeof(*ttparm));
@@ -1199,8 +1209,98 @@ struct func_info {
#define PARM_UNEXPECTED -2
#define PARM_OPTIMIZED_OUT -3
#define PARM_CONTINUE -4
+#define PARM_TWO_ADDR_LEN -5
+#define PARM_TO_BE_IMPROVED -6
+
+static int __get_type_byte_size(Dwarf_Die *die, struct cu *cu) {
+ Dwarf_Attribute attr;
+ if (dwarf_attr(die, DW_AT_type, &attr) == NULL)
+ return 0;
-static int parameter__multi_exprs(Dwarf_Op *expr, int loc_num) {
+ Dwarf_Die type_die;
+ if (dwarf_formref_die(&attr, &type_die) == NULL)
+ return 0;
+
+ /* A type does not have byte_size.
+ * 0x000dac83: DW_TAG_formal_parameter
+ DW_AT_location (indexed (0x385) loclist = 0x00016175:
+ [0xffff800080098cb0, 0xffff800080098cb4): DW_OP_breg8 W8+0
+ [0xffff800080098cb4, 0xffff800080098ff4): DW_OP_breg31 WSP+16, DW_OP_deref
+ [0xffff800080099054, 0xffff80008009908c): DW_OP_breg31 WSP+16, DW_OP_deref)
+ DW_AT_name ("ubuf")
+ DW_AT_decl_file ("/home/yhs/work/bpf-next/arch/arm64/kernel/ptrace.c")
+ DW_AT_decl_line (886)
+ DW_AT_type (0x000d467e "const void *")
+
+ * 0x000d467e: DW_TAG_pointer_type
+ DW_AT_type (0x000c4320 "const void")
+
+ * 0x000c4320: DW_TAG_const_type
+ */
+ if (dwarf_tag(&type_die) == DW_TAG_pointer_type)
+ return cu->addr_size;
+
+ uint64_t bsize = attr_numeric(&type_die, DW_AT_byte_size);
+ if (bsize == 0)
+ return __get_type_byte_size(&type_die, cu);
+
+ return bsize;
+}
+
+static int get_type_byte_size(Dwarf_Die *die, struct cu *cu) {
+ int byte_size = 0;
+
+ Dwarf_Attribute attr;
+ if (dwarf_attr(die, DW_AT_abstract_origin, &attr)) {
+ Dwarf_Die origin;
+ if (dwarf_formref_die(&attr, &origin))
+ byte_size = __get_type_byte_size(&origin, cu);
+ } else {
+ byte_size = __get_type_byte_size(die, cu);
+ }
+ return byte_size;
+}
+
+/* Traverse the parameter type until finding the member type which has expected
+ * struct type offset.
+*/
+static Dwarf_Die *get_member_with_offset(Dwarf_Die *die, int offset, Dwarf_Die *member_die) {
+ Dwarf_Attribute attr;
+ if (dwarf_attr(die, DW_AT_type, &attr) == NULL)
+ return NULL;
+
+ Dwarf_Die type_die;
+ if (dwarf_formref_die(&attr, &type_die) == NULL)
+ return NULL;
+
+ uint64_t bsize = attr_numeric(&type_die, DW_AT_byte_size);
+ if (bsize == 0)
+ return get_member_with_offset(&type_die, offset, member_die);
+
+ if (dwarf_tag(&type_die) != DW_TAG_structure_type)
+ return NULL;
+
+ if (!dwarf_haschildren(&type_die) || dwarf_child(&type_die, member_die) != 0)
+ return NULL;
+ do {
+ if (dwarf_tag(member_die) != DW_TAG_member)
+ continue;
+
+ int off = attr_numeric(member_die, DW_AT_data_bit_offset);
+ if (off == offset * 8)
+ return member_die;
+ } while (dwarf_siblingof(member_die, member_die) == 0);
+
+ return NULL;
+}
+
+/* For two address length case, lower_half and upper_half represents the parameter.
+ * The lower_half and upper_half accumulates field information across possible multiple
+ * location lists.
+ */
+static int parameter__multi_exprs(Dwarf_Op *expr, int loc_num, struct cu *cu, size_t exprlen,
+ Dwarf_Die *die, int expected_reg, int byte_size,
+ unsigned long *lower_half, unsigned long *upper_half, int *ret) {
switch (expr[0].atom) {
case DW_OP_lit0 ... DW_OP_lit31:
case DW_OP_constu:
@@ -1210,9 +1310,119 @@ static int parameter__multi_exprs(Dwarf_Op *expr, int loc_num) {
return PARM_OPTIMIZED_OUT;
}
+ if (byte_size <= cu->addr_size || !cu->agg_use_two_regs) {
+ switch (expr[0].atom) {
+ case DW_OP_reg0 ... DW_OP_reg31:
+ if (loc_num != 0)
+ break;
+ *ret = expr[0].atom;
+ if (*ret == expected_reg)
+ return *ret;
+ break;
+ case DW_OP_breg0 ... DW_OP_breg31:
+ if (loc_num != 0)
+ break;
+ bool has_op_stack_value = false;
+ for (int i = 1; i < exprlen; i++) {
+ if (expr[i].atom == DW_OP_stack_value) {
+ has_op_stack_value = true;
+ break;
+ }
+ }
+ if (!has_op_stack_value)
+ break;
+ /* The existence of DW_OP_stack_value means that
+ * DW_OP_bregX register is used as value.
+ */
+ *ret = expr[0].atom - DW_OP_breg0 + DW_OP_reg0;
+ if (*ret == expected_reg)
+ return *ret;
+ }
+ } else {
+ /* cu->addr * 2 */
+ int off = 0;
+ for (int i = 0; i < exprlen; i++) {
+ if (expr[i].atom == DW_OP_piece) {
+ int num = expr[i].number;
+ if (i == 0) {
+ off = num;
+ continue;
+ }
+ if (off < cu->addr_size) (*lower_half) |= (1 << off);
+ else (*upper_half) |= (1 << (off - cu->addr_size));
+ off += num;
+ } else if (expr[i].atom >= DW_OP_reg0 && expr[i].atom <= DW_OP_reg31) {
+ if (off < cu->addr_size)
+ *ret = expr[i].atom;
+ else if (*ret < 0)
+ *ret = expr[i].atom;
+ }
+ /* FIXME: not handling DW_OP_bregX yet since we do not have
+ * a use case for it yet for linux kernel.
+ */
+ }
+ }
+
return PARM_CONTINUE;
}
+/* The lower_half and upper_half, computed in parameter__multi_exprs(), are handled here.
+ */
+static int parameter__handle_two_addr_len(int expected_reg, unsigned long lower_half, unsigned long upper_half,
+ int ret, Dwarf_Die *die, struct conf_load *conf, struct cu *cu,
+ struct parameter *parm) {
+ if (!lower_half && !upper_half)
+ return ret;
+
+ if (ret != expected_reg)
+ return ret;
+
+ if (!conf->true_signature)
+ return PARM_DEFAULT_FAIL;
+
+ /* Both halfs are used based on dwarf */
+ if (lower_half && upper_half)
+ return PARM_TWO_ADDR_LEN;
+
+ /* FIXME: parm->name may be NULL due to abstract origin. We do not want to
+ * update abstract origin as the type in abstract origin may be used
+ * in some other places. We could remove abstract origin in this parameter
+ * and add name and type in parameter itself. Right now, for current bpf-next
+ * repo, we do not have instances below where parm->name is NULL for x86_64 arch.
+ */
+ if (!parm->name)
+ return PARM_TO_BE_IMPROVED;
+
+ /* FIXME: Only support single field now so we can have a good parameter name and
+ * type for it.
+ */
+ if (__builtin_popcountll(lower_half) >= 2 || __builtin_popcountll(upper_half) >= 2)
+ return PARM_TO_BE_IMPROVED;
+
+ int field_offset;
+ if (__builtin_popcountll(lower_half) == 1)
+ field_offset = __builtin_ctzll(lower_half);
+ else
+ field_offset = cu->addr_size + __builtin_ctzll(upper_half);
+
+ /* FIXME: Only struct type is supported. */
+ Dwarf_Die member_die;
+ if (!get_member_with_offset(die, field_offset, &member_die))
+ return PARM_TO_BE_IMPROVED;
+
+ const char *member_name = attr_string(&member_die, DW_AT_name, conf);
+ int len = sizeof(parm->name) + strlen(member_name) + 3;
+ char *new_name = malloc(len);
+ sprintf(new_name, "%s__%s", parm->name, member_name);
+ parm->name = new_name;
+
+ struct tag *tag = &parm->tag;
+ struct dwarf_tag *dtag = tag__dwarf(tag);
+ dwarf_tag__set_attr_type(dtag, type, &member_die, DW_AT_type);
+
+ return ret;
+}
+
/* For DW_AT_location 'attr':
* - if first location is DW_OP_regXX with expected number, return the register;
* otherwise save the register for later return
@@ -1221,15 +1431,18 @@ static int parameter__multi_exprs(Dwarf_Op *expr, int loc_num) {
* - otherwise if no register was found for locations, return PARM_DEFAULT_FAIL.
*/
static int parameter__reg(Dwarf_Attribute *attr, int expected_reg, struct conf_load *conf,
- struct func_info *info)
+ struct func_info *info, struct cu *cu, Dwarf_Die *die,
+ struct parameter *parm)
{
Dwarf_Addr base, start, end;
Dwarf_Op *expr, *entry_ops;
Dwarf_Attribute entry_attr;
size_t exprlen, entry_len;
ptrdiff_t offset = 0;
+ int byte_size = 0;
int loc_num = -1;
int ret = PARM_DEFAULT_FAIL;
+ unsigned long lower_half = 0, upper_half = 0;
/* use libdw__lock as dwarf_getlocation(s) has concurrency issues
* when libdw is not compiled with experimental --enable-thread-safety
@@ -1249,8 +1462,17 @@ static int parameter__reg(Dwarf_Attribute *attr, int expected_reg, struct conf_l
if (!info->signature_changed || !conf->true_signature)
continue;
+ if (!byte_size)
+ byte_size = get_type_byte_size(die, cu);
+ /* This should not happen. */
+ if (!byte_size) {
+ ret = PARM_UNEXPECTED;
+ goto out;
+ }
+
int res;
- res = parameter__multi_exprs(expr, loc_num);
+ res = parameter__multi_exprs(expr, loc_num, cu, exprlen, die, expected_reg,
+ byte_size, &lower_half, &upper_half, &ret);
if (res == PARM_CONTINUE)
continue;
ret = res;
@@ -1299,6 +1521,10 @@ static int parameter__reg(Dwarf_Attribute *attr, int expected_reg, struct conf_l
break;
}
}
+
+ ret = parameter__handle_two_addr_len(expected_reg, lower_half, upper_half,
+ ret, die, conf, cu, parm);
+
out:
pthread_mutex_unlock(&libdw__lock);
return ret;
@@ -1333,8 +1559,6 @@ static struct parameter *parameter__new(Dwarf_Die *die, struct cu *cu,
}
}
reg_idx = param_idx - info->skip_idx;
- if (reg_idx >= cu->nr_register_params)
- return parm;
/* Parameters which use DW_AT_abstract_origin to point at
* the original parameter definition (with no name in the DIE)
* are the result of later DWARF generation during compilation
@@ -1372,15 +1596,22 @@ static struct parameter *parameter__new(Dwarf_Die *die, struct cu *cu,
parm->has_loc = dwarf_attr(die, DW_AT_location, &attr) != NULL;
if (parm->has_loc) {
+ if (reg_idx >= cu->nr_register_params)
+ return parm;
+
int expected_reg = cu->register_params[reg_idx];
- int actual_reg = parameter__reg(&attr, expected_reg, conf, info);
+ int actual_reg = parameter__reg(&attr, expected_reg, conf, info, cu, die, parm);
if (actual_reg == PARM_DEFAULT_FAIL) {
parm->optimized = 1;
} else if (actual_reg == PARM_OPTIMIZED_OUT) {
parm->optimized = 1;
info->skip_idx++;
- } else if (actual_reg == PARM_UNEXPECTED || (expected_reg >= 0 && expected_reg != actual_reg)) {
+ } else if (actual_reg == PARM_TWO_ADDR_LEN) {
+ /* account for parameter with two registers */
+ info->skip_idx--;
+ } else if (actual_reg == PARM_UNEXPECTED || actual_reg == PARM_TO_BE_IMPROVED ||
+ (expected_reg >= 0 && expected_reg != actual_reg)) {
/* mark parameters that use an unexpected
* register to hold a parameter; these will
* be problematic for users of BTF as they
@@ -3414,6 +3645,7 @@ static int cu__set_common(struct cu *cu, struct conf_load *conf,
cu->little_endian = ehdr.e_ident[EI_DATA] == ELFDATA2LSB;
cu->nr_register_params = arch__nr_register_params(&ehdr);
+ cu->agg_use_two_regs = arch__agg_use_two_regs(&ehdr);
arch__set_register_params(&ehdr, cu);
return 0;
}
diff --git a/dwarves.h b/dwarves.h
index 4cabab0..28792b5 100644
--- a/dwarves.h
+++ b/dwarves.h
@@ -303,6 +303,7 @@ struct cu {
uint8_t uses_global_strings:1;
uint8_t little_endian:1;
uint8_t producer_clang:1;
+ uint8_t agg_use_two_regs:1; /* An aggregate like {long a; long b;} */
uint8_t nr_register_params;
int register_params[ARCH_MAX_REGISTER_PARAMS];
int functions_saved;
--
2.52.0
^ permalink raw reply related [flat|nested] 20+ messages in thread
* [PATCH dwarves v3 8/9] btf_encoder: Handle optimized parameter properly
2026-03-20 19:09 [PATCH dwarves v3 0/9] pahole: Encode true signatures in kernel BTF Yonghong Song
` (6 preceding siblings ...)
2026-03-20 19:09 ` [PATCH dwarves v3 7/9] dwarf_loader: Handle expression lists Yonghong Song
@ 2026-03-20 19:09 ` Yonghong Song
2026-03-20 19:10 ` [PATCH dwarves v3 9/9] tests: Add a few clang true signature tests Yonghong Song
8 siblings, 0 replies; 20+ messages in thread
From: Yonghong Song @ 2026-03-20 19:09 UTC (permalink / raw)
To: Alan Maguire, Arnaldo Carvalho de Melo, dwarves
Cc: Alexei Starovoitov, Andrii Nakryiko, bpf, kernel-team
Ensure to skip optimized parameter so btf can generate
proper true signatures.
In the first patch of the patch set, with DW_CC_nocall filtering, 875 functions
have signature changed. With a series of improvement, eventually only 17 functions
remain and unfortunately these functions cannot be converted to true signatures
due to locations. For example,
0x0242f1f7: DW_TAG_subprogram
DW_AT_name ("memblock_find_in_range")
DW_AT_calling_convention (DW_CC_nocall)
DW_AT_type (0x0242decc "phys_addr_t")
...
0x0242f22e: DW_TAG_formal_parameter
DW_AT_location (indexed (0x14a) loclist = 0x005595bc:
[0xffffffff87a000f9, 0xffffffff87a00178): DW_OP_reg5 RDI
[0xffffffff87a00178, 0xffffffff87a001be): DW_OP_reg14 R14
[0xffffffff87a001be, 0xffffffff87a001c7): DW_OP_entry_value(DW_OP_reg5 RDI), DW_OP_stack_value
[0xffffffff87a001c7, 0xffffffff87a00214): DW_OP_reg14 R14)
DW_AT_name ("start")
DW_AT_type (0x0242decc "phys_addr_t")
...
0x0242f239: DW_TAG_formal_parameter
DW_AT_location (indexed (0x14b) loclist = 0x005595e6:
[0xffffffff87a000f9, 0xffffffff87a00175): DW_OP_reg4 RSI
[0xffffffff87a00175, 0xffffffff87a001b8): DW_OP_reg3 RBX
[0xffffffff87a001b8, 0xffffffff87a001c7): DW_OP_entry_value(DW_OP_reg4 RSI), DW_OP_stack_value
[0xffffffff87a001c7, 0xffffffff87a00214): DW_OP_reg3 RBX)
DW_AT_name ("end")
DW_AT_type (0x0242decc "phys_addr_t")
...
0x0242f245: DW_TAG_formal_parameter
DW_AT_location (indexed (0x14c) loclist = 0x00559610:
[0xffffffff87a001e3, 0xffffffff87a001ef): DW_OP_breg4 RSI+0)
DW_AT_name ("size")
DW_AT_type (0x0242decc "phys_addr_t")
...
0x0242f250: DW_TAG_formal_parameter
DW_AT_const_value (4096)
DW_AT_name ("align")
DW_AT_type (0x0242decc "phys_addr_t")
...
The third parameter 'size' is not from RDX. Hence, true signature is not possible for this function.
I also did some experiments on arm64. The number of signature-changed funcitons
is 863 and finally there are 79 functions cannot be converted to true signatures.
Through dwarf comparison of x86_64 vs. arm64, llvm arm64 backend looks like having
more relaxation to compute parameter values for those signature-changed functions.
Signed-off-by: Yonghong Song <yonghong.song@linux.dev>
---
btf_encoder.c | 13 +++++++++++--
1 file changed, 11 insertions(+), 2 deletions(-)
diff --git a/btf_encoder.c b/btf_encoder.c
index d36984a..8e991b1 100644
--- a/btf_encoder.c
+++ b/btf_encoder.c
@@ -1257,15 +1257,21 @@ static int32_t btf_encoder__save_func(struct btf_encoder *encoder, struct functi
struct btf *btf = encoder->btf;
struct llvm_annotation *annot;
struct parameter *param;
- uint8_t param_idx = 0;
+ uint8_t param_idx = 0, skip_idx = 0;
int str_off, err = 0;
if (!state)
return -ENOMEM;
+ if (encoder->cu->producer_clang) {
+ ftype__for_each_parameter(ftype, param) {
+ if (param->optimized) skip_idx++;
+ }
+ }
+
state->addr = function__addr(fn);
state->elf = func;
- state->nr_parms = ftype->nr_parms + (ftype->unspec_parms ? 1 : 0);
+ state->nr_parms = ftype->nr_parms - skip_idx + (ftype->unspec_parms ? 1 : 0);
state->ret_type_id = ftype->tag.type == 0 ? 0 : encoder->type_id_off + ftype->tag.type;
if (state->nr_parms > 0) {
state->parms = zalloc(state->nr_parms * sizeof(*state->parms));
@@ -1303,6 +1309,9 @@ static int32_t btf_encoder__save_func(struct btf_encoder *encoder, struct functi
state->nr_parms--;
continue;
}
+ if (encoder->cu->producer_clang && param->optimized)
+ continue;
+
name = parameter__name(param) ?: "";
str_off = btf__add_str(btf, name);
if (str_off < 0) {
--
2.52.0
^ permalink raw reply related [flat|nested] 20+ messages in thread
* [PATCH dwarves v3 9/9] tests: Add a few clang true signature tests
2026-03-20 19:09 [PATCH dwarves v3 0/9] pahole: Encode true signatures in kernel BTF Yonghong Song
` (7 preceding siblings ...)
2026-03-20 19:09 ` [PATCH dwarves v3 8/9] btf_encoder: Handle optimized parameter properly Yonghong Song
@ 2026-03-20 19:10 ` Yonghong Song
2026-03-23 15:41 ` Alan Maguire
8 siblings, 1 reply; 20+ messages in thread
From: Yonghong Song @ 2026-03-20 19:10 UTC (permalink / raw)
To: Alan Maguire, Arnaldo Carvalho de Melo, dwarves
Cc: Alexei Starovoitov, Andrii Nakryiko, bpf, kernel-team
Three tests are added.
Test 1: VERBOSE=1 ./clang_parm_optimized.sh
BTF: char * foo(struct t * a, struct t * d);
DWARF: char * foo(struct t * a, int b, struct t * d);
where parameber 'b' is unused.
Test 2: VERBOSE=1 ./clang_parm_optimized_stack.sh
BTF: char * foo(struct t * a, struct t * d);
DWARF: char * foo(struct t * a, int b1, int b2, int b3, int b4, int b5, int b6, struct t * d);
where parameters 'b1' to 'b6' are unused.
Test 3: VERBOSE=1 ./clang_parm_aggregate.sh
BTF: long foo(long a__f1, struct t b, int i);
DWARF: long foo(struct t a, struct t b, int i);
where the 'struct t' definition is 'struct t { long f1; long f2; };', and
a.f2 is not used in the function.
Signed-off-by: Yonghong Song <yonghong.song@linux.dev>
---
tests/clang_parm_aggregate.sh | 63 +++++++++++++++++++++++
tests/clang_parm_optimized.sh | 77 +++++++++++++++++++++++++++++
tests/clang_parm_optimized_stack.sh | 77 +++++++++++++++++++++++++++++
3 files changed, 217 insertions(+)
create mode 100755 tests/clang_parm_aggregate.sh
create mode 100755 tests/clang_parm_optimized.sh
create mode 100755 tests/clang_parm_optimized_stack.sh
diff --git a/tests/clang_parm_aggregate.sh b/tests/clang_parm_aggregate.sh
new file mode 100755
index 0000000..bf47c8c
--- /dev/null
+++ b/tests/clang_parm_aggregate.sh
@@ -0,0 +1,63 @@
+#!/bin/bash
+# SPDX-License-Identifier: GPL-2.0-only
+
+source test_lib.sh
+
+outdir=$(make_tmpdir)
+
+# Comment this out to save test data.
+trap cleanup EXIT
+
+title_log "Validation of BTF encoding of true_signatures."
+
+clang_true="${outdir}/clang_true"
+CC=$(which clang 2>/dev/null)
+
+if [[ -z "$CC" ]]; then
+ info_log "skip: clang not available"
+ test_skip
+fi
+
+cat > ${clang_true}.c << EOF
+struct t { long f1; long f2; };
+__attribute__((noinline)) static long foo(struct t a, struct t b, int i)
+{
+ return a.f1 + b.f1 + b.f2 + i;
+}
+
+struct t p1, p2;
+int i;
+int main()
+{
+ return (int)foo(p1, p2, i);
+}
+EOF
+
+CFLAGS="$CFLAGS -g -O2"
+${CC} ${CFLAGS} -o $clang_true ${clang_true}.c
+if [[ $? -ne 0 ]]; then
+ error_log "Could not compile ${clang_true}.c"
+ test_fail
+fi
+LLVM_OBJCOPY=objcopy pahole -J --btf_features=+true_signature $clang_true
+if [[ $? -ne 0 ]]; then
+ error_log "Could not encode BTF for $clang_true"
+ test_fail
+fi
+
+btf_optimized=$(pfunct --all --format_path=btf $clang_true |grep "foo")
+if [[ -z "$btf_optimized" ]]; then
+ info_log "skip: no optimizations applied."
+ test_skip
+fi
+
+btf_cmp=$btf_optimized
+dwarf=$(pfunct --all $clang_true |grep "foo")
+
+verbose_log "BTF: $btf_optimized DWARF: $dwarf"
+
+if [[ "$btf_cmp" == "$dwarf" ]]; then
+ error_log "BTF and DWARF signatures should be different and they are not: BTF: $btf_optimized ; DWARF $dwarf"
+ test_fail
+fi
+test_pass
diff --git a/tests/clang_parm_optimized.sh b/tests/clang_parm_optimized.sh
new file mode 100755
index 0000000..379e6d5
--- /dev/null
+++ b/tests/clang_parm_optimized.sh
@@ -0,0 +1,77 @@
+#!/bin/bash
+# SPDX-License-Identifier: GPL-2.0-only
+
+source test_lib.sh
+
+outdir=$(make_tmpdir)
+
+# Comment this out to save test data.
+trap cleanup EXIT
+
+title_log "Validation of BTF encoding of true_signatures."
+
+clang_true="${outdir}/clang_true"
+CC=$(which clang 2>/dev/null)
+
+if [[ -z "$CC" ]]; then
+ info_log "skip: clang not available"
+ test_skip
+fi
+
+cat > ${clang_true}.c << EOF
+struct t { int a; };
+__attribute__((noinline)) char *tar(struct t *a, struct t *d)
+{
+ if (a->a == d->a)
+ return (char *)10;
+ else
+ return (char *)0;
+}
+
+__attribute__((noinline)) static char * foo(struct t *a, int b, struct t *d)
+{
+ return tar(a, d);
+}
+
+__attribute__((noinline)) char *bar(struct t *a, struct t *d)
+{
+ return foo(a, 1, d);
+}
+
+struct t p1, p2;
+int main()
+{
+ return !!bar(&p1, &p2);
+}
+EOF
+
+CFLAGS="$CFLAGS -g -O2"
+${CC} ${CFLAGS} -o $clang_true ${clang_true}.c
+if [[ $? -ne 0 ]]; then
+ error_log "Could not compile ${clang_true}.c"
+ test_fail
+fi
+LLVM_OBJCOPY=objcopy pahole -J --btf_features=+true_signature $clang_true
+if [[ $? -ne 0 ]]; then
+ error_log "Could not encode BTF for $clang_true"
+ test_fail
+fi
+
+btf_optimized=$(pfunct --all --format_path=btf $clang_true |grep "foo")
+if [[ -z "$btf_optimized" ]]; then
+ info_log "skip: no optimizations applied."
+ test_skip
+fi
+
+btf_cmp=$btf_optimized
+dwarf=$(pfunct --all $clang_true |grep "foo")
+
+if [[ -n "$VERBOSE" ]]; then
+ printf " BTF: %s DWARF: %s\n" "$btf_optimized" "$dwarf"
+fi
+
+if [[ "$btf_cmp" == "$dwarf" ]]; then
+ error_log "BTF and DWARF signatures should be different and they are not: BTF: $btf_optimized ; DWARF $dwarf"
+ test_fail
+fi
+test_pass
diff --git a/tests/clang_parm_optimized_stack.sh b/tests/clang_parm_optimized_stack.sh
new file mode 100755
index 0000000..8638af7
--- /dev/null
+++ b/tests/clang_parm_optimized_stack.sh
@@ -0,0 +1,77 @@
+#!/bin/bash
+# SPDX-License-Identifier: GPL-2.0-only
+
+source test_lib.sh
+
+outdir=$(make_tmpdir)
+
+# Comment this out to save test data.
+trap cleanup EXIT
+
+title_log "Validation of BTF encoding of true_signatures."
+
+clang_true="${outdir}/clang_true"
+CC=$(which clang 2>/dev/null)
+
+if [[ -z "$CC" ]]; then
+ info_log "skip: clang not available"
+ test_skip
+fi
+
+cat > ${clang_true}.c << EOF
+struct t { int a; };
+__attribute__((noinline)) char *tar(struct t *a, struct t *d)
+{
+ if (a->a == d->a)
+ return (char *)10;
+ else
+ return (char *)0;
+}
+
+__attribute__((noinline)) static char * foo(struct t *a, int b1, int b2, int b3, int b4, int b5, int b6, struct t *d)
+{
+ return tar(a, d);
+}
+
+__attribute__((noinline)) char *bar(struct t *a, struct t *d)
+{
+ return foo(a, 1, 2, 3, 4, 5, 6, d);
+}
+
+struct t p1, p2;
+int main()
+{
+ return !!bar(&p1, &p2);
+}
+EOF
+
+CFLAGS="$CFLAGS -g -O2"
+${CC} ${CFLAGS} -o $clang_true ${clang_true}.c
+if [[ $? -ne 0 ]]; then
+ error_log "Could not compile ${clang_true}.c"
+ test_fail
+fi
+LLVM_OBJCOPY=objcopy pahole -J --btf_features=+true_signature $clang_true
+if [[ $? -ne 0 ]]; then
+ error_log "Could not encode BTF for $clang_true"
+ test_fail
+fi
+
+btf_optimized=$(pfunct --all --format_path=btf $clang_true |grep "foo")
+if [[ -z "$btf_optimized" ]]; then
+ info_log "skip: no optimizations applied."
+ test_skip
+fi
+
+btf_cmp=$btf_optimized
+dwarf=$(pfunct --all $clang_true |grep "foo")
+
+if [[ -n "$VERBOSE" ]]; then
+ printf " BTF: %s DWARF: %s\n" "$btf_optimized" "$dwarf"
+fi
+
+if [[ "$btf_cmp" == "$dwarf" ]]; then
+ error_log "BTF and DWARF signatures should be different and they are not: BTF: $btf_optimized ; DWARF $dwarf"
+ test_fail
+fi
+test_pass
--
2.52.0
^ permalink raw reply related [flat|nested] 20+ messages in thread
* Re: [PATCH dwarves v3 7/9] dwarf_loader: Handle expression lists
2026-03-20 19:09 ` [PATCH dwarves v3 7/9] dwarf_loader: Handle expression lists Yonghong Song
@ 2026-03-21 23:10 ` Jiri Olsa
2026-03-22 18:33 ` Yonghong Song
0 siblings, 1 reply; 20+ messages in thread
From: Jiri Olsa @ 2026-03-21 23:10 UTC (permalink / raw)
To: Yonghong Song
Cc: Alan Maguire, Arnaldo Carvalho de Melo, dwarves,
Alexei Starovoitov, Andrii Nakryiko, bpf, kernel-team
On Fri, Mar 20, 2026 at 12:09:53PM -0700, Yonghong Song wrote:
SNIP
> + if (byte_size <= cu->addr_size || !cu->agg_use_two_regs) {
> + switch (expr[0].atom) {
> + case DW_OP_reg0 ... DW_OP_reg31:
> + if (loc_num != 0)
> + break;
> + *ret = expr[0].atom;
> + if (*ret == expected_reg)
> + return *ret;
> + break;
> + case DW_OP_breg0 ... DW_OP_breg31:
> + if (loc_num != 0)
> + break;
> + bool has_op_stack_value = false;
> + for (int i = 1; i < exprlen; i++) {
> + if (expr[i].atom == DW_OP_stack_value) {
> + has_op_stack_value = true;
> + break;
> + }
> + }
> + if (!has_op_stack_value)
> + break;
> + /* The existence of DW_OP_stack_value means that
> + * DW_OP_bregX register is used as value.
> + */
> + *ret = expr[0].atom - DW_OP_breg0 + DW_OP_reg0;
> + if (*ret == expected_reg)
> + return *ret;
> + }
> + } else {
> + /* cu->addr * 2 */
> + int off = 0;
> + for (int i = 0; i < exprlen; i++) {
> + if (expr[i].atom == DW_OP_piece) {
> + int num = expr[i].number;
> + if (i == 0) {
> + off = num;
> + continue;
> + }
> + if (off < cu->addr_size) (*lower_half) |= (1 << off);
> + else (*upper_half) |= (1 << (off - cu->addr_size));
> + off += num;
this is really hard for me to read.. I think it needs to follow common
formatting rules and it deserves some explanation either in comments
or in changelog
> + } else if (expr[i].atom >= DW_OP_reg0 && expr[i].atom <= DW_OP_reg31) {
> + if (off < cu->addr_size)
> + *ret = expr[i].atom;
> + else if (*ret < 0)
> + *ret = expr[i].atom;
> + }
> + /* FIXME: not handling DW_OP_bregX yet since we do not have
> + * a use case for it yet for linux kernel.
> + */
> + }
> + }
> +
> return PARM_CONTINUE;
> }
>
> +/* The lower_half and upper_half, computed in parameter__multi_exprs(), are handled here.
> + */
> +static int parameter__handle_two_addr_len(int expected_reg, unsigned long lower_half, unsigned long upper_half,
> + int ret, Dwarf_Die *die, struct conf_load *conf, struct cu *cu,
> + struct parameter *parm) {
> + if (!lower_half && !upper_half)
> + return ret;
> +
> + if (ret != expected_reg)
> + return ret;
> +
> + if (!conf->true_signature)
> + return PARM_DEFAULT_FAIL;
> +
> + /* Both halfs are used based on dwarf */
> + if (lower_half && upper_half)
> + return PARM_TWO_ADDR_LEN;
> +
> + /* FIXME: parm->name may be NULL due to abstract origin. We do not want to
> + * update abstract origin as the type in abstract origin may be used
> + * in some other places. We could remove abstract origin in this parameter
> + * and add name and type in parameter itself. Right now, for current bpf-next
> + * repo, we do not have instances below where parm->name is NULL for x86_64 arch.
> + */
> + if (!parm->name)
> + return PARM_TO_BE_IMPROVED;
> +
> + /* FIXME: Only support single field now so we can have a good parameter name and
> + * type for it.
> + */
> + if (__builtin_popcountll(lower_half) >= 2 || __builtin_popcountll(upper_half) >= 2)
> + return PARM_TO_BE_IMPROVED;
> +
> + int field_offset;
> + if (__builtin_popcountll(lower_half) == 1)
> + field_offset = __builtin_ctzll(lower_half);
> + else
> + field_offset = cu->addr_size + __builtin_ctzll(upper_half);
> +
> + /* FIXME: Only struct type is supported. */
> + Dwarf_Die member_die;
> + if (!get_member_with_offset(die, field_offset, &member_die))
> + return PARM_TO_BE_IMPROVED;
> +
> + const char *member_name = attr_string(&member_die, DW_AT_name, conf);
> + int len = sizeof(parm->name) + strlen(member_name) + 3;
this seems wrong, shoud be strlen for parm->name? maybe asprintf is
better option in here?
> + char *new_name = malloc(len);
also there's cu__malloc, and we should check if the allocation failed
> + sprintf(new_name, "%s__%s", parm->name, member_name);
> + parm->name = new_name;
I wonder this will leak, because normally the name is allocated with
dwarf_formstring and we don't need to free it, but now we do
jirka
^ permalink raw reply [flat|nested] 20+ messages in thread
* Re: [PATCH dwarves v3 1/9] dwarf_loader: Reduce parameter checking with clang DW_AT_calling_convention attr
2026-03-20 19:09 ` [PATCH dwarves v3 1/9] dwarf_loader: Reduce parameter checking with clang DW_AT_calling_convention attr Yonghong Song
@ 2026-03-21 23:10 ` Jiri Olsa
2026-03-22 17:36 ` Yonghong Song
0 siblings, 1 reply; 20+ messages in thread
From: Jiri Olsa @ 2026-03-21 23:10 UTC (permalink / raw)
To: Yonghong Song
Cc: Alan Maguire, Arnaldo Carvalho de Melo, dwarves,
Alexei Starovoitov, Andrii Nakryiko, bpf, kernel-team
On Fri, Mar 20, 2026 at 12:09:22PM -0700, Yonghong Song wrote:
> Currently every function is checked for its parameters to identify whether
> the signature changed or not. If signature indeed changed, pahole may do
> some adjustment for parameters for true signatures.
>
> In clang, any function with the following attribute
> DW_AT_calling_convention (DW_CC_nocall)
> indicates this function having signature changed.
> pahole can take advantage of this to avoid parameter checking if
> DW_AT_calling_convention is not DW_CC_nocall.
>
> But more importantly, DW_CC_nocall can identify signature-changed functions
> and parameters can be checked one-after-another to create the true
> signatures. Otherwise, it takes more effort to identify whether a
> function has signature changed or not. For example, for funciton
> __bpf_kfunc static void bbr_main(struct sock *sk, u32 ack, int flag,
> const struct rate_sample *rs) { ... }
> and bbr_main() is a callback function in
> .cong_control = bbr_main
> in 'struct tcp_congestion_ops tcp_bbr_cong_ops'.
> In the above bbr_main(...), parameter 'ack' and 'flag' are not used.
> The following are some details:
>
> 0x0a713b8d: DW_TAG_formal_parameter
> DW_AT_location (indexed (0x28) loclist = 0x0166d452:
> [0xffffffff83e77fd9, 0xffffffff83e78016): DW_OP_reg5 RDI
> ...
> DW_AT_name ("sk")
> DW_AT_type (0x0a6f5b2b "sock *")
> ...
>
> 0x0a713b98: DW_TAG_formal_parameter
> DW_AT_name ("ack")
> DW_AT_type (0x0a6f58fd "u32")
> ...
>
> 0x0a713ba2: DW_TAG_formal_parameter
> DW_AT_name ("flag")
> DW_AT_type (0x0a6f57d1 "int")
> ...
>
> 0x0a713bac: DW_TAG_formal_parameter
> DW_AT_location (indexed (0x29) loclist = 0x0166d4a8:
> [0xffffffff83e77fd9, 0xffffffff83e78016): DW_OP_reg2 RCX
> ...
> DW_AT_name ("rs")
> DW_AT_type (0x0a710da5 "const rate_sample *")
> DW_AT_decl_line (1027)
>
> Some analysis for the above dwarf can conclude that the 'ark' and 'flag'
> may be related to RSI and RDX, considering the last one is RCX. Basically this
> requires all parameters are available to collectively decide whether the
> true signature can be found or not. In such case, DW_CC_nocall can make things
> easier as parameter can be checked one after another.
>
> For a clang built bpf-next kernel, in non-LTO setup, the number of kernel functions
> is 69103 and the number of signature changed functions is 875, based on
> DW_AT_calling_convention (DW_CC_nocall)
> indication.
we don't display these stats, right? would be great and probably easy
to count different flags and aggregate them
>
> Among 875 signature changed functions, after this patch, 495 functions
> can have proper true signatures, mostly due to simple dead argument
> elimination. The number of remaining functions, which cannot get the
> true signature, is 379. They will be addressed in the subsequent commits.
after this change I have more functions added (below) and I checked
few and they seem ok (w/o DW_CC_nocall)
jirka
acpi_ex_do_debug_object
add_bits
amd_pstate_get_mode_string
dma_alloc_from_contiguous
do_set_pmd
dst_destroy
find_cpio_data
find_microcode_in_initrd
ima_write_policy
insn_init
io_tx_ubuf_complete
ip6_protocol_deliver_rcu
kvm_tdp_mmu_unmap_gfn_range
net_dim_get_def_rx_moderation
net_dim_get_def_tx_moderation
pinctrl_commit_state
string_unescape
syscall_copy_user_array
tdp_mmu_zap_leafs
usb_speed_string
__vlan_find_dev_deep_rcu
__vxlan_fdb_delete
xfs_bmbt_maxrecs
xfs_inobt_maxrecs
ZSTD_buildSequencesStatistics
ZSTD_copyCCtx
ZSTD_findFrameSizeInfo
ZSTD_get1BlockSummary
zstd_get_cparams
ZSTD_getCParams
ZSTD_getCParamsFromCCtxParams
ZSTD_getCParamsFromCDict
ZSTD_getCParams_internal
zstd_get_params
ZSTD_getParams
^ permalink raw reply [flat|nested] 20+ messages in thread
* Re: [PATCH dwarves v3 2/9] dwarf_loader: Handle signatures with dead arguments
2026-03-20 19:09 ` [PATCH dwarves v3 2/9] dwarf_loader: Handle signatures with dead arguments Yonghong Song
@ 2026-03-21 23:10 ` Jiri Olsa
2026-03-22 18:03 ` Yonghong Song
0 siblings, 1 reply; 20+ messages in thread
From: Jiri Olsa @ 2026-03-21 23:10 UTC (permalink / raw)
To: Yonghong Song
Cc: Alan Maguire, Arnaldo Carvalho de Melo, dwarves,
Alexei Starovoitov, Andrii Nakryiko, bpf, kernel-team
On Fri, Mar 20, 2026 at 12:09:27PM -0700, Yonghong Song wrote:
> For llvm dwarf, the dead argument may be in the middle of
> DW_TAG_subprogram. So we introduce skip_idx in order to
> match expected registers properly.
>
> For example:
> 0x00042897: DW_TAG_subprogram
> DW_AT_name ("create_dev")
> DW_AT_calling_convention (DW_CC_nocall)
> DW_AT_type (0x0002429a "int")
> ...
>
> 0x000428ab: DW_TAG_formal_parameter
> DW_AT_name ("name")
> DW_AT_type (0x000242ed "char *")
> ...
>
> 0x000428b5: DW_TAG_formal_parameter
> DW_AT_location (indexed (0x3f) loclist = 0x000027f8:
> [0xffffffff87681370, 0xffffffff8768137a): DW_OP_reg5 RDI
> [0xffffffff8768137a, 0xffffffff87681392): DW_OP_reg3 RBX
> [0xffffffff87681392, 0xffffffff876813ae): DW_OP_entry_value(DW_OP_reg5 RDI), DW_OP_stack_value)
> DW_AT_name ("dev")
> DW_AT_type (0x00026859 "dev_t")
> ...
>
> With skip_idx, we can identify that the second original argument
> 'dev' becomes the first one after optimization.
hi,
this change removes for me functions below and some of them (ata_dev_select,
dmi_save_type, perhaps more) seem to be removed because their last 2 arguments
are constants IIUC, which does not seem to be what the changelog suggests,
but I guess it's still correct (it's without +true_signature)
jirka
ata_dev_select
__cgroup1_procs_write
check_buffer_access
dax_disassociate_entry
devlink_nl_sb_port_pool_fill
dmi_format_ids
dmi_save_type
dmi_save_uuid
get_buffer
get_net_track
gue_remcsum
icmpv4_xrlim_allow
insert_vmap_area_augment
__intel_pmu_enable_all
ip6addrlbl_fill
ip6_dst_store
kernelmode_fixup_or_oops
merge_note_headers_elf32
merge_note_headers_elf64
mt_destroy_walk
__mutex_lock
__netdev_walk_all_lower_dev
pci_create_device_link
populate_kprobe_blacklist
proc_get_long
rt_mutex_adjust_prio_chain
rt_set_nexthop
run_lwt_bpf
simple_attr_write_xsigned
__skb_gro_checksum_validate_needed
tclass_notify
tg_set_conf
toggle_bp_slot
trace_event_get_offsets_aer_event
trace_event_get_offsets_br_fdb_external_learn_add
trace_event_get_offsets_br_fdb_update
trace_event_get_offsets_cache_tag_flush
trace_event_get_offsets_devlink_health_recover_aborted
trace_event_get_offsets_iommu_error
trace_event_get_offsets_prq_report
virtio_net_hdr_from_skb
writeback_inodes_wb
xfs_file_dio_write_aligned
>
> Signed-off-by: Yonghong Song <yonghong.song@linux.dev>
> ---
> dwarf_loader.c | 19 +++++++++++++++++--
> 1 file changed, 17 insertions(+), 2 deletions(-)
>
> diff --git a/dwarf_loader.c b/dwarf_loader.c
> index 21f8bf1..a6e6587 100644
> --- a/dwarf_loader.c
> +++ b/dwarf_loader.c
> @@ -1192,6 +1192,7 @@ static ptrdiff_t __dwarf_getlocations(Dwarf_Attribute *attr,
>
> struct func_info {
> bool signature_changed;
> + int skip_idx;
> };
>
> /* For DW_AT_location 'attr':
> @@ -1264,6 +1265,7 @@ static struct parameter *parameter__new(Dwarf_Die *die, struct cu *cu,
> if (parm != NULL) {
> bool has_const_value;
> Dwarf_Attribute attr;
> + int reg_idx;
>
> tag__init(&parm->tag, cu, die);
> parm->name = attr_string(die, DW_AT_name, conf);
> @@ -1273,7 +1275,18 @@ static struct parameter *parameter__new(Dwarf_Die *die, struct cu *cu,
> if (!info->signature_changed) {
> if (cu->producer_clang || param_idx >= cu->nr_register_params)
> return parm;
> + } else {
> + /* if true_signature is not enabled, mark parameter as
> + * unexpected_reg since there is a skipped parameter before.
> + */
> + if (!conf->true_signature && info->skip_idx) {
> + parm->unexpected_reg = 1;
> + return parm;
> + }
> }
> + reg_idx = param_idx - info->skip_idx;
> + if (reg_idx >= cu->nr_register_params)
> + return parm;
> /* Parameters which use DW_AT_abstract_origin to point at
> * the original parameter definition (with no name in the DIE)
> * are the result of later DWARF generation during compilation
> @@ -1311,7 +1324,7 @@ static struct parameter *parameter__new(Dwarf_Die *die, struct cu *cu,
> parm->has_loc = dwarf_attr(die, DW_AT_location, &attr) != NULL;
>
> if (parm->has_loc) {
> - int expected_reg = cu->register_params[param_idx];
> + int expected_reg = cu->register_params[reg_idx];
> int actual_reg = parameter__reg(&attr, expected_reg);
>
> if (actual_reg < 0)
> @@ -1324,8 +1337,10 @@ static struct parameter *parameter__new(Dwarf_Die *die, struct cu *cu,
> * contents.
> */
> parm->unexpected_reg = 1;
> - } else if (has_const_value) {
> + } else if (has_const_value || info->signature_changed) {
> parm->optimized = 1;
> + if (info->signature_changed)
> + info->skip_idx++;
> }
> }
>
> --
> 2.52.0
>
>
^ permalink raw reply [flat|nested] 20+ messages in thread
* Re: [PATCH dwarves v3 1/9] dwarf_loader: Reduce parameter checking with clang DW_AT_calling_convention attr
2026-03-21 23:10 ` Jiri Olsa
@ 2026-03-22 17:36 ` Yonghong Song
2026-03-23 12:56 ` Alan Maguire
0 siblings, 1 reply; 20+ messages in thread
From: Yonghong Song @ 2026-03-22 17:36 UTC (permalink / raw)
To: Jiri Olsa
Cc: Alan Maguire, Arnaldo Carvalho de Melo, dwarves,
Alexei Starovoitov, Andrii Nakryiko, bpf, kernel-team
On 3/21/26 4:10 PM, Jiri Olsa wrote:
> On Fri, Mar 20, 2026 at 12:09:22PM -0700, Yonghong Song wrote:
>> Currently every function is checked for its parameters to identify whether
>> the signature changed or not. If signature indeed changed, pahole may do
>> some adjustment for parameters for true signatures.
>>
>> In clang, any function with the following attribute
>> DW_AT_calling_convention (DW_CC_nocall)
>> indicates this function having signature changed.
>> pahole can take advantage of this to avoid parameter checking if
>> DW_AT_calling_convention is not DW_CC_nocall.
>>
>> But more importantly, DW_CC_nocall can identify signature-changed functions
>> and parameters can be checked one-after-another to create the true
>> signatures. Otherwise, it takes more effort to identify whether a
>> function has signature changed or not. For example, for funciton
>> __bpf_kfunc static void bbr_main(struct sock *sk, u32 ack, int flag,
>> const struct rate_sample *rs) { ... }
>> and bbr_main() is a callback function in
>> .cong_control = bbr_main
>> in 'struct tcp_congestion_ops tcp_bbr_cong_ops'.
>> In the above bbr_main(...), parameter 'ack' and 'flag' are not used.
>> The following are some details:
>>
>> 0x0a713b8d: DW_TAG_formal_parameter
>> DW_AT_location (indexed (0x28) loclist = 0x0166d452:
>> [0xffffffff83e77fd9, 0xffffffff83e78016): DW_OP_reg5 RDI
>> ...
>> DW_AT_name ("sk")
>> DW_AT_type (0x0a6f5b2b "sock *")
>> ...
>>
>> 0x0a713b98: DW_TAG_formal_parameter
>> DW_AT_name ("ack")
>> DW_AT_type (0x0a6f58fd "u32")
>> ...
>>
>> 0x0a713ba2: DW_TAG_formal_parameter
>> DW_AT_name ("flag")
>> DW_AT_type (0x0a6f57d1 "int")
>> ...
>>
>> 0x0a713bac: DW_TAG_formal_parameter
>> DW_AT_location (indexed (0x29) loclist = 0x0166d4a8:
>> [0xffffffff83e77fd9, 0xffffffff83e78016): DW_OP_reg2 RCX
>> ...
>> DW_AT_name ("rs")
>> DW_AT_type (0x0a710da5 "const rate_sample *")
>> DW_AT_decl_line (1027)
>>
>> Some analysis for the above dwarf can conclude that the 'ark' and 'flag'
>> may be related to RSI and RDX, considering the last one is RCX. Basically this
>> requires all parameters are available to collectively decide whether the
>> true signature can be found or not. In such case, DW_CC_nocall can make things
>> easier as parameter can be checked one after another.
>>
>> For a clang built bpf-next kernel, in non-LTO setup, the number of kernel functions
>> is 69103 and the number of signature changed functions is 875, based on
>> DW_AT_calling_convention (DW_CC_nocall)
>> indication.
> we don't display these stats, right? would be great and probably easy
> to count different flags and aggregate them
The actual stats will be different depending on kernel code and compiler optimization.
But I think I can still count them for each commit so people will know
which change caused how much true signature.
>
>> Among 875 signature changed functions, after this patch, 495 functions
>> can have proper true signatures, mostly due to simple dead argument
>> elimination. The number of remaining functions, which cannot get the
>> true signature, is 379. They will be addressed in the subsequent commits.
> after this change I have more functions added (below) and I checked
> few and they seem ok (w/o DW_CC_nocall)
Most global functions should be okay. But some global functions
esp. if argument is more than 8 byte (struct type), they may be
considered as signature change with the current implementation.
>
> jirka
>
>
> acpi_ex_do_debug_object
> add_bits
> amd_pstate_get_mode_string
> dma_alloc_from_contiguous
> do_set_pmd
> dst_destroy
> find_cpio_data
> find_microcode_in_initrd
> ima_write_policy
> insn_init
> io_tx_ubuf_complete
> ip6_protocol_deliver_rcu
> kvm_tdp_mmu_unmap_gfn_range
> net_dim_get_def_rx_moderation
> net_dim_get_def_tx_moderation
> pinctrl_commit_state
> string_unescape
> syscall_copy_user_array
> tdp_mmu_zap_leafs
> usb_speed_string
> __vlan_find_dev_deep_rcu
> __vxlan_fdb_delete
> xfs_bmbt_maxrecs
> xfs_inobt_maxrecs
> ZSTD_buildSequencesStatistics
> ZSTD_copyCCtx
> ZSTD_findFrameSizeInfo
> ZSTD_get1BlockSummary
> zstd_get_cparams
> ZSTD_getCParams
> ZSTD_getCParamsFromCCtxParams
> ZSTD_getCParamsFromCDict
> ZSTD_getCParams_internal
> zstd_get_params
> ZSTD_getParams
^ permalink raw reply [flat|nested] 20+ messages in thread
* Re: [PATCH dwarves v3 2/9] dwarf_loader: Handle signatures with dead arguments
2026-03-21 23:10 ` Jiri Olsa
@ 2026-03-22 18:03 ` Yonghong Song
0 siblings, 0 replies; 20+ messages in thread
From: Yonghong Song @ 2026-03-22 18:03 UTC (permalink / raw)
To: Jiri Olsa
Cc: Alan Maguire, Arnaldo Carvalho de Melo, dwarves,
Alexei Starovoitov, Andrii Nakryiko, bpf, kernel-team
On 3/21/26 4:10 PM, Jiri Olsa wrote:
> On Fri, Mar 20, 2026 at 12:09:27PM -0700, Yonghong Song wrote:
>> For llvm dwarf, the dead argument may be in the middle of
>> DW_TAG_subprogram. So we introduce skip_idx in order to
>> match expected registers properly.
>>
>> For example:
>> 0x00042897: DW_TAG_subprogram
>> DW_AT_name ("create_dev")
>> DW_AT_calling_convention (DW_CC_nocall)
>> DW_AT_type (0x0002429a "int")
>> ...
>>
>> 0x000428ab: DW_TAG_formal_parameter
>> DW_AT_name ("name")
>> DW_AT_type (0x000242ed "char *")
>> ...
>>
>> 0x000428b5: DW_TAG_formal_parameter
>> DW_AT_location (indexed (0x3f) loclist = 0x000027f8:
>> [0xffffffff87681370, 0xffffffff8768137a): DW_OP_reg5 RDI
>> [0xffffffff8768137a, 0xffffffff87681392): DW_OP_reg3 RBX
>> [0xffffffff87681392, 0xffffffff876813ae): DW_OP_entry_value(DW_OP_reg5 RDI), DW_OP_stack_value)
>> DW_AT_name ("dev")
>> DW_AT_type (0x00026859 "dev_t")
>> ...
>>
>> With skip_idx, we can identify that the second original argument
>> 'dev' becomes the first one after optimization.
> hi,
> this change removes for me functions below and some of them (ata_dev_select,
> dmi_save_type, perhaps more) seem to be removed because their last 2 arguments
> are constants IIUC, which does not seem to be what the changelog suggests,
> but I guess it's still correct (it's without +true_signature)
For this patch, without +true_signature, it can only get true signatures
when the dead arguments at the end of argument list. With +true_signature,
it allows dead arguments before non-dead arguments.
>
> jirka
>
>
> ata_dev_select
> __cgroup1_procs_write
> check_buffer_access
> dax_disassociate_entry
> devlink_nl_sb_port_pool_fill
> dmi_format_ids
> dmi_save_type
> dmi_save_uuid
> get_buffer
> get_net_track
> gue_remcsum
> icmpv4_xrlim_allow
> insert_vmap_area_augment
> __intel_pmu_enable_all
> ip6addrlbl_fill
> ip6_dst_store
> kernelmode_fixup_or_oops
> merge_note_headers_elf32
> merge_note_headers_elf64
> mt_destroy_walk
> __mutex_lock
> __netdev_walk_all_lower_dev
> pci_create_device_link
> populate_kprobe_blacklist
> proc_get_long
> rt_mutex_adjust_prio_chain
> rt_set_nexthop
> run_lwt_bpf
> simple_attr_write_xsigned
> __skb_gro_checksum_validate_needed
> tclass_notify
> tg_set_conf
> toggle_bp_slot
> trace_event_get_offsets_aer_event
> trace_event_get_offsets_br_fdb_external_learn_add
> trace_event_get_offsets_br_fdb_update
> trace_event_get_offsets_cache_tag_flush
> trace_event_get_offsets_devlink_health_recover_aborted
> trace_event_get_offsets_iommu_error
> trace_event_get_offsets_prq_report
> virtio_net_hdr_from_skb
> writeback_inodes_wb
> xfs_file_dio_write_aligned
>
>
>> Signed-off-by: Yonghong Song <yonghong.song@linux.dev>
>> ---
>> dwarf_loader.c | 19 +++++++++++++++++--
>> 1 file changed, 17 insertions(+), 2 deletions(-)
>>
>> diff --git a/dwarf_loader.c b/dwarf_loader.c
>> index 21f8bf1..a6e6587 100644
>> --- a/dwarf_loader.c
>> +++ b/dwarf_loader.c
>> @@ -1192,6 +1192,7 @@ static ptrdiff_t __dwarf_getlocations(Dwarf_Attribute *attr,
>>
>> struct func_info {
>> bool signature_changed;
>> + int skip_idx;
>> };
>>
>> /* For DW_AT_location 'attr':
>> @@ -1264,6 +1265,7 @@ static struct parameter *parameter__new(Dwarf_Die *die, struct cu *cu,
>> if (parm != NULL) {
>> bool has_const_value;
>> Dwarf_Attribute attr;
>> + int reg_idx;
>>
>> tag__init(&parm->tag, cu, die);
>> parm->name = attr_string(die, DW_AT_name, conf);
>> @@ -1273,7 +1275,18 @@ static struct parameter *parameter__new(Dwarf_Die *die, struct cu *cu,
>> if (!info->signature_changed) {
>> if (cu->producer_clang || param_idx >= cu->nr_register_params)
>> return parm;
>> + } else {
>> + /* if true_signature is not enabled, mark parameter as
>> + * unexpected_reg since there is a skipped parameter before.
>> + */
>> + if (!conf->true_signature && info->skip_idx) {
>> + parm->unexpected_reg = 1;
>> + return parm;
>> + }
>> }
>> + reg_idx = param_idx - info->skip_idx;
>> + if (reg_idx >= cu->nr_register_params)
>> + return parm;
>> /* Parameters which use DW_AT_abstract_origin to point at
>> * the original parameter definition (with no name in the DIE)
>> * are the result of later DWARF generation during compilation
>> @@ -1311,7 +1324,7 @@ static struct parameter *parameter__new(Dwarf_Die *die, struct cu *cu,
>> parm->has_loc = dwarf_attr(die, DW_AT_location, &attr) != NULL;
>>
>> if (parm->has_loc) {
>> - int expected_reg = cu->register_params[param_idx];
>> + int expected_reg = cu->register_params[reg_idx];
>> int actual_reg = parameter__reg(&attr, expected_reg);
>>
>> if (actual_reg < 0)
>> @@ -1324,8 +1337,10 @@ static struct parameter *parameter__new(Dwarf_Die *die, struct cu *cu,
>> * contents.
>> */
>> parm->unexpected_reg = 1;
>> - } else if (has_const_value) {
>> + } else if (has_const_value || info->signature_changed) {
>> parm->optimized = 1;
>> + if (info->signature_changed)
>> + info->skip_idx++;
>> }
>> }
>>
>> --
>> 2.52.0
>>
>>
^ permalink raw reply [flat|nested] 20+ messages in thread
* Re: [PATCH dwarves v3 7/9] dwarf_loader: Handle expression lists
2026-03-21 23:10 ` Jiri Olsa
@ 2026-03-22 18:33 ` Yonghong Song
0 siblings, 0 replies; 20+ messages in thread
From: Yonghong Song @ 2026-03-22 18:33 UTC (permalink / raw)
To: Jiri Olsa
Cc: Alan Maguire, Arnaldo Carvalho de Melo, dwarves,
Alexei Starovoitov, Andrii Nakryiko, bpf, kernel-team
On 3/21/26 4:10 PM, Jiri Olsa wrote:
> On Fri, Mar 20, 2026 at 12:09:53PM -0700, Yonghong Song wrote:
>
> SNIP
>
>> + if (byte_size <= cu->addr_size || !cu->agg_use_two_regs) {
>> + switch (expr[0].atom) {
>> + case DW_OP_reg0 ... DW_OP_reg31:
>> + if (loc_num != 0)
>> + break;
>> + *ret = expr[0].atom;
>> + if (*ret == expected_reg)
>> + return *ret;
>> + break;
>> + case DW_OP_breg0 ... DW_OP_breg31:
>> + if (loc_num != 0)
>> + break;
>> + bool has_op_stack_value = false;
>> + for (int i = 1; i < exprlen; i++) {
>> + if (expr[i].atom == DW_OP_stack_value) {
>> + has_op_stack_value = true;
>> + break;
>> + }
>> + }
>> + if (!has_op_stack_value)
>> + break;
>> + /* The existence of DW_OP_stack_value means that
>> + * DW_OP_bregX register is used as value.
>> + */
>> + *ret = expr[0].atom - DW_OP_breg0 + DW_OP_reg0;
>> + if (*ret == expected_reg)
>> + return *ret;
>> + }
>> + } else {
>> + /* cu->addr * 2 */
>> + int off = 0;
>> + for (int i = 0; i < exprlen; i++) {
>> + if (expr[i].atom == DW_OP_piece) {
>> + int num = expr[i].number;
>> + if (i == 0) {
>> + off = num;
>> + continue;
>> + }
>> + if (off < cu->addr_size) (*lower_half) |= (1 << off);
>> + else (*upper_half) |= (1 << (off - cu->addr_size));
>> + off += num;
> this is really hard for me to read.. I think it needs to follow common
> formatting rules and it deserves some explanation either in comments
> or in changelog
Okay, I will add comments to explain what it is.
>
>> + } else if (expr[i].atom >= DW_OP_reg0 && expr[i].atom <= DW_OP_reg31) {
>> + if (off < cu->addr_size)
>> + *ret = expr[i].atom;
>> + else if (*ret < 0)
>> + *ret = expr[i].atom;
>> + }
>> + /* FIXME: not handling DW_OP_bregX yet since we do not have
>> + * a use case for it yet for linux kernel.
>> + */
>> + }
>> + }
>> +
>> return PARM_CONTINUE;
>> }
>>
>> +/* The lower_half and upper_half, computed in parameter__multi_exprs(), are handled here.
>> + */
>> +static int parameter__handle_two_addr_len(int expected_reg, unsigned long lower_half, unsigned long upper_half,
>> + int ret, Dwarf_Die *die, struct conf_load *conf, struct cu *cu,
>> + struct parameter *parm) {
>> + if (!lower_half && !upper_half)
>> + return ret;
>> +
>> + if (ret != expected_reg)
>> + return ret;
>> +
>> + if (!conf->true_signature)
>> + return PARM_DEFAULT_FAIL;
>> +
>> + /* Both halfs are used based on dwarf */
>> + if (lower_half && upper_half)
>> + return PARM_TWO_ADDR_LEN;
>> +
>> + /* FIXME: parm->name may be NULL due to abstract origin. We do not want to
>> + * update abstract origin as the type in abstract origin may be used
>> + * in some other places. We could remove abstract origin in this parameter
>> + * and add name and type in parameter itself. Right now, for current bpf-next
>> + * repo, we do not have instances below where parm->name is NULL for x86_64 arch.
>> + */
>> + if (!parm->name)
>> + return PARM_TO_BE_IMPROVED;
>> +
>> + /* FIXME: Only support single field now so we can have a good parameter name and
>> + * type for it.
>> + */
>> + if (__builtin_popcountll(lower_half) >= 2 || __builtin_popcountll(upper_half) >= 2)
>> + return PARM_TO_BE_IMPROVED;
>> +
>> + int field_offset;
>> + if (__builtin_popcountll(lower_half) == 1)
>> + field_offset = __builtin_ctzll(lower_half);
>> + else
>> + field_offset = cu->addr_size + __builtin_ctzll(upper_half);
>> +
>> + /* FIXME: Only struct type is supported. */
>> + Dwarf_Die member_die;
>> + if (!get_member_with_offset(die, field_offset, &member_die))
>> + return PARM_TO_BE_IMPROVED;
>> +
>> + const char *member_name = attr_string(&member_die, DW_AT_name, conf);
>> + int len = sizeof(parm->name) + strlen(member_name) + 3;
> this seems wrong, shoud be strlen for parm->name? maybe asprintf is
> better option in here?
Thanks for spotting this. It should be strlen. asprintf is even better.
>
>> + char *new_name = malloc(len);
> also there's cu__malloc, and we should check if the allocation failed
Ack
>
>> + sprintf(new_name, "%s__%s", parm->name, member_name);
>> + parm->name = new_name;
> I wonder this will leak, because normally the name is allocated with
> dwarf_formstring and we don't need to free it, but now we do
This will leak. I thought the number of functions for this pattern
is limited. But nevertheless, leaking is not good.
I will wait a little bit for more reviews before sending version 4.
Thanks for review!
>
> jirka
^ permalink raw reply [flat|nested] 20+ messages in thread
* Re: [PATCH dwarves v3 1/9] dwarf_loader: Reduce parameter checking with clang DW_AT_calling_convention attr
2026-03-22 17:36 ` Yonghong Song
@ 2026-03-23 12:56 ` Alan Maguire
2026-03-23 18:32 ` Yonghong Song
0 siblings, 1 reply; 20+ messages in thread
From: Alan Maguire @ 2026-03-23 12:56 UTC (permalink / raw)
To: Yonghong Song, Jiri Olsa
Cc: Arnaldo Carvalho de Melo, dwarves, Alexei Starovoitov,
Andrii Nakryiko, bpf, kernel-team
On 22/03/2026 17:36, Yonghong Song wrote:
>
>
> On 3/21/26 4:10 PM, Jiri Olsa wrote:
>> On Fri, Mar 20, 2026 at 12:09:22PM -0700, Yonghong Song wrote:
>>> Currently every function is checked for its parameters to identify whether
>>> the signature changed or not. If signature indeed changed, pahole may do
>>> some adjustment for parameters for true signatures.
>>>
>>> In clang, any function with the following attribute
>>> DW_AT_calling_convention (DW_CC_nocall)
>>> indicates this function having signature changed.
>>> pahole can take advantage of this to avoid parameter checking if
>>> DW_AT_calling_convention is not DW_CC_nocall.
>>>
>>> But more importantly, DW_CC_nocall can identify signature-changed functions
>>> and parameters can be checked one-after-another to create the true
>>> signatures. Otherwise, it takes more effort to identify whether a
>>> function has signature changed or not. For example, for funciton
>>> __bpf_kfunc static void bbr_main(struct sock *sk, u32 ack, int flag,
>>> const struct rate_sample *rs) { ... }
>>> and bbr_main() is a callback function in
>>> .cong_control = bbr_main
>>> in 'struct tcp_congestion_ops tcp_bbr_cong_ops'.
>>> In the above bbr_main(...), parameter 'ack' and 'flag' are not used.
>>> The following are some details:
>>>
>>> 0x0a713b8d: DW_TAG_formal_parameter
>>> DW_AT_location (indexed (0x28) loclist = 0x0166d452:
>>> [0xffffffff83e77fd9, 0xffffffff83e78016): DW_OP_reg5 RDI
>>> ...
>>> DW_AT_name ("sk")
>>> DW_AT_type (0x0a6f5b2b "sock *")
>>> ...
>>>
>>> 0x0a713b98: DW_TAG_formal_parameter
>>> DW_AT_name ("ack")
>>> DW_AT_type (0x0a6f58fd "u32")
>>> ...
>>>
>>> 0x0a713ba2: DW_TAG_formal_parameter
>>> DW_AT_name ("flag")
>>> DW_AT_type (0x0a6f57d1 "int")
>>> ...
>>>
>>> 0x0a713bac: DW_TAG_formal_parameter
>>> DW_AT_location (indexed (0x29) loclist = 0x0166d4a8:
>>> [0xffffffff83e77fd9, 0xffffffff83e78016): DW_OP_reg2 RCX
>>> ...
>>> DW_AT_name ("rs")
>>> DW_AT_type (0x0a710da5 "const rate_sample *")
>>> DW_AT_decl_line (1027)
>>>
>>> Some analysis for the above dwarf can conclude that the 'ark' and 'flag'
>>> may be related to RSI and RDX, considering the last one is RCX. Basically this
>>> requires all parameters are available to collectively decide whether the
>>> true signature can be found or not. In such case, DW_CC_nocall can make things
>>> easier as parameter can be checked one after another.
>>>
>>> For a clang built bpf-next kernel, in non-LTO setup, the number of kernel functions
>>> is 69103 and the number of signature changed functions is 875, based on
>>> DW_AT_calling_convention (DW_CC_nocall)
>>> indication.
>> we don't display these stats, right? would be great and probably easy
>> to count different flags and aggregate them
>
> The actual stats will be different depending on kernel code and compiler optimization.
> But I think I can still count them for each commit so people will know
> which change caused how much true signature.
>
I'll send a patch shortly that does kernel build/compare functions for LLVM/clang [1];
currently our pahole CI only covers gcc kernel builds. That will show differences
between pahole next and the current changes in github; that workflow has been handy for
seeing the effects of pahole changes on the set of vmlinux functions.
We should also look at extending pfunct to do more stats; I've got a few patches which
get it to support split BTF and add a manual page. It has some basic stats if I
remember correctly, but it would be nice to extend those at some stage.
[1] https://github.com/alan-maguire/dwarves/actions/runs/23435796365/job/68173414313
>>
>>> Among 875 signature changed functions, after this patch, 495 functions
>>> can have proper true signatures, mostly due to simple dead argument
>>> elimination. The number of remaining functions, which cannot get the
>>> true signature, is 379. They will be addressed in the subsequent commits.
>> after this change I have more functions added (below) and I checked
>> few and they seem ok (w/o DW_CC_nocall)
>
> Most global functions should be okay. But some global functions
> esp. if argument is more than 8 byte (struct type), they may be
> considered as signature change with the current implementation.
>
>>
>> jirka
>>
>>
>> acpi_ex_do_debug_object
>> add_bits
>> amd_pstate_get_mode_string
>> dma_alloc_from_contiguous
>> do_set_pmd
>> dst_destroy
>> find_cpio_data
>> find_microcode_in_initrd
>> ima_write_policy
>> insn_init
>> io_tx_ubuf_complete
>> ip6_protocol_deliver_rcu
>> kvm_tdp_mmu_unmap_gfn_range
>> net_dim_get_def_rx_moderation
>> net_dim_get_def_tx_moderation
>> pinctrl_commit_state
>> string_unescape
>> syscall_copy_user_array
>> tdp_mmu_zap_leafs
>> usb_speed_string
>> __vlan_find_dev_deep_rcu
>> __vxlan_fdb_delete
>> xfs_bmbt_maxrecs
>> xfs_inobt_maxrecs
>> ZSTD_buildSequencesStatistics
>> ZSTD_copyCCtx
>> ZSTD_findFrameSizeInfo
>> ZSTD_get1BlockSummary
>> zstd_get_cparams
>> ZSTD_getCParams
>> ZSTD_getCParamsFromCCtxParams
>> ZSTD_getCParamsFromCDict
>> ZSTD_getCParams_internal
>> zstd_get_params
>> ZSTD_getParams
>
^ permalink raw reply [flat|nested] 20+ messages in thread
* Re: [PATCH dwarves v3 9/9] tests: Add a few clang true signature tests
2026-03-20 19:10 ` [PATCH dwarves v3 9/9] tests: Add a few clang true signature tests Yonghong Song
@ 2026-03-23 15:41 ` Alan Maguire
2026-03-23 19:58 ` Yonghong Song
0 siblings, 1 reply; 20+ messages in thread
From: Alan Maguire @ 2026-03-23 15:41 UTC (permalink / raw)
To: Yonghong Song, Arnaldo Carvalho de Melo, dwarves
Cc: Alexei Starovoitov, Andrii Nakryiko, bpf, kernel-team
On 20/03/2026 19:10, Yonghong Song wrote:
> Three tests are added.
>
> Test 1: VERBOSE=1 ./clang_parm_optimized.sh
> BTF: char * foo(struct t * a, struct t * d);
> DWARF: char * foo(struct t * a, int b, struct t * d);
> where parameber 'b' is unused.
>
> Test 2: VERBOSE=1 ./clang_parm_optimized_stack.sh
> BTF: char * foo(struct t * a, struct t * d);
> DWARF: char * foo(struct t * a, int b1, int b2, int b3, int b4, int b5, int b6, struct t * d);
> where parameters 'b1' to 'b6' are unused.
>
> Test 3: VERBOSE=1 ./clang_parm_aggregate.sh
> BTF: long foo(long a__f1, struct t b, int i);
> DWARF: long foo(struct t a, struct t b, int i);
> where the 'struct t' definition is 'struct t { long f1; long f2; };', and
> a.f2 is not used in the function.
>
> Signed-off-by: Yonghong Song <yonghong.song@linux.dev>
thanks for the tests! Ran this through CI [1] and got a failure on aarch64:
2: clang_parm_aggregate.sh
Validation of BTF encoding of true_signatures.
BTF and DWARF signatures should be different and they are not: BTF: long foo(struct t a, struct t b, int i); ; DWARF long foo(struct t a, struct t b, int i);
Test ./clang_parm_aggregate.sh failed
Test data is in /tmp/clang_parm_aggregate.sh.YC44qj
---
And for a kernel LLVM build (enabled with [2]) we also see:
1: btf_functions.sh
Validation of BTF encoding of functions.
This may take some time.
ERROR: mismatch : BTF 'bool __scm_recv_common(struct sock *, struct msghdr *, struct scm_cookie *);' not found; DWARF ''
Test ./btf_functions.sh failed
Test data is in /tmp/btf_functions.sh.P23ipZ
This test compares BTF and DWARF representations, trying to ensure we see matches
between DWARF function signatures reported by pfunct for both BTF and DWARF. It might
be worth looking to see if we can refine the test here to handle functions with changed
signatures in DWARF, skipping those that have DW_CC_nocall say.
In the above case pfunct is reporting a signature with the flags field omitted. The
original signature looks like this:
static bool __scm_recv_common(struct sock *sk, struct msghdr *msg, struct scm_cookie *scm, int flags);
...so we don't find an equivalent match in DWARF as a result.
[1] https://github.com/alan-maguire/dwarves/actions/runs/23443008554/job/68198951034
[2] https://lore.kernel.org/dwarves/20260323130503.857217-1-alan.maguire@oracle.com/
> ---
> tests/clang_parm_aggregate.sh | 63 +++++++++++++++++++++++
> tests/clang_parm_optimized.sh | 77 +++++++++++++++++++++++++++++
> tests/clang_parm_optimized_stack.sh | 77 +++++++++++++++++++++++++++++
> 3 files changed, 217 insertions(+)
> create mode 100755 tests/clang_parm_aggregate.sh
> create mode 100755 tests/clang_parm_optimized.sh
> create mode 100755 tests/clang_parm_optimized_stack.sh
>
> diff --git a/tests/clang_parm_aggregate.sh b/tests/clang_parm_aggregate.sh
> new file mode 100755
> index 0000000..bf47c8c
> --- /dev/null
> +++ b/tests/clang_parm_aggregate.sh
> @@ -0,0 +1,63 @@
> +#!/bin/bash
> +# SPDX-License-Identifier: GPL-2.0-only
> +
> +source test_lib.sh
> +
> +outdir=$(make_tmpdir)
> +
> +# Comment this out to save test data.
> +trap cleanup EXIT
> +
> +title_log "Validation of BTF encoding of true_signatures."
> +
> +clang_true="${outdir}/clang_true"
> +CC=$(which clang 2>/dev/null)
> +
> +if [[ -z "$CC" ]]; then
> + info_log "skip: clang not available"
> + test_skip
> +fi
> +
> +cat > ${clang_true}.c << EOF
> +struct t { long f1; long f2; };
> +__attribute__((noinline)) static long foo(struct t a, struct t b, int i)
> +{
> + return a.f1 + b.f1 + b.f2 + i;
> +}
> +
> +struct t p1, p2;
> +int i;
> +int main()
> +{
> + return (int)foo(p1, p2, i);
> +}
> +EOF
> +
> +CFLAGS="$CFLAGS -g -O2"
> +${CC} ${CFLAGS} -o $clang_true ${clang_true}.c
> +if [[ $? -ne 0 ]]; then
> + error_log "Could not compile ${clang_true}.c"
> + test_fail
> +fi
> +LLVM_OBJCOPY=objcopy pahole -J --btf_features=+true_signature $clang_true
> +if [[ $? -ne 0 ]]; then
> + error_log "Could not encode BTF for $clang_true"
> + test_fail
> +fi
> +
> +btf_optimized=$(pfunct --all --format_path=btf $clang_true |grep "foo")
> +if [[ -z "$btf_optimized" ]]; then
> + info_log "skip: no optimizations applied."
> + test_skip
> +fi
> +
> +btf_cmp=$btf_optimized
> +dwarf=$(pfunct --all $clang_true |grep "foo")
> +
> +verbose_log "BTF: $btf_optimized DWARF: $dwarf"
> +
> +if [[ "$btf_cmp" == "$dwarf" ]]; then
> + error_log "BTF and DWARF signatures should be different and they are not: BTF: $btf_optimized ; DWARF $dwarf"
> + test_fail
> +fi
> +test_pass
> diff --git a/tests/clang_parm_optimized.sh b/tests/clang_parm_optimized.sh
> new file mode 100755
> index 0000000..379e6d5
> --- /dev/null
> +++ b/tests/clang_parm_optimized.sh
> @@ -0,0 +1,77 @@
> +#!/bin/bash
> +# SPDX-License-Identifier: GPL-2.0-only
> +
> +source test_lib.sh
> +
> +outdir=$(make_tmpdir)
> +
> +# Comment this out to save test data.
> +trap cleanup EXIT
> +
> +title_log "Validation of BTF encoding of true_signatures."
> +
> +clang_true="${outdir}/clang_true"
> +CC=$(which clang 2>/dev/null)
> +
> +if [[ -z "$CC" ]]; then
> + info_log "skip: clang not available"
> + test_skip
> +fi
> +
> +cat > ${clang_true}.c << EOF
> +struct t { int a; };
> +__attribute__((noinline)) char *tar(struct t *a, struct t *d)
> +{
> + if (a->a == d->a)
> + return (char *)10;
> + else
> + return (char *)0;
> +}
> +
> +__attribute__((noinline)) static char * foo(struct t *a, int b, struct t *d)
> +{
> + return tar(a, d);
> +}
> +
> +__attribute__((noinline)) char *bar(struct t *a, struct t *d)
> +{
> + return foo(a, 1, d);
> +}
> +
> +struct t p1, p2;
> +int main()
> +{
> + return !!bar(&p1, &p2);
> +}
> +EOF
> +
> +CFLAGS="$CFLAGS -g -O2"
> +${CC} ${CFLAGS} -o $clang_true ${clang_true}.c
> +if [[ $? -ne 0 ]]; then
> + error_log "Could not compile ${clang_true}.c"
> + test_fail
> +fi
> +LLVM_OBJCOPY=objcopy pahole -J --btf_features=+true_signature $clang_true
> +if [[ $? -ne 0 ]]; then
> + error_log "Could not encode BTF for $clang_true"
> + test_fail
> +fi
> +
> +btf_optimized=$(pfunct --all --format_path=btf $clang_true |grep "foo")
> +if [[ -z "$btf_optimized" ]]; then
> + info_log "skip: no optimizations applied."
> + test_skip
> +fi
> +
> +btf_cmp=$btf_optimized
> +dwarf=$(pfunct --all $clang_true |grep "foo")
> +
> +if [[ -n "$VERBOSE" ]]; then
> + printf " BTF: %s DWARF: %s\n" "$btf_optimized" "$dwarf"
> +fi
> +
> +if [[ "$btf_cmp" == "$dwarf" ]]; then
> + error_log "BTF and DWARF signatures should be different and they are not: BTF: $btf_optimized ; DWARF $dwarf"
> + test_fail
> +fi
> +test_pass
> diff --git a/tests/clang_parm_optimized_stack.sh b/tests/clang_parm_optimized_stack.sh
> new file mode 100755
> index 0000000..8638af7
> --- /dev/null
> +++ b/tests/clang_parm_optimized_stack.sh
> @@ -0,0 +1,77 @@
> +#!/bin/bash
> +# SPDX-License-Identifier: GPL-2.0-only
> +
> +source test_lib.sh
> +
> +outdir=$(make_tmpdir)
> +
> +# Comment this out to save test data.
> +trap cleanup EXIT
> +
> +title_log "Validation of BTF encoding of true_signatures."
> +
> +clang_true="${outdir}/clang_true"
> +CC=$(which clang 2>/dev/null)
> +
> +if [[ -z "$CC" ]]; then
> + info_log "skip: clang not available"
> + test_skip
> +fi
> +
> +cat > ${clang_true}.c << EOF
> +struct t { int a; };
> +__attribute__((noinline)) char *tar(struct t *a, struct t *d)
> +{
> + if (a->a == d->a)
> + return (char *)10;
> + else
> + return (char *)0;
> +}
> +
> +__attribute__((noinline)) static char * foo(struct t *a, int b1, int b2, int b3, int b4, int b5, int b6, struct t *d)
> +{
> + return tar(a, d);
> +}
> +
> +__attribute__((noinline)) char *bar(struct t *a, struct t *d)
> +{
> + return foo(a, 1, 2, 3, 4, 5, 6, d);
> +}
> +
> +struct t p1, p2;
> +int main()
> +{
> + return !!bar(&p1, &p2);
> +}
> +EOF
> +
> +CFLAGS="$CFLAGS -g -O2"
> +${CC} ${CFLAGS} -o $clang_true ${clang_true}.c
> +if [[ $? -ne 0 ]]; then
> + error_log "Could not compile ${clang_true}.c"
> + test_fail
> +fi
> +LLVM_OBJCOPY=objcopy pahole -J --btf_features=+true_signature $clang_true
> +if [[ $? -ne 0 ]]; then
> + error_log "Could not encode BTF for $clang_true"
> + test_fail
> +fi
> +
> +btf_optimized=$(pfunct --all --format_path=btf $clang_true |grep "foo")
> +if [[ -z "$btf_optimized" ]]; then
> + info_log "skip: no optimizations applied."
> + test_skip
> +fi
> +
> +btf_cmp=$btf_optimized
> +dwarf=$(pfunct --all $clang_true |grep "foo")
> +
> +if [[ -n "$VERBOSE" ]]; then
> + printf " BTF: %s DWARF: %s\n" "$btf_optimized" "$dwarf"
> +fi
> +
> +if [[ "$btf_cmp" == "$dwarf" ]]; then
> + error_log "BTF and DWARF signatures should be different and they are not: BTF: $btf_optimized ; DWARF $dwarf"
> + test_fail
> +fi
> +test_pass
^ permalink raw reply [flat|nested] 20+ messages in thread
* Re: [PATCH dwarves v3 1/9] dwarf_loader: Reduce parameter checking with clang DW_AT_calling_convention attr
2026-03-23 12:56 ` Alan Maguire
@ 2026-03-23 18:32 ` Yonghong Song
0 siblings, 0 replies; 20+ messages in thread
From: Yonghong Song @ 2026-03-23 18:32 UTC (permalink / raw)
To: Alan Maguire, Jiri Olsa
Cc: Arnaldo Carvalho de Melo, dwarves, Alexei Starovoitov,
Andrii Nakryiko, bpf, kernel-team
On 3/23/26 5:56 AM, Alan Maguire wrote:
> On 22/03/2026 17:36, Yonghong Song wrote:
>>
>> On 3/21/26 4:10 PM, Jiri Olsa wrote:
>>> On Fri, Mar 20, 2026 at 12:09:22PM -0700, Yonghong Song wrote:
>>>> Currently every function is checked for its parameters to identify whether
>>>> the signature changed or not. If signature indeed changed, pahole may do
>>>> some adjustment for parameters for true signatures.
>>>>
>>>> In clang, any function with the following attribute
>>>> DW_AT_calling_convention (DW_CC_nocall)
>>>> indicates this function having signature changed.
>>>> pahole can take advantage of this to avoid parameter checking if
>>>> DW_AT_calling_convention is not DW_CC_nocall.
>>>>
>>>> But more importantly, DW_CC_nocall can identify signature-changed functions
>>>> and parameters can be checked one-after-another to create the true
>>>> signatures. Otherwise, it takes more effort to identify whether a
>>>> function has signature changed or not. For example, for funciton
>>>> __bpf_kfunc static void bbr_main(struct sock *sk, u32 ack, int flag,
>>>> const struct rate_sample *rs) { ... }
>>>> and bbr_main() is a callback function in
>>>> .cong_control = bbr_main
>>>> in 'struct tcp_congestion_ops tcp_bbr_cong_ops'.
>>>> In the above bbr_main(...), parameter 'ack' and 'flag' are not used.
>>>> The following are some details:
>>>>
>>>> 0x0a713b8d: DW_TAG_formal_parameter
>>>> DW_AT_location (indexed (0x28) loclist = 0x0166d452:
>>>> [0xffffffff83e77fd9, 0xffffffff83e78016): DW_OP_reg5 RDI
>>>> ...
>>>> DW_AT_name ("sk")
>>>> DW_AT_type (0x0a6f5b2b "sock *")
>>>> ...
>>>>
>>>> 0x0a713b98: DW_TAG_formal_parameter
>>>> DW_AT_name ("ack")
>>>> DW_AT_type (0x0a6f58fd "u32")
>>>> ...
>>>>
>>>> 0x0a713ba2: DW_TAG_formal_parameter
>>>> DW_AT_name ("flag")
>>>> DW_AT_type (0x0a6f57d1 "int")
>>>> ...
>>>>
>>>> 0x0a713bac: DW_TAG_formal_parameter
>>>> DW_AT_location (indexed (0x29) loclist = 0x0166d4a8:
>>>> [0xffffffff83e77fd9, 0xffffffff83e78016): DW_OP_reg2 RCX
>>>> ...
>>>> DW_AT_name ("rs")
>>>> DW_AT_type (0x0a710da5 "const rate_sample *")
>>>> DW_AT_decl_line (1027)
>>>>
>>>> Some analysis for the above dwarf can conclude that the 'ark' and 'flag'
>>>> may be related to RSI and RDX, considering the last one is RCX. Basically this
>>>> requires all parameters are available to collectively decide whether the
>>>> true signature can be found or not. In such case, DW_CC_nocall can make things
>>>> easier as parameter can be checked one after another.
>>>>
>>>> For a clang built bpf-next kernel, in non-LTO setup, the number of kernel functions
>>>> is 69103 and the number of signature changed functions is 875, based on
>>>> DW_AT_calling_convention (DW_CC_nocall)
>>>> indication.
>>> we don't display these stats, right? would be great and probably easy
>>> to count different flags and aggregate them
>> The actual stats will be different depending on kernel code and compiler optimization.
>> But I think I can still count them for each commit so people will know
>> which change caused how much true signature.
>>
> I'll send a patch shortly that does kernel build/compare functions for LLVM/clang [1];
> currently our pahole CI only covers gcc kernel builds. That will show differences
> between pahole next and the current changes in github; that workflow has been handy for
> seeing the effects of pahole changes on the set of vmlinux functions.
>
> We should also look at extending pfunct to do more stats; I've got a few patches which
> get it to support split BTF and add a manual page. It has some basic stats if I
> remember correctly, but it would be nice to extend those at some stage.
>
> [1] https://github.com/alan-maguire/dwarves/actions/runs/23435796365/job/68173414313
Thanks for adding llvm test support in github. This definitely helpful.
I will try to have a few more coverages from llvm side.
>
>>>> Among 875 signature changed functions, after this patch, 495 functions
>>>> can have proper true signatures, mostly due to simple dead argument
>>>> elimination. The number of remaining functions, which cannot get the
>>>> true signature, is 379. They will be addressed in the subsequent commits.
>>> after this change I have more functions added (below) and I checked
>>> few and they seem ok (w/o DW_CC_nocall)
>> Most global functions should be okay. But some global functions
>> esp. if argument is more than 8 byte (struct type), they may be
>> considered as signature change with the current implementation.
>>
>>> jirka
>>>
>>>
>>> acpi_ex_do_debug_object
>>> add_bits
>>> amd_pstate_get_mode_string
>>> dma_alloc_from_contiguous
>>> do_set_pmd
>>> dst_destroy
>>> find_cpio_data
>>> find_microcode_in_initrd
>>> ima_write_policy
>>> insn_init
>>> io_tx_ubuf_complete
>>> ip6_protocol_deliver_rcu
>>> kvm_tdp_mmu_unmap_gfn_range
>>> net_dim_get_def_rx_moderation
>>> net_dim_get_def_tx_moderation
>>> pinctrl_commit_state
>>> string_unescape
>>> syscall_copy_user_array
>>> tdp_mmu_zap_leafs
>>> usb_speed_string
>>> __vlan_find_dev_deep_rcu
>>> __vxlan_fdb_delete
>>> xfs_bmbt_maxrecs
>>> xfs_inobt_maxrecs
>>> ZSTD_buildSequencesStatistics
>>> ZSTD_copyCCtx
>>> ZSTD_findFrameSizeInfo
>>> ZSTD_get1BlockSummary
>>> zstd_get_cparams
>>> ZSTD_getCParams
>>> ZSTD_getCParamsFromCCtxParams
>>> ZSTD_getCParamsFromCDict
>>> ZSTD_getCParams_internal
>>> zstd_get_params
>>> ZSTD_getParams
^ permalink raw reply [flat|nested] 20+ messages in thread
* Re: [PATCH dwarves v3 9/9] tests: Add a few clang true signature tests
2026-03-23 15:41 ` Alan Maguire
@ 2026-03-23 19:58 ` Yonghong Song
0 siblings, 0 replies; 20+ messages in thread
From: Yonghong Song @ 2026-03-23 19:58 UTC (permalink / raw)
To: Alan Maguire, Arnaldo Carvalho de Melo, dwarves
Cc: Alexei Starovoitov, Andrii Nakryiko, bpf, kernel-team
On 3/23/26 8:41 AM, Alan Maguire wrote:
> On 20/03/2026 19:10, Yonghong Song wrote:
>> Three tests are added.
>>
>> Test 1: VERBOSE=1 ./clang_parm_optimized.sh
>> BTF: char * foo(struct t * a, struct t * d);
>> DWARF: char * foo(struct t * a, int b, struct t * d);
>> where parameber 'b' is unused.
>>
>> Test 2: VERBOSE=1 ./clang_parm_optimized_stack.sh
>> BTF: char * foo(struct t * a, struct t * d);
>> DWARF: char * foo(struct t * a, int b1, int b2, int b3, int b4, int b5, int b6, struct t * d);
>> where parameters 'b1' to 'b6' are unused.
>>
>> Test 3: VERBOSE=1 ./clang_parm_aggregate.sh
>> BTF: long foo(long a__f1, struct t b, int i);
>> DWARF: long foo(struct t a, struct t b, int i);
>> where the 'struct t' definition is 'struct t { long f1; long f2; };', and
>> a.f2 is not used in the function.
>>
>> Signed-off-by: Yonghong Song <yonghong.song@linux.dev>
> thanks for the tests! Ran this through CI [1] and got a failure on aarch64:
>
> 2: clang_parm_aggregate.sh
> Validation of BTF encoding of true_signatures.
> BTF and DWARF signatures should be different and they are not: BTF: long foo(struct t a, struct t b, int i); ; DWARF long foo(struct t a, struct t b, int i);
> Test ./clang_parm_aggregate.sh failed
> Test data is in /tmp/clang_parm_aggregate.sh.YC44qj
Thanks for spotting this. I forgot to verify it on aarch64.
For x86, we have:
0x00000041: DW_TAG_subprogram
DW_AT_low_pc (0x0000000000000020)
DW_AT_high_pc (0x000000000000002d)
DW_AT_frame_base (DW_OP_reg7 RSP)
DW_AT_call_all_calls (true)
DW_AT_name ("foo")
DW_AT_decl_file ("/home/yhs/tmp/tmp4/t.c")
DW_AT_decl_line (2)
DW_AT_prototyped (true)
DW_AT_calling_convention (DW_CC_nocall)
DW_AT_type (0x00000094 "long")
0x00000051: DW_TAG_formal_parameter
DW_AT_location (DW_OP_reg5 RDI, DW_OP_piece 0x8)
DW_AT_name ("a")
DW_AT_decl_file ("/home/yhs/tmp/tmp4/t.c")
DW_AT_decl_line (2)
DW_AT_type (0x0000007c "t")
0x0000005d: DW_TAG_formal_parameter
DW_AT_location (indexed (0x0) loclist = 0x00000010:
[0x0000000000000020, 0x0000000000000023): DW_OP_reg4 RSI, DW_OP_piece 0x8, DW_OP_reg1 RDX, DW_OP_piece 0x8
[0x0000000000000023, 0x000000000000002d): DW_OP_piece 0x8, DW_OP_reg1 RDX, DW_OP_piece 0x8)
DW_AT_name ("b")
DW_AT_decl_file ("/home/yhs/tmp/tmp4/t.c")
DW_AT_decl_line (2)
DW_AT_type (0x0000007c "t")
0x00000066: DW_TAG_formal_parameter
DW_AT_location (DW_OP_reg2 RCX)
DW_AT_name ("i")
DW_AT_decl_file ("/home/yhs/tmp/tmp4/t.c")
DW_AT_decl_line (2)
DW_AT_type (0x00000027 "int")
0x00000070: NULL
So for x84, we can find true signature.
For aarch64:
0x00000041: DW_TAG_subprogram
DW_AT_low_pc (0x0000000000000034)
DW_AT_high_pc (0x0000000000000044)
DW_AT_frame_base (DW_OP_reg31 WSP)
DW_AT_call_all_calls (true)
DW_AT_name ("foo")
DW_AT_decl_file ("/home/yhs/tmp/t.c")
DW_AT_decl_line (2)
DW_AT_prototyped (true)
DW_AT_type (0x00000090 "long")
0x00000050: DW_TAG_formal_parameter
DW_AT_location (indexed (0x0) loclist = 0x00000014:
[0x0000000000000034, 0x0000000000000040): DW_OP_reg0 W0, DW_OP_piece 0x8)
DW_AT_name ("a")
DW_AT_decl_file ("/home/yhs/tmp/t.c")
DW_AT_decl_line (2)
DW_AT_type (0x00000078 "t")
0x00000059: DW_TAG_formal_parameter
DW_AT_location (indexed (0x1) loclist = 0x0000001c:
[0x0000000000000034, 0x0000000000000044): DW_OP_reg2 W2, DW_OP_piece 0x8, DW_OP_reg3 W3, DW_OP_piece 0x8)
DW_AT_name ("b")
DW_AT_decl_file ("/home/yhs/tmp/t.c")
DW_AT_decl_line (2)
DW_AT_type (0x00000078 "t")
0x00000062: DW_TAG_formal_parameter
DW_AT_location (DW_OP_reg4 W4)
DW_AT_name ("i")
DW_AT_decl_file ("/home/yhs/tmp/t.c")
DW_AT_decl_line (2)
DW_AT_type (0x00000027 "int")
0x0000006c: NULL
In this case, the parameter 'a' only uses the first 8 byte which encoded into W0. The argument 'b'
uses W2/W3. For this particular case, the original signature should be used. I will try to find a
way to resolve this.
> ---
>
> And for a kernel LLVM build (enabled with [2]) we also see:
>
> 1: btf_functions.sh
> Validation of BTF encoding of functions.
> This may take some time.
> ERROR: mismatch : BTF 'bool __scm_recv_common(struct sock *, struct msghdr *, struct scm_cookie *);' not found; DWARF ''
> Test ./btf_functions.sh failed
> Test data is in /tmp/btf_functions.sh.P23ipZ
>
> This test compares BTF and DWARF representations, trying to ensure we see matches
> between DWARF function signatures reported by pfunct for both BTF and DWARF. It might
> be worth looking to see if we can refine the test here to handle functions with changed
> signatures in DWARF, skipping those that have DW_CC_nocall say.
>
> In the above case pfunct is reporting a signature with the flags field omitted. The
> original signature looks like this:
>
> static bool __scm_recv_common(struct sock *sk, struct msghdr *msg, struct scm_cookie *scm, int flags);
>
> ...so we don't find an equivalent match in DWARF as a result.
Currently, without +true_signature flag, clang may still generate true signatures
by filtering the dead arguments which are at the end of function parameters.
I think we should require +true_signagure flag to do this.
I will fix this. Thanks for spotting.
>
> [1] https://github.com/alan-maguire/dwarves/actions/runs/23443008554/job/68198951034
> [2] https://lore.kernel.org/dwarves/20260323130503.857217-1-alan.maguire@oracle.com/
>
>> ---
>> tests/clang_parm_aggregate.sh | 63 +++++++++++++++++++++++
>> tests/clang_parm_optimized.sh | 77 +++++++++++++++++++++++++++++
>> tests/clang_parm_optimized_stack.sh | 77 +++++++++++++++++++++++++++++
>> 3 files changed, 217 insertions(+)
>> create mode 100755 tests/clang_parm_aggregate.sh
>> create mode 100755 tests/clang_parm_optimized.sh
>> create mode 100755 tests/clang_parm_optimized_stack.sh
>>
>> diff --git a/tests/clang_parm_aggregate.sh b/tests/clang_parm_aggregate.sh
>> new file mode 100755
>> index 0000000..bf47c8c
>> --- /dev/null
>> +++ b/tests/clang_parm_aggregate.sh
>> @@ -0,0 +1,63 @@
>> +#!/bin/bash
>> +# SPDX-License-Identifier: GPL-2.0-only
>> +
>> +source test_lib.sh
>> +
>> +outdir=$(make_tmpdir)
>> +
>> +# Comment this out to save test data.
>> +trap cleanup EXIT
>> +
>> +title_log "Validation of BTF encoding of true_signatures."
>> +
>> +clang_true="${outdir}/clang_true"
>> +CC=$(which clang 2>/dev/null)
>> +
>> +if [[ -z "$CC" ]]; then
>> + info_log "skip: clang not available"
>> + test_skip
>> +fi
>> +
>> +cat > ${clang_true}.c << EOF
>> +struct t { long f1; long f2; };
>> +__attribute__((noinline)) static long foo(struct t a, struct t b, int i)
>> +{
>> + return a.f1 + b.f1 + b.f2 + i;
>> +}
>> +
>> +struct t p1, p2;
>> +int i;
>> +int main()
>> +{
>> + return (int)foo(p1, p2, i);
>> +}
>> +EOF
>> +
>> +CFLAGS="$CFLAGS -g -O2"
>> +${CC} ${CFLAGS} -o $clang_true ${clang_true}.c
>> +if [[ $? -ne 0 ]]; then
>> + error_log "Could not compile ${clang_true}.c"
>> + test_fail
>> +fi
>> +LLVM_OBJCOPY=objcopy pahole -J --btf_features=+true_signature $clang_true
>> +if [[ $? -ne 0 ]]; then
>> + error_log "Could not encode BTF for $clang_true"
>> + test_fail
>> +fi
>> +
>> +btf_optimized=$(pfunct --all --format_path=btf $clang_true |grep "foo")
>> +if [[ -z "$btf_optimized" ]]; then
>> + info_log "skip: no optimizations applied."
>> + test_skip
>> +fi
>> +
>> +btf_cmp=$btf_optimized
>> +dwarf=$(pfunct --all $clang_true |grep "foo")
>> +
>> +verbose_log "BTF: $btf_optimized DWARF: $dwarf"
>> +
>> +if [[ "$btf_cmp" == "$dwarf" ]]; then
>> + error_log "BTF and DWARF signatures should be different and they are not: BTF: $btf_optimized ; DWARF $dwarf"
>> + test_fail
>> +fi
>> +test_pass
[...]
^ permalink raw reply [flat|nested] 20+ messages in thread
end of thread, other threads:[~2026-03-23 19:58 UTC | newest]
Thread overview: 20+ messages (download: mbox.gz follow: Atom feed
-- links below jump to the message on this page --
2026-03-20 19:09 [PATCH dwarves v3 0/9] pahole: Encode true signatures in kernel BTF Yonghong Song
2026-03-20 19:09 ` [PATCH dwarves v3 1/9] dwarf_loader: Reduce parameter checking with clang DW_AT_calling_convention attr Yonghong Song
2026-03-21 23:10 ` Jiri Olsa
2026-03-22 17:36 ` Yonghong Song
2026-03-23 12:56 ` Alan Maguire
2026-03-23 18:32 ` Yonghong Song
2026-03-20 19:09 ` [PATCH dwarves v3 2/9] dwarf_loader: Handle signatures with dead arguments Yonghong Song
2026-03-21 23:10 ` Jiri Olsa
2026-03-22 18:03 ` Yonghong Song
2026-03-20 19:09 ` [PATCH dwarves v3 3/9] dwarf_loader: Refactor initial ret -1 to be macro PARM_DEFAULT_FAIL Yonghong Song
2026-03-20 19:09 ` [PATCH dwarves v3 4/9] dwarf_laoder: Handle locations with DW_OP_fbreg Yonghong Song
2026-03-20 19:09 ` [PATCH dwarves v3 5/9] dwarf_loader: Change exprlen checking condition in parameter__reg() Yonghong Song
2026-03-20 19:09 ` [PATCH dwarves v3 6/9] dwarf_loader: Detect optimized parameters with locations having constant values Yonghong Song
2026-03-20 19:09 ` [PATCH dwarves v3 7/9] dwarf_loader: Handle expression lists Yonghong Song
2026-03-21 23:10 ` Jiri Olsa
2026-03-22 18:33 ` Yonghong Song
2026-03-20 19:09 ` [PATCH dwarves v3 8/9] btf_encoder: Handle optimized parameter properly Yonghong Song
2026-03-20 19:10 ` [PATCH dwarves v3 9/9] tests: Add a few clang true signature tests Yonghong Song
2026-03-23 15:41 ` Alan Maguire
2026-03-23 19:58 ` Yonghong Song
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