[PATCH V3 13/14] tools/perf: Add support for global_die to capture name of variable in case of register defined variable

Athira Rajeev
2024-06-01T06:10:53Z

In case of register defined variable (found using
find_data_type_global_reg), if the type of variable happens to be base
type (example, long unsigned int), perf report captures it as:

12.85% long unsigned int long unsigned int +0 (no field)

The above data type is actually referring to samples captured while
accessing "r1" which represents current stack pointer in powerpc.
register void *__stack_pointer asm("r1");

The dwarf debug contains this as:

<<>>
<1><18dd772>: Abbrev Number: 129 (DW_TAG_variable)
<18dd774> DW_AT_name : (indirect string, offset: 0x11ba): current_stack_pointer
<18dd778> DW_AT_decl_file : 51
<18dd779> DW_AT_decl_line : 1468
<18dd77b> DW_AT_decl_column : 24
<18dd77c> DW_AT_type : <0x18da5cd>
<18dd780> DW_AT_external : 1
<18dd780> DW_AT_location : 1 byte block: 51 (DW_OP_reg1 (r1))

where 18da5cd is:

<1><18da5cd>: Abbrev Number: 47 (DW_TAG_base_type)
<18da5ce> DW_AT_byte_size : 8
<18da5cf> DW_AT_encoding : 7 (unsigned)
<18da5d0> DW_AT_name : (indirect string, offset: 0x55c7): long unsigned int
<<>>

To make it more clear to the user, capture the DW_AT_name of the
variable and save it as part of Dwarf_Global. Dwarf_Global is used so
that it can be used and retrieved while presenting the result.

Update "dso__findnew_data_type" function to set "var_name" if
variable name is set as part of Dwarf_Global. Updated
"hist_entry__typeoff_snprintf" to print var_name if it is set.
With the changes, along with "long unsigned int" report also says the
variable name as current_stack_pointer

Snippet of result:

12.85% long unsigned int long unsigned int +0 (current_stack_pointer)
4.68% struct paca_struct struct paca_struct +2312 (__current)
4.57% struct paca_struct struct paca_struct +2354 (irq_soft_mask)

Signed-off-by: Athira Rajeev <atrajeev@linux.vnet.ibm.com>
---
tools/perf/util/annotate-data.c | 30 ++++++++++++++++++++++++------
tools/perf/util/dwarf-aux.c | 1 +
tools/perf/util/dwarf-aux.h | 1 +
tools/perf/util/sort.c | 7 +++++--
4 files changed, 31 insertions(+), 8 deletions(-)

diff --git a/tools/perf/util/annotate-data.c b/tools/perf/util/annotate-data.c
index 82232f2d8e16..2bce522304f4 100644
--- a/tools/perf/util/annotate-data.c
+++ b/tools/perf/util/annotate-data.c
@@ -268,23 +268,32 @@ static void delete_members(struct annotated_member *member)
}

static struct annotated_data_type *dso__findnew_data_type(struct dso *dso,
- Dwarf_Die *type_die)
+ Dwarf_Die *type_die, Dwarf_Global *global_die)
{
struct annotated_data_type *result = NULL;
struct annotated_data_type key;
struct rb_node *node;
struct strbuf sb;
+ struct strbuf sb_var_name;
char *type_name;
+ char *var_name;
Dwarf_Word size;

strbuf_init(&sb, 32);
+ strbuf_init(&sb_var_name, 32);
if (die_get_typename_from_type(type_die, &sb) < 0)
strbuf_add(&sb, "(unknown type)", 14);
+ if (global_die->name) {
+ strbuf_addstr(&sb_var_name, global_die->name);
+ var_name = strbuf_detach(&sb_var_name, NULL);
+ }
type_name = strbuf_detach(&sb, NULL);
dwarf_aggregate_size(type_die, &size);

/* Check existing nodes in dso->data_types tree */
key.self.type_name = type_name;
+ if (global_die->name)
+ key.self.var_name = var_name;
key.self.size = size;
node = rb_find(&key, dso__data_types(dso), data_type_cmp);
if (node) {
@@ -301,6 +310,8 @@ static struct annotated_data_type *dso__findnew_data_type(struct dso *dso,
}

result->self.type_name = type_name;
+ if (global_die->name)
+ result->self.var_name = var_name;
result->self.size = size;
INIT_LIST_HEAD(&result->self.children);

@@ -1178,7 +1189,7 @@ static int find_data_type_block(struct data_loc_info *dloc,
* cu_die and match with reg to identify data type die.
*/
static int find_data_type_global_reg(struct data_loc_info *dloc, int reg, Dwarf_Die *cu_die,
- Dwarf_Die *type_die)
+ Dwarf_Die *type_die, Dwarf_Global *global_die)
{
Dwarf_Die vr_die;
int ret = -1;
@@ -1190,8 +1201,11 @@ static int find_data_type_global_reg(struct data_loc_info *dloc, int reg, Dwarf_
if (dwarf_offdie(dloc->di->dbg, var_types->die_off, &vr_die)) {
if (die_get_real_type(&vr_die, type_die) == NULL) {
dloc->type_offset = 0;
+ global_die->name = var_types->name;
dwarf_offdie(dloc->di->dbg, var_types->die_off, type_die);
}
+ global_die->die_offset = (long)dwarf_dieoffset(type_die);
+ global_die->cu_offset = (long)dwarf_dieoffset(cu_die);
pr_debug_type_name(type_die, TSR_KIND_TYPE);
ret = 0;
pr_debug_dtp("found by CU for %s (die:%#lx)\n",
@@ -1205,7 +1219,8 @@ static int find_data_type_global_reg(struct data_loc_info *dloc, int reg, Dwarf_
}

/* The result will be saved in @type_die */
-static int find_data_type_die(struct data_loc_info *dloc, Dwarf_Die *type_die)
+static int find_data_type_die(struct data_loc_info *dloc, Dwarf_Die *type_die,
+ Dwarf_Global *global_die)
{
struct annotated_op_loc *loc = dloc->op;
Dwarf_Die cu_die, var_die;
@@ -1219,6 +1234,8 @@ static int find_data_type_die(struct data_loc_info *dloc, Dwarf_Die *type_die)
u64 pc;
char buf[64];

+ memset(global_die, 0, sizeof(Dwarf_Global));
+
if (dloc->op->multi_regs)
snprintf(buf, sizeof(buf), "reg%d, reg%d", dloc->op->reg1, dloc->op->reg2);
else if (dloc->op->reg1 == DWARF_REG_PC)
@@ -1252,7 +1269,7 @@ static int find_data_type_die(struct data_loc_info *dloc, Dwarf_Die *type_die)
dwarf_diename(&cu_die), (long)dwarf_dieoffset(&cu_die));

if (loc->reg_type == DWARF_REG_GLOBAL) {
- ret = find_data_type_global_reg(dloc, reg, &cu_die, type_die);
+ ret = find_data_type_global_reg(dloc, reg, &cu_die, type_die, global_die);
if (!ret)
goto out;
}
@@ -1388,6 +1405,7 @@ struct annotated_data_type *find_data_type(struct data_loc_info *dloc)
struct annotated_data_type *result = NULL;
struct dso *dso = map__dso(dloc->ms->map);
Dwarf_Die type_die;
+ Dwarf_Global global_die;

dloc->di = debuginfo__new(dso__long_name(dso));
if (dloc->di == NULL) {
@@ -1403,10 +1421,10 @@ struct annotated_data_type *find_data_type(struct data_loc_info *dloc)

dloc->fbreg = -1;

- if (find_data_type_die(dloc, &type_die) < 0)
+ if (find_data_type_die(dloc, &type_die, &global_die) < 0)
goto out;

- result = dso__findnew_data_type(dso, &type_die);
+ result = dso__findnew_data_type(dso, &type_die, &global_die);

out:
debuginfo__delete(dloc->di);
diff --git a/tools/perf/util/dwarf-aux.c b/tools/perf/util/dwarf-aux.c
index 44ef968a7ad3..9e61ff326651 100644
--- a/tools/perf/util/dwarf-aux.c
+++ b/tools/perf/util/dwarf-aux.c
@@ -1610,6 +1610,7 @@ static int __die_collect_vars_cb(Dwarf_Die *die_mem, void *arg)
vt->reg = reg_from_dwarf_op(ops);
vt->offset = offset_from_dwarf_op(ops);
vt->next = *var_types;
+ vt->name = dwarf_diename(die_mem);
*var_types = vt;

return DIE_FIND_CB_SIBLING;
diff --git a/tools/perf/util/dwarf-aux.h b/tools/perf/util/dwarf-aux.h
index 24446412b869..406a5b1e269b 100644
--- a/tools/perf/util/dwarf-aux.h
+++ b/tools/perf/util/dwarf-aux.h
@@ -146,6 +146,7 @@ struct die_var_type {
u64 addr;
int reg;
int offset;
+ const char *name;
};

/* Return type info of a member at offset */
diff --git a/tools/perf/util/sort.c b/tools/perf/util/sort.c
index cd39ea972193..535ca19a23fd 100644
--- a/tools/perf/util/sort.c
+++ b/tools/perf/util/sort.c
@@ -2305,9 +2305,12 @@ static int hist_entry__typeoff_snprintf(struct hist_entry *he, char *bf,
char buf[4096];

buf[0] = '\0';
- if (list_empty(&he_type->self.children))
+ if (list_empty(&he_type->self.children)) {
snprintf(buf, sizeof(buf), "no field");
- else
+ if (he_type->self.var_name)
+ strcpy(buf, he_type->self.var_name);
+
+ } else
fill_member_name(buf, sizeof(buf), &he_type->self,
he->mem_type_off, true);
buf[4095] = '\0';
--
2.43.0