[PATCH v9.1 06/11] tracing/probes: Support function parameters if BTF is available

Masami Hiramatsu (Google)
2023-05-02T02:18:50Z

Support function or tracepoint parameters by name if BTF support is enabled
and the event is for function entry (this feature can be used with kprobe-
events, fprobe-events and tracepoint probe events.)

Note that the BTF variable syntax does not require a prefix. If it starts
with an alphabetic character or an underscore ('_') without a prefix like
'$' and '%', it is considered as a BTF variable.
If you specify only the BTF variable name, the argument name will also
be the same name instead of 'arg*'.

# echo 'p vfs_read count pos' >> dynamic_events
# echo 'f vfs_write count pos' >> dynamic_events
# echo 't sched_overutilized_tp rd overutilized' >> dynamic_events
# cat dynamic_events
p:kprobes/p_vfs_read_0 vfs_read count=count pos=pos
f:fprobes/vfs_write__entry vfs_write count=count pos=pos
t:tracepoints/sched_overutilized_tp sched_overutilized_tp rd=rd overutilized=overutilized

Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Reviewed-by: Alan Maguire <alan.maguire@oracle.com>
Tested-by: Alan Maguire <alan.maguire@oracle.com>
---
Changes in v8:
- Update Kconfig help description.
Changes in v7:
- Add BTF_KIND_ENUM64 support
- Fix to check the ERR_PTR() type return value of bpf_get_btf_vmlinux().
Changes in v6:
- update patch description.
- use bpf_get_btf_vmlinux() instead of btf_parse_vmlinux().
---
kernel/trace/Kconfig | 12 +++
kernel/trace/trace.c | 4 +
kernel/trace/trace_fprobe.c | 49 +++++++----
kernel/trace/trace_kprobe.c | 12 +--
kernel/trace/trace_probe.c | 191 +++++++++++++++++++++++++++++++++++++++++++
kernel/trace/trace_probe.h | 9 ++
6 files changed, 248 insertions(+), 29 deletions(-)

diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig
index 8e10a9453c96..b3f90d602896 100644
--- a/kernel/trace/Kconfig
+++ b/kernel/trace/Kconfig
@@ -664,6 +664,18 @@ config FPROBE_EVENTS
and the kprobe events on function entry and exit will be
transparently converted to this fprobe events.

+config PROBE_EVENTS_BTF_ARGS
+ depends on HAVE_FUNCTION_ARG_ACCESS_API
+ depends on FPROBE_EVENTS || KPROBE_EVENTS
+ depends on DEBUG_INFO_BTF && BPF_SYSCALL
+ bool "Support BTF function arguments for probe events"
+ default y
+ help
+ The user can specify the arguments of the probe event using the names
+ of the arguments of the probed function, when the probe location is a
+ kernel function entry or a tracepoint.
+ This is available only if BTF (BPF Type Format) support is enabled.
+
config KPROBE_EVENTS
depends on KPROBES
depends on HAVE_REGS_AND_STACK_ACCESS_API
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index abcc2ca615e8..7bd2741356ef 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -5670,7 +5670,11 @@ static const char readme_msg[] =
"\t args: <name>=fetcharg[:type]\n"
"\t fetcharg: (%<register>|$<efield>), @ , @<symbol>[+|-<offset>],\n"
#ifdef CONFIG_HAVE_FUNCTION_ARG_ACCESS_API
+#ifdef CONFIG_PROBE_EVENTS_BTF_ARGS
+ "\t $stack<index>, $stack, $retval, $comm, $arg<N>, <argname>\n"
+#else
"\t $stack<index>, $stack, $retval, $comm, $arg<N>,\n"
+#endif
#else
"\t $stack<index>, $stack, $retval, $comm,\n"
#endif
diff --git a/kernel/trace/trace_fprobe.c b/kernel/trace/trace_fprobe.c
index 2eb52bc602b8..f6e6c34174b6 100644
--- a/kernel/trace/trace_fprobe.c
+++ b/kernel/trace/trace_fprobe.c
@@ -367,6 +367,7 @@ static void free_trace_fprobe(struct trace_fprobe *tf)
static struct trace_fprobe *alloc_trace_fprobe(const char *group,
const char *event,
const char *symbol,
+ struct tracepoint *tpoint,
int maxactive,
int nargs, bool is_return)
{
@@ -386,6 +387,7 @@ static struct trace_fprobe *alloc_trace_fprobe(const char *group,
else
tf->fp.entry_handler = fentry_dispatcher;

+ tf->tpoint = tpoint;
tf->fp.nr_maxactive = maxactive;

ret = trace_probe_init(&tf->tp, event, group, false);
@@ -931,8 +933,12 @@ static int __trace_fprobe_create(int argc, const char *argv[])
int maxactive = 0;
char buf[MAX_EVENT_NAME_LEN];
char gbuf[MAX_EVENT_NAME_LEN];
- unsigned int flags = TPARG_FL_KERNEL;
+ char sbuf[KSYM_NAME_LEN];
bool is_tracepoint = false;
+ struct tracepoint *tpoint = NULL;
+ struct traceprobe_parse_context ctx = {
+ .flags = TPARG_FL_KERNEL | TPARG_FL_FENTRY,
+ };

if ((argv[0][0] != 'f' && argv[0][0] != 't') || argc < 2)
return -ECANCELED;
@@ -996,12 +1002,6 @@ static int __trace_fprobe_create(int argc, const char *argv[])
goto parse_error;
}

- flags |= TPARG_FL_FENTRY;
- if (is_return)
- flags |= TPARG_FL_RETURN;
- if (is_tracepoint)
- flags |= TPARG_FL_TPOINT;
-
trace_probe_log_set_index(0);
if (event) {
ret = traceprobe_parse_event_name(&event, &group, gbuf,
@@ -1013,7 +1013,8 @@ static int __trace_fprobe_create(int argc, const char *argv[])
if (!event) {
/* Make a new event name */
if (is_tracepoint)
- strscpy(buf, symbol, MAX_EVENT_NAME_LEN);
+ snprintf(buf, MAX_EVENT_NAME_LEN, "%s%s",
+ isdigit(*symbol) ? "_" : "", symbol);
else
snprintf(buf, MAX_EVENT_NAME_LEN, "%s__%s", symbol,
is_return ? "exit" : "entry");
@@ -1021,8 +1022,25 @@ static int __trace_fprobe_create(int argc, const char *argv[])
event = buf;
}

+ if (is_return)
+ ctx.flags |= TPARG_FL_RETURN;
+
+ if (is_tracepoint) {
+ ctx.flags |= TPARG_FL_TPOINT;
+ tpoint = find_tracepoint(symbol);
+ if (!tpoint) {
+ trace_probe_log_set_index(1);
+ trace_probe_log_err(0, NO_TRACEPOINT);
+ goto parse_error;
+ }
+ ctx.funcname = kallsyms_lookup(
+ (unsigned long)tpoint->probestub,
+ NULL, NULL, NULL, sbuf);
+ } else
+ ctx.funcname = symbol;
+
/* setup a probe */
- tf = alloc_trace_fprobe(group, event, symbol, maxactive,
+ tf = alloc_trace_fprobe(group, event, symbol, tpoint, maxactive,
argc - 2, is_return);
if (IS_ERR(tf)) {
ret = PTR_ERR(tf);
@@ -1031,24 +1049,15 @@ static int __trace_fprobe_create(int argc, const char *argv[])
goto out; /* We know tf is not allocated */
}

- if (is_tracepoint) {
- tf->tpoint = find_tracepoint(tf->symbol);
- if (!tf->tpoint) {
- trace_probe_log_set_index(1);
- trace_probe_log_err(0, NO_TRACEPOINT);
- goto parse_error;
- }
+ if (is_tracepoint)
tf->mod = __module_text_address(
(unsigned long)tf->tpoint->probestub);
- }

argc -= 2; argv += 2;
-
/* parse arguments */
for (i = 0; i < argc && i < MAX_TRACE_ARGS; i++) {
- struct traceprobe_parse_context ctx = { .flags = flags };
-
trace_probe_log_set_index(i + 2);
+ ctx.offset = 0;
ret = traceprobe_parse_probe_arg(&tf->tp, i, argv[i], &ctx);
if (ret)
goto error; /* This can be -ENOMEM */
diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
index fd62de2a2f51..aff6c1a5e161 100644
--- a/kernel/trace/trace_kprobe.c
+++ b/kernel/trace/trace_kprobe.c
@@ -742,7 +742,7 @@ static int __trace_kprobe_create(int argc, const char *argv[])
void *addr = NULL;
char buf[MAX_EVENT_NAME_LEN];
char gbuf[MAX_EVENT_NAME_LEN];
- unsigned int flags = TPARG_FL_KERNEL;
+ struct traceprobe_parse_context ctx = { .flags = TPARG_FL_KERNEL };

switch (argv[0][0]) {
case 'r':
@@ -823,10 +823,10 @@ static int __trace_kprobe_create(int argc, const char *argv[])
goto parse_error;
}
if (is_return)
- flags |= TPARG_FL_RETURN;
+ ctx.flags |= TPARG_FL_RETURN;
ret = kprobe_on_func_entry(NULL, symbol, offset);
if (ret == 0)
- flags |= TPARG_FL_FENTRY;
+ ctx.flags |= TPARG_FL_FENTRY;
/* Defer the ENOENT case until register kprobe */
if (ret == -EINVAL && is_return) {
trace_probe_log_err(0, BAD_RETPROBE);
@@ -856,7 +856,7 @@ static int __trace_kprobe_create(int argc, const char *argv[])

/* setup a probe */
tk = alloc_trace_kprobe(group, event, addr, symbol, offset, maxactive,
- argc - 2, is_return);
+ argc - 2, is_return);
if (IS_ERR(tk)) {
ret = PTR_ERR(tk);
/* This must return -ENOMEM, else there is a bug */
@@ -866,10 +866,10 @@ static int __trace_kprobe_create(int argc, const char *argv[])
argc -= 2; argv += 2;

/* parse arguments */
+ ctx.funcname = symbol;
for (i = 0; i < argc && i < MAX_TRACE_ARGS; i++) {
- struct traceprobe_parse_context ctx = { .flags = flags };
-
trace_probe_log_set_index(i + 2);
+ ctx.offset = 0;
ret = traceprobe_parse_probe_arg(&tk->tp, i, argv[i], &ctx);
if (ret)
goto error; /* This can be -ENOMEM */
diff --git a/kernel/trace/trace_probe.c b/kernel/trace/trace_probe.c
index 84a9f0446390..346673e9dfd4 100644
--- a/kernel/trace/trace_probe.c
+++ b/kernel/trace/trace_probe.c
@@ -11,6 +11,8 @@
*/
#define pr_fmt(fmt) "trace_probe: " fmt

+#include <linux/bpf.h>
+
#include "trace_probe.h"

#undef C
@@ -300,6 +302,171 @@ static int parse_trace_event_arg(char *arg, struct fetch_insn *code,
return -ENOENT;
}

+#ifdef CONFIG_PROBE_EVENTS_BTF_ARGS
+
+static struct btf *traceprobe_get_btf(void)
+{
+ struct btf *btf = bpf_get_btf_vmlinux();
+
+ if (IS_ERR_OR_NULL(btf))
+ return NULL;
+
+ return btf;
+}
+
+static u32 btf_type_int(const struct btf_type *t)
+{
+ return *(u32 *)(t + 1);
+}
+
+static const char *type_from_btf_id(struct btf *btf, s32 id)
+{
+ const struct btf_type *t;
+ u32 intdata;
+ s32 tid;
+
+ /* TODO: const char * could be converted as a string */
+ t = btf_type_skip_modifiers(btf, id, &tid);
+
+ switch (BTF_INFO_KIND(t->info)) {
+ case BTF_KIND_ENUM:
+ /* enum is "int", so convert to "s32" */
+ return "s32";
+ case BTF_KIND_ENUM64:
+ return "s64";
+ case BTF_KIND_PTR:
+ /* pointer will be converted to "x??" */
+ if (IS_ENABLED(CONFIG_64BIT))
+ return "x64";
+ else
+ return "x32";
+ case BTF_KIND_INT:
+ intdata = btf_type_int(t);
+ if (BTF_INT_ENCODING(intdata) & BTF_INT_SIGNED) {
+ switch (BTF_INT_BITS(intdata)) {
+ case 8:
+ return "s8";
+ case 16:
+ return "s16";
+ case 32:
+ return "s32";
+ case 64:
+ return "s64";
+ }
+ } else { /* unsigned */
+ switch (BTF_INT_BITS(intdata)) {
+ case 8:
+ return "u8";
+ case 16:
+ return "u16";
+ case 32:
+ return "u32";
+ case 64:
+ return "u64";
+ }
+ }
+ }
+ /* TODO: support other types */
+
+ return NULL;
+}
+
+static const struct btf_param *find_btf_func_param(const char *funcname, s32 *nr)
+{
+ struct btf *btf = traceprobe_get_btf();
+ const struct btf_type *t;
+ s32 id;
+
+ if (!btf || !funcname || !nr)
+ return ERR_PTR(-EINVAL);
+
+ id = btf_find_by_name_kind(btf, funcname, BTF_KIND_FUNC);
+ if (id <= 0)
+ return ERR_PTR(-ENOENT);
+
+ /* Get BTF_KIND_FUNC type */
+ t = btf_type_by_id(btf, id);
+ if (!btf_type_is_func(t))
+ return ERR_PTR(-ENOENT);
+
+ /* The type of BTF_KIND_FUNC is BTF_KIND_FUNC_PROTO */
+ t = btf_type_by_id(btf, t->type);
+ if (!btf_type_is_func_proto(t))
+ return ERR_PTR(-ENOENT);
+
+ *nr = btf_type_vlen(t);
+
+ if (*nr)
+ return (const struct btf_param *)(t + 1);
+ else
+ return NULL;
+}
+
+static int parse_btf_arg(const char *varname, struct fetch_insn *code,
+ struct traceprobe_parse_context *ctx)
+{
+ struct btf *btf = traceprobe_get_btf();
+ const struct btf_param *params;
+ int i;
+
+ if (!btf) {
+ trace_probe_log_err(ctx->offset, NOSUP_BTFARG);
+ return -EOPNOTSUPP;
+ }
+
+ if (WARN_ON_ONCE(!ctx->funcname))
+ return -EINVAL;
+
+ if (!ctx->params) {
+ params = find_btf_func_param(ctx->funcname, &ctx->nr_params);
+ if (IS_ERR(params)) {
+ trace_probe_log_err(ctx->offset, NO_BTF_ENTRY);
+ return PTR_ERR(params);
+ }
+ ctx->params = params;
+ } else
+ params = ctx->params;
+
+ for (i = 0; i < ctx->nr_params; i++) {
+ const char *name = btf_name_by_offset(btf, params[i].name_off);
+
+ if (name && !strcmp(name, varname)) {
+ code->op = FETCH_OP_ARG;
+ code->param = i;
+ return 0;
+ }
+ }
+ trace_probe_log_err(ctx->offset, NO_BTFARG);
+ return -ENOENT;
+}
+
+static const struct fetch_type *parse_btf_arg_type(int arg_idx,
+ struct traceprobe_parse_context *ctx)
+{
+ struct btf *btf = traceprobe_get_btf();
+ const char *typestr = NULL;
+
+ if (btf && ctx->params)
+ typestr = type_from_btf_id(btf, ctx->params[arg_idx].type);
+
+ return find_fetch_type(typestr, ctx->flags);
+}
+#else
+static struct btf *traceprobe_get_btf(void)
+{
+ return NULL;
+}
+
+static int parse_btf_arg(const char *varname, struct fetch_insn *code,
+ struct traceprobe_parse_context *ctx)
+{
+ trace_probe_log_err(ctx->offset, NOSUP_BTFARG);
+ return -EOPNOTSUPP;
+}
+#define parse_btf_arg_type(idx, ctx) \
+ find_fetch_type(NULL, ctx->flags)
+#endif
+
#define PARAM_MAX_STACK (THREAD_SIZE / sizeof(unsigned long))

static int parse_probe_vars(char *arg, const struct fetch_type *t,
@@ -556,6 +723,15 @@ parse_probe_arg(char *arg, const struct fetch_type *type,
code->op = FETCH_OP_IMM;
}
break;
+ default:
+ if (isalpha(arg[0]) || arg[0] == '_') { /* BTF variable */
+ if (!tparg_is_function_entry(ctx->flags)) {
+ trace_probe_log_err(ctx->offset, NOSUP_BTFARG);
+ return -EINVAL;
+ }
+ ret = parse_btf_arg(arg, code, ctx);
+ break;
+ }
}
if (!ret && code->op == FETCH_OP_NOP) {
/* Parsed, but do not find fetch method */
@@ -704,6 +880,11 @@ static int traceprobe_parse_probe_arg_body(const char *argv, ssize_t *size,
if (ret)
goto fail;

+ /* Update storing type if BTF is available */
+ if (IS_ENABLED(CONFIG_PROBE_EVENTS_BTF_ARGS) &&
+ !t && code->op == FETCH_OP_ARG)
+ parg->type = parse_btf_arg_type(code->param, ctx);
+
ret = -EINVAL;
/* Store operation */
if (parg->type->is_string) {
@@ -857,8 +1038,14 @@ int traceprobe_parse_probe_arg(struct trace_probe *tp, int i, const char *arg,
parg->name = kmemdup_nul(arg, body - arg, GFP_KERNEL);
body++;
} else {
- /* If argument name is omitted, set "argN" */
- parg->name = kasprintf(GFP_KERNEL, "arg%d", i + 1);
+ /*
+ * If argument name is omitted, try arg as a name (BTF variable)
+ * or "argN".
+ */
+ if (is_good_name(arg))
+ parg->name = kstrdup(arg, GFP_KERNEL);
+ else
+ parg->name = kasprintf(GFP_KERNEL, "arg%d", i + 1);
body = arg;
}
if (!parg->name)
diff --git a/kernel/trace/trace_probe.h b/kernel/trace/trace_probe.h
index 2dc1e5c4c9e8..9ea5c7e8753f 100644
--- a/kernel/trace/trace_probe.h
+++ b/kernel/trace/trace_probe.h
@@ -23,6 +23,7 @@
#include <linux/limits.h>
#include <linux/uaccess.h>
#include <linux/bitops.h>
+#include <linux/btf.h>
#include <asm/bitsperlong.h>

#include "trace.h"
@@ -376,6 +377,9 @@ static inline bool tparg_is_function_entry(unsigned int flags)

struct traceprobe_parse_context {
struct trace_event_call *event;
+ const struct btf_param *params;
+ s32 nr_params;
+ const char *funcname;
unsigned int flags;
int offset;
};
@@ -474,7 +478,10 @@ extern int traceprobe_define_arg_fields(struct trace_event_call *event_call,
C(NO_EVENT_INFO, "This requires both group and event name to attach"),\
C(BAD_ATTACH_EVENT, "Attached event does not exist"),\
C(BAD_ATTACH_ARG, "Attached event does not have this field"),\
- C(NO_EP_FILTER, "No filter rule after 'if'"),
+ C(NO_EP_FILTER, "No filter rule after 'if'"), \
+ C(NOSUP_BTFARG, "BTF is not available or not supported"), \
+ C(NO_BTFARG, "This variable is not found at this probe point"),\
+ C(NO_BTF_ENTRY, "No BTF entry for this probe point"),

#undef C
#define C(a, b) TP_ERR_##a