[PATCH v9.1 08/11] tracing/probes: Add BTF retval type support

Masami Hiramatsu (Google)
2023-05-02T02:19:27Z

Check the target function has non-void retval type and set the correct
fetch type if user doesn't specify it.
If the function returns void, $retval is rejected as below;

# echo 'f unregister_kprobes%return $retval' >> dynamic_events
sh: write error: No such file or directory
# cat error_log
[ 37.488397] trace_fprobe: error: This function returns 'void' type
Command: f unregister_kprobes%return $retval
^

Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
---
Changes in v8:
- Fix wrong indentation.
Changes in v7:
- Introduce this as a new patch.
---
kernel/trace/trace_probe.c | 67 ++++++++++++++++++++++++++++++++++++++++----
kernel/trace/trace_probe.h | 1 +
2 files changed, 62 insertions(+), 6 deletions(-)

diff --git a/kernel/trace/trace_probe.c b/kernel/trace/trace_probe.c
index 4c3c70862a9a..cf1f05c230e8 100644
--- a/kernel/trace/trace_probe.c
+++ b/kernel/trace/trace_probe.c
@@ -371,13 +371,13 @@ static const char *type_from_btf_id(struct btf *btf, s32 id)
return NULL;
}

-static const struct btf_param *find_btf_func_param(const char *funcname, s32 *nr)
+static const struct btf_type *find_btf_func_proto(const char *funcname)
{
struct btf *btf = traceprobe_get_btf();
const struct btf_type *t;
s32 id;

- if (!btf || !funcname || !nr)
+ if (!btf || !funcname)
return ERR_PTR(-EINVAL);

id = btf_find_by_name_kind(btf, funcname, BTF_KIND_FUNC);
@@ -394,6 +394,20 @@ static const struct btf_param *find_btf_func_param(const char *funcname, s32 *nr
if (!btf_type_is_func_proto(t))
return ERR_PTR(-ENOENT);

+ return t;
+}
+
+static const struct btf_param *find_btf_func_param(const char *funcname, s32 *nr)
+{
+ const struct btf_type *t;
+
+ if (!funcname || !nr)
+ return ERR_PTR(-EINVAL);
+
+ t = find_btf_func_proto(funcname);
+ if (IS_ERR(t))
+ return (const struct btf_param *)t;
+
*nr = btf_type_vlen(t);

if (*nr)
@@ -452,6 +466,32 @@ static const struct fetch_type *parse_btf_arg_type(int arg_idx,
return find_fetch_type(typestr, ctx->flags);
}

+static const struct fetch_type *parse_btf_retval_type(
+ struct traceprobe_parse_context *ctx)
+{
+ struct btf *btf = traceprobe_get_btf();
+ const char *typestr = NULL;
+ const struct btf_type *t;
+
+ if (btf && ctx->funcname) {
+ t = find_btf_func_proto(ctx->funcname);
+ if (!IS_ERR(t))
+ typestr = type_from_btf_id(btf, t->type);
+ }
+
+ return find_fetch_type(typestr, ctx->flags);
+}
+
+static bool is_btf_retval_void(const char *funcname)
+{
+ const struct btf_type *t;
+
+ t = find_btf_func_proto(funcname);
+ if (IS_ERR(t))
+ return false;
+
+ return t->type == 0;
+}
#else
static struct btf *traceprobe_get_btf(void)
{
@@ -469,8 +509,15 @@ static int parse_btf_arg(const char *varname, struct fetch_insn *code,
trace_probe_log_err(ctx->offset, NOSUP_BTFARG);
return -EOPNOTSUPP;
}
+
#define parse_btf_arg_type(idx, ctx) \
find_fetch_type(NULL, ctx->flags)
+
+#define parse_btf_retval_type(ctx) \
+ find_fetch_type(NULL, ctx->flags)
+
+#define is_btf_retval_void(funcname) (false)
+
#endif

#define PARAM_MAX_STACK (THREAD_SIZE / sizeof(unsigned long))
@@ -500,7 +547,12 @@ static int parse_probe_vars(char *arg, const struct fetch_type *t,

if (strcmp(arg, "retval") == 0) {
if (ctx->flags & TPARG_FL_RETURN) {
- code->op = FETCH_OP_RETVAL;
+ if ((ctx->flags & TPARG_FL_KERNEL) &&
+ is_btf_retval_void(ctx->funcname)) {
+ trace_probe_log_err(ctx->offset, NO_RETVAL);
+ ret = -ENOENT;
+ } else
+ code->op = FETCH_OP_RETVAL;
} else {
trace_probe_log_err(ctx->offset, RETVAL_ON_PROBE);
ret = -EINVAL;
@@ -887,9 +939,12 @@ static int traceprobe_parse_probe_arg_body(const char *argv, ssize_t *size,
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);
+ if (IS_ENABLED(CONFIG_PROBE_EVENTS_BTF_ARGS) && !t) {
+ if (code->op == FETCH_OP_ARG)
+ parg->type = parse_btf_arg_type(code->param, ctx);
+ else if (code->op == FETCH_OP_RETVAL)
+ parg->type = parse_btf_retval_type(ctx);
+ }

ret = -EINVAL;
/* Store operation */
diff --git a/kernel/trace/trace_probe.h b/kernel/trace/trace_probe.h
index 8c5b029c5d62..3eb7c37c0984 100644
--- a/kernel/trace/trace_probe.h
+++ b/kernel/trace/trace_probe.h
@@ -444,6 +444,7 @@ extern int traceprobe_define_arg_fields(struct trace_event_call *event_call,
C(BAD_EVENT_NAME, "Event name must follow the same rules as C identifiers"), \
C(EVENT_EXIST, "Given group/event name is already used by another event"), \
C(RETVAL_ON_PROBE, "$retval is not available on probe"), \
+ C(NO_RETVAL, "This function returns 'void' type"), \
C(BAD_STACK_NUM, "Invalid stack number"), \
C(BAD_ARG_NUM, "Invalid argument number"), \
C(BAD_VAR, "Invalid $-valiable specified"), \