[PATCH v3 2/9] bpf/btf: tracing: Move finding func-proto API and getting func-param API to BTF

Masami Hiramatsu (Google)
2023-07-26T13:00:29Z

Move generic function-proto find API and getting function parameter API
to BTF library code from trace_probe.c. This will avoid redundant efforts
on different feature.

Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
---
Changes in v3:
- Remove perameter check.
- Fix a typo.
- Add a type check for btf_get_func_param() and add comment for that.
- Use bpf_find_btf_id() and add bpf_put().
- Move the code before btf_show() related code.
---
include/linux/btf.h | 4 ++++
kernel/bpf/btf.c | 47 +++++++++++++++++++++++++++++++++++++++++
kernel/trace/trace_probe.c | 50 +++++++++-----------------------------------
3 files changed, 61 insertions(+), 40 deletions(-)

diff --git a/include/linux/btf.h b/include/linux/btf.h
index dbfe41a09c4b..20e3a07eef8f 100644
--- a/include/linux/btf.h
+++ b/include/linux/btf.h
@@ -222,6 +222,10 @@ const struct btf_type *
btf_resolve_size(const struct btf *btf, const struct btf_type *type,
u32 *type_size);
const char *btf_type_str(const struct btf_type *t);
+const struct btf_type *btf_find_func_proto(const char *func_name,
+ struct btf **btf_p);
+const struct btf_param *btf_get_func_param(const struct btf_type *func_proto,
+ s32 *nr);

#define for_each_member(i, struct_type, member) \
for (i = 0, member = btf_type_member(struct_type); \
diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index b9b0eb1189bb..f7b25c615269 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -911,6 +911,53 @@ static const struct btf_type *btf_type_skip_qualifiers(const struct btf *btf,
return t;
}

+/*
+ * Find a function proto type by name, and return the btf_type with its btf
+ * in *@btf_p. Return NULL if not found.
+ * Note that caller has to call btf_put(*@btf_p) after using the btf_type.
+ */
+const struct btf_type *btf_find_func_proto(const char *func_name, struct btf **btf_p)
+{
+ const struct btf_type *t;
+ s32 id;
+
+ id = bpf_find_btf_id(func_name, BTF_KIND_FUNC, btf_p);
+ if (id < 0)
+ return NULL;
+
+ /* Get BTF_KIND_FUNC type */
+ t = btf_type_by_id(*btf_p, id);
+ if (!t || !btf_type_is_func(t))
+ goto err;
+
+ /* The type of BTF_KIND_FUNC is BTF_KIND_FUNC_PROTO */
+ t = btf_type_by_id(*btf_p, t->type);
+ if (!t || !btf_type_is_func_proto(t))
+ goto err;
+
+ return t;
+err:
+ btf_put(*btf_p);
+ return NULL;
+}
+
+/*
+ * Get function parameter with the number of parameters.
+ * This can return NULL if the function has no parameters.
+ * It can return -EINVAL if the @func_proto is not a function proto type.
+ */
+const struct btf_param *btf_get_func_param(const struct btf_type *func_proto, s32 *nr)
+{
+ if (!btf_type_is_func_proto(func_proto))
+ return ERR_PTR(-EINVAL);
+
+ *nr = btf_type_vlen(func_proto);
+ if (*nr > 0)
+ return (const struct btf_param *)(func_proto + 1);
+ else
+ return NULL;
+}
+
#define BTF_SHOW_MAX_ITER 10

#define BTF_KIND_BIT(kind) (1ULL << kind)
diff --git a/kernel/trace/trace_probe.c b/kernel/trace/trace_probe.c
index ecbe28f8d676..21a228d88ebb 100644
--- a/kernel/trace/trace_probe.c
+++ b/kernel/trace/trace_probe.c
@@ -361,38 +361,6 @@ static const char *type_from_btf_id(struct btf *btf, s32 id)
return NULL;
}

-static const struct btf_type *find_btf_func_proto(const char *funcname,
- struct btf **btf_p)
-{
- const struct btf_type *t;
- struct btf *btf = NULL;
- s32 id;
-
- if (!funcname)
- return ERR_PTR(-EINVAL);
-
- id = bpf_find_btf_id(funcname, BTF_KIND_FUNC, &btf);
- if (id <= 0)
- return ERR_PTR(-ENOENT);
-
- /* Get BTF_KIND_FUNC type */
- t = btf_type_by_id(btf, id);
- if (!t || !btf_type_is_func(t))
- goto err;
-
- /* The type of BTF_KIND_FUNC is BTF_KIND_FUNC_PROTO */
- t = btf_type_by_id(btf, t->type);
- if (!t || !btf_type_is_func_proto(t))
- goto err;
-
- *btf_p = btf;
- return t;
-
-err:
- btf_put(btf);
- return ERR_PTR(-ENOENT);
-}
-
static const struct btf_param *find_btf_func_param(const char *funcname, s32 *nr,
struct btf **btf_p, bool tracepoint)
{
@@ -403,12 +371,13 @@ static const struct btf_param *find_btf_func_param(const char *funcname, s32 *nr
if (!funcname || !nr)
return ERR_PTR(-EINVAL);

- t = find_btf_func_proto(funcname, &btf);
- if (IS_ERR(t))
+ t = btf_find_func_proto(funcname, &btf);
+ if (!t)
return (const struct btf_param *)t;

- *nr = btf_type_vlen(t);
- param = (const struct btf_param *)(t + 1);
+ param = btf_get_func_param(t, nr);
+ if (IS_ERR_OR_NULL(param))
+ goto err;

/* Hide the first 'data' argument of tracepoint */
if (tracepoint) {
@@ -421,6 +390,7 @@ static const struct btf_param *find_btf_func_param(const char *funcname, s32 *nr
return param;
}

+err:
btf_put(btf);
return NULL;
}
@@ -496,8 +466,8 @@ static const struct fetch_type *parse_btf_retval_type(

if (ctx->funcname) {
/* Do not use ctx->btf, because it must be used with ctx->param */
- t = find_btf_func_proto(ctx->funcname, &btf);
- if (!IS_ERR(t)) {
+ t = btf_find_func_proto(ctx->funcname, &btf);
+ if (t) {
typestr = type_from_btf_id(btf, t->type);
btf_put(btf);
}
@@ -512,8 +482,8 @@ static bool is_btf_retval_void(const char *funcname)
struct btf *btf;
bool ret;

- t = find_btf_func_proto(funcname, &btf);
- if (IS_ERR(t))
+ t = btf_find_func_proto(funcname, &btf);
+ if (!t)
return false;

ret = (t->type == 0);