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Message-ID: <13926373-1beb-16f4-180e-f529a8c9b0a7@oracle.com>
Date: Wed, 19 Jul 2023 13:36:48 +0100
From: Alan Maguire <alan.maguire@...cle.com>
To: "Masami Hiramatsu (Google)" <mhiramat@...nel.org>,
linux-trace-kernel@...r.kernel.org
Cc: linux-kernel@...r.kernel.org, Steven Rostedt <rostedt@...dmis.org>,
Martin KaFai Lau <martin.lau@...ux.dev>, bpf@...r.kernel.org,
Sven Schnelle <svens@...ux.ibm.com>,
Alexei Starovoitov <ast@...nel.org>
Subject: Re: [PATCH v2 2/9] bpf/btf: tracing: Move finding func-proto API and
getting func-param API to BTF
On 17/07/2023 16:23, Masami Hiramatsu (Google) wrote:
> From: Masami Hiramatsu (Google) <mhiramat@...nel.org>
>
> 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@...nel.org>
> ---
> include/linux/btf.h | 4 ++++
> kernel/bpf/btf.c | 45 ++++++++++++++++++++++++++++++++++++++++
> kernel/trace/trace_probe.c | 50 +++++++++++++-------------------------------
> 3 files changed, 64 insertions(+), 35 deletions(-)
>
> diff --git a/include/linux/btf.h b/include/linux/btf.h
> index cac9f304e27a..98fbbcdd72ec 100644
> --- a/include/linux/btf.h
> +++ b/include/linux/btf.h
> @@ -221,6 +221,10 @@ 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(struct btf *btf,
> + const char *func_name);
> +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 817204d53372..e015b52956cb 100644
> --- a/kernel/bpf/btf.c
> +++ b/kernel/bpf/btf.c
> @@ -1947,6 +1947,51 @@ btf_resolve_size(const struct btf *btf, const struct btf_type *type,
> return __btf_resolve_size(btf, type, type_size, NULL, NULL, NULL, NULL);
> }
>
> +/*
> + * Find a functio proto type by name, and return it.
> + * Return NULL if not found, or return -EINVAL if parameter is invalid.
> + */
> +const struct btf_type *btf_find_func_proto(struct btf *btf, const char *func_name)
> +{
> + const struct btf_type *t;
> + s32 id;
> +
> + if (!btf || !func_name)
> + return ERR_PTR(-EINVAL);
> +
> + id = btf_find_by_name_kind(btf, func_name, BTF_KIND_FUNC);
as mentioned in my other mail, there are cases where the function name
may have a .isra.0 suffix, but the BTF representation will not. I looked
at this and it seems like symbol names are validated via
traceprobe_parse_event_name() - will this validation allow a "."-suffix
name? I tried the following (with pahole v1.25 that emits BTF for
schedule_work.isra.0):
[45454] FUNC 'schedule_work' type_id=45453 linkage=static
$ echo 'f schedule_work.isra.0 $arg*' >> dynamic_events
bash: echo: write error: No such file or directory
So presuming that such "."-suffixed names are allowed, would it make
sense to fall back to search BTF for the prefix ("schedule_work")
instead of the full name ("schedule_work.isra.0"), as the former is what
makes it into the BTF representation? Thanks!
Alan
> + if (id <= 0)
> + return NULL;
> +
> + /* Get BTF_KIND_FUNC type */
> + t = btf_type_by_id(btf, id);
> + if (!t || !btf_type_is_func(t))
> + return NULL;
> +
> + /* 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))
> + return NULL;
> +
> + return t;
> +}
> +
> +/*
> + * Get function parameter with the number of parameters.
> + * This can return NULL if the function has no parameters.
> + */
> +const struct btf_param *btf_get_func_param(const struct btf_type *func_proto, s32 *nr)
> +{
> + if (!func_proto || !nr)
> + return ERR_PTR(-EINVAL);
> +
> + *nr = btf_type_vlen(func_proto);
> + if (*nr > 0)
> + return (const struct btf_param *)(func_proto + 1);
> + else
> + return NULL;
> +}
> +
> static u32 btf_resolved_type_id(const struct btf *btf, u32 type_id)
> {
> while (type_id < btf->start_id)
> diff --git a/kernel/trace/trace_probe.c b/kernel/trace/trace_probe.c
> index c68a72707852..cd89fc1ebb42 100644
> --- a/kernel/trace/trace_probe.c
> +++ b/kernel/trace/trace_probe.c
> @@ -371,47 +371,23 @@ 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 = traceprobe_get_btf();
> - const struct btf_type *t;
> - s32 id;
> -
> - if (!btf || !funcname)
> - 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 (!t || !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 (!t || !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,
> bool tracepoint)
> {
> + struct btf *btf = traceprobe_get_btf();
> const struct btf_param *param;
> const struct btf_type *t;
>
> - if (!funcname || !nr)
> + if (!funcname || !nr || !btf)
> return ERR_PTR(-EINVAL);
>
> - t = find_btf_func_proto(funcname);
> - if (IS_ERR(t))
> + t = btf_find_func_proto(btf, funcname);
> + if (IS_ERR_OR_NULL(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))
> + return param;
>
> /* Hide the first 'data' argument of tracepoint */
> if (tracepoint) {
> @@ -490,8 +466,8 @@ static const struct fetch_type *parse_btf_retval_type(
> const struct btf_type *t;
>
> if (btf && ctx->funcname) {
> - t = find_btf_func_proto(ctx->funcname);
> - if (!IS_ERR(t))
> + t = btf_find_func_proto(btf, ctx->funcname);
> + if (!IS_ERR_OR_NULL(t))
> typestr = type_from_btf_id(btf, t->type);
> }
>
> @@ -500,10 +476,14 @@ static const struct fetch_type *parse_btf_retval_type(
>
> static bool is_btf_retval_void(const char *funcname)
> {
> + struct btf *btf = traceprobe_get_btf();
> const struct btf_type *t;
>
> - t = find_btf_func_proto(funcname);
> - if (IS_ERR(t))
> + if (!btf)
> + return false;
> +
> + t = btf_find_func_proto(btf, funcname);
> + if (IS_ERR_OR_NULL(t))
> return false;
>
> return t->type == 0;
>
>
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