Re: [PATCH v2 2/9] bpf/btf: tracing: Move finding func-proto API and getting func-param API to BTF

[Masami Hiramatsu (Google) <mhiramat@kernel.org>]

On Tue, 18 Jul 2023 10:40:09 +0800
Donglin Peng <dolinux.peng@gmail.com> wrote:

> On Mon, Jul 17, 2023 at 11:24 PM Masami Hiramatsu (Google)
> <mhiramat@kernel.org> wrote:
> >
> > From: Masami Hiramatsu (Google) <mhiramat@kernel.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@kernel.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);
> > +       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();
> 
> I found that traceprobe_get_btf() only returns the vmlinux's btf. But
> if the function is
> defined in a kernel module, we should get the module's btf.
> 

Good catch! That should be a separated fix (or improvement?)
I think it's better to use btf_get() and btf_put(), and pass btf via
traceprobe_parse_context.

Thank you! 

> -- Donglin
> 
> >         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;
> >
> >


-- 
Masami Hiramatsu (Google) <mhiramat@kernel.org>