On Wed, 19 Jul 2023 13:36:48 +0100
Alan Maguire <alan.maguire@xxxxxxxxxx> wrote:
> On 17/07/2023 16:23, Masami Hiramatsu (Google) wrote:
> > From: Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>
> >
> > 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@xxxxxxxxxx>
> > ---
> > 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
That's a good point! I'm checking fprobe, but kprobes actually
uses those suffixed names.
>
> $ echo 'f schedule_work.isra.0 $arg*' >> dynamic_events
> bash: echo: write error: No such file or directory
So maybe fprobe doesn't accept that.
> 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!
OK, that's not a problem. My concern is that some "constprop" functions
will replace a part of parameter with constant value (so it can skip
passing some arguments). BTF argument may not work in such case.
Let me check it.
Thank you,
>
> 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;
> >
> >
--
Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>
