On Mon, Jan 06, 2020 at 09:36:17PM +0000, Yonghong Song wrote:
>
>
> On 12/29/19 6:37 AM, Jiri Olsa wrote:
> > I'm not sure why the restriction was added,
> > but I can't access pointers to POD types like
> > const char * when probing vfs_read function.
> >
> > Removing the check and allow non struct type
> > access in context.
> >
> > Signed-off-by: Jiri Olsa <jolsa@xxxxxxxxxx>
> > ---
> > kernel/bpf/btf.c | 6 ------
> > 1 file changed, 6 deletions(-)
> >
> > diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
> > index ed2075884724..ae90f60ac1b8 100644
> > --- a/kernel/bpf/btf.c
> > +++ b/kernel/bpf/btf.c
> > @@ -3712,12 +3712,6 @@ bool btf_ctx_access(int off, int size, enum bpf_access_type type,
> > /* skip modifiers */
> > while (btf_type_is_modifier(t))
> > t = btf_type_by_id(btf, t->type);
> > - if (!btf_type_is_struct(t)) {
> > - bpf_log(log,
> > - "func '%s' arg%d type %s is not a struct\n",
> > - tname, arg, btf_kind_str[BTF_INFO_KIND(t->info)]);
> > - return false;
> > - }
>
> Hi, Jiri, the RFC looks great! Especially, you also referenced this will
> give great performance boost for bcc scripts.
>
> Could you provide more context on why the above change is needed?
> The function btf_ctx_access is used to check validity of accessing
> function parameters which are wrapped inside a structure, I am wondering
> what kinds of accesses you tried to address here.
when I was transforming opensnoop.py to use this I got fail in
there when I tried to access filename arg in do_sys_open
but actualy it seems this should get recognized earlier by:
if (btf_type_is_int(t))
/* accessing a scalar */
return true;
I'm not sure why it did not pass for const char*, I'll check
jirka
