Re: [PATCH 2/2] btf_encoder: Change functions check due to broken dwarf

[Jiri Olsa <jolsa@redhat.com>]

On Mon, Nov 02, 2020 at 10:59:08PM +0100, Jiri Olsa wrote:
> On Sat, Oct 31, 2020 at 11:31:31PM +0100, Jiri Olsa wrote:
> > We need to generate just single BTF instance for the
> > function, while DWARF data contains multiple instances
> > of DW_TAG_subprogram tag.
> > 
> > Unfortunately we can no longer rely on DW_AT_declaration
> > tag (https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97060)
> > 
> > Instead we apply following checks:
> >   - argument names are defined for the function
> >   - there's symbol and address defined for the function
> >   - function is generated only once
> > 
> > Also because we want to follow kernel's ftrace traceable
> > functions, this patchset is adding extra check that the
> > function is one of the ftrace's functions.
> > 
> > All ftrace functions addresses are stored in vmlinux
> > binary within symbols:
> >   __start_mcount_loc
> >   __stop_mcount_loc
> 
> hum, for some reason this does not pass through bpf internal
> functions like bpf_iter_bpf_map.. I learned it hard way ;-)
> will check

so it gets filtered out because it's __init function
I'll check if the fix below catches all internal functions,
but I guess we should do something more robust

jirka


---
diff --git a/btf_encoder.c b/btf_encoder.c
index 0a378aa92142..3cd94280c35b 100644
--- a/btf_encoder.c
+++ b/btf_encoder.c
@@ -143,7 +143,8 @@ static int filter_functions(struct btf_elf *btfe, struct mcount_symbols *ms)
 		/* Do not enable .init section functions. */
 		if (init_filter &&
 		    func->addr >= ms->init_begin &&
-		    func->addr <  ms->init_end)
+		    func->addr <  ms->init_end &&
+		    strncmp("bpf_", func->name, 4))
 			continue;
 
 		/* Make sure function is within mcount addresses. */