Messages in this thread | ![/](/images/icornerl.gif) | | Date | Mon, 23 May 2022 19:08:54 -0400 | From | Michael Mullin <> | Subject | Re: [PATCH] bpftool: mmaped fields missing map structure in generated skeletons |
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On Mon, May 23, 2022 at 03:38:03PM -0700, Andrii Nakryiko wrote: > On Mon, May 23, 2022 at 3:19 PM Michael Mullin <masmullin@gmail.com> wrote: > > > > On Mon, May 23, 2022 at 03:02:31PM -0700, Andrii Nakryiko wrote: > > > On Mon, May 23, 2022 at 1:26 PM Michael Mullin <masmullin@gmail.com> wrote: > > > > > > > > When generating a skeleton which has an mmaped map field, bpftool's > > > > output is missing the map structure. This causes a compile break when > > > > the generated skeleton is compiled as the field belongs to the internal > > > > struct maps, not directly to the obj. > > > > > > > > Signed-off-by: Michael Mullin <masmullin@gmail.com> > > > > --- > > > > tools/bpf/bpftool/gen.c | 2 +- > > > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > > > > > diff --git a/tools/bpf/bpftool/gen.c b/tools/bpf/bpftool/gen.c > > > > index f158dc1c2149..b49293795ba0 100644 > > > > --- a/tools/bpf/bpftool/gen.c > > > > +++ b/tools/bpf/bpftool/gen.c > > > > @@ -853,7 +853,7 @@ codegen_maps_skeleton(struct bpf_object *obj, size_t map_cnt, bool mmaped) > > > > i, bpf_map__name(map), i, ident); > > > > /* memory-mapped internal maps */ > > > > if (mmaped && is_internal_mmapable_map(map, ident, sizeof(ident))) { > > > > - printf("\ts->maps[%zu].mmaped = (void **)&obj->%s;\n", > > > > + printf("\ts->maps[%zu].mmaped = (void **)&obj->maps.%s;\n", > > > > > > That's not right. maps.my_map is struct bpf_map *, but mmaped is > > > supposed to be a blob of memory that is memory-mapped into map. > > > > > > Can you elaborate on how you trigger that compilation error with a > > > small example? > > > > I have an a very small example on github. I have added some sed fixes to > > my Makefile make my sample program compile. > > https://github.com/masmullin2000/libbpf-sample/tree/main/c/simple > > > > https://github.com/masmullin2000/libbpf-sample/tree/02c7f945bf9027daedec04f485a320ba2df28204/c/simple > > contains broken code. > > You are missing -g when calling clang to generate debug info (DWARF > and subsequently BTF). When BPF object file doesn't have BTF, we don't > generate those bss/data/rodata/etc sections of the skeleton. You > should be good just by adding -g. >
Thank you. By using -g, I am also unable to trigger the segfault I was trying to fix with the patch https://lore.kernel.org/bpf/20220523194917.igkgorco42537arb@jup/T/#u
I am not sure if there would be other ways to trigger the segfault.
> > > > I apologize if this is an incorrect way to share external code. I > > haven't found the proper way to share example code from > > kernelnewbies.org > > > > > > > > > i, ident); > > > > } > > > > i++; > > > > -- > > > > 2.36.1 > > > >
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