Hi, I added Richard to the CC, who added the original BPF support. Who might remember where the R_BPF_MAP_FD comes from (see at the end).
On Fri, 2018-06-15 at 15:40 -0700, Yonghong Song wrote: > Due to libdw does not have proper BPF relocation support, > the pahole cannot display filenames correctly for objects > with default llvm options. So we have to invent > a special option "llc -march=bpf -mattr=dwarfris" to > prevent llvm from generating cross-section dwarf relocation > records (https://reviews.llvm.org/rL326505). > The pahole related discussion is in linux netdev > mailing list (http://lists.openwall.net/netdev/2018/06/15/38, etc.) > > We would like to add proper BPF relocation support > to libdw so eventually we could retire the special llc bpf > flag "-mattr=dwarfris". Yes. elfutils/libdwfl only does "simple relocations", but that is all you need anyway. Do you have a test file (binary for something simple/trivial generated by llc -march=bpf that contains at least one reloc). I looked at your implementation and I am sure it works correctly. But having a small testfile is always a plus. > The bpf relocations are defined in > llvm_repo:include/llvm/BinaryFormat/ELFRelocs/BPF.def: > ELF_RELOC(R_BPF_NONE, 0) > ELF_RELOC(R_BPF_64_64, 1) > ELF_RELOC(R_BPF_64_32, 10) > > Removed the relocation type R_BPF_MAP_FD whoes name does not > confirm to llvm definition and replaced it with R_BPF_64_64. > The BPF object is just a relocatible object, not an executable or > a shared library, so assign ELF type to REL only in bpf_reloc.def. > > Tested locally with building pahole with this patch and > pahole is able to display structures in bpf object file properly. Patch looks good. Thanks. I'll add a ChangeLog entry because that is what we still do. > Signed-off-by: Yonghong Song <y...@fb.com> > --- > backends/Makefile.am | 2 +- > backends/bpf_init.c | 1 + > backends/bpf_reloc.def | 3 ++- > backends/bpf_symbol.c | 54 > ++++++++++++++++++++++++++++++++++++++++++++++++++ > libelf/elf.h | 3 ++- > 5 files changed, 60 insertions(+), 3 deletions(-) > create mode 100644 backends/bpf_symbol.c > [...] > diff --git a/libelf/elf.h b/libelf/elf.h > index f7748983..940e88dd 100644 > --- a/libelf/elf.h > +++ b/libelf/elf.h > @@ -3848,7 +3848,8 @@ enum > /* BPF specific declarations. */ > > #define R_BPF_NONE 0 /* No reloc */ > -#define R_BPF_MAP_FD 1 /* Map fd to pointer */ > +#define R_BPF_64_64 1 > +#define R_BPF_64_32 10 We should sync this with glibc. This file really is a copy of elf/elf.h in glibc, which we periodically sync. It would be good if all projects agree on the constants. I would like to understand where the R_BPF_MAP_FD comes from. But I assume it was a typo for BPF_PSEUDO_MAP_FD from bpf.h (which has the same constant number 1). I'll sent a patch to libc-al...@sourceware.org unless you beat me to it. Thanks, Mark
