[PATCH v2] backends,bpf: add proper relocation support
Wed Jun 20 11:41:00 GMT 2018
On Sat, 2018-06-16 at 13:02 -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".
> The bpf relocations are defined in
> 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.
> Signed-off-by: Yonghong Song <firstname.lastname@example.org>
> backends/ChangeLog | 7 +++++
> backends/Makefile.am | 2 +-
> backends/bpf_init.c | 1 +
> backends/bpf_reloc.def | 3 +-
> backends/bpf_symbol.c | 54
> libelf/elf.h | 3 +-
> tests/ChangeLog | 9 ++++++
> tests/Makefile.am | 5 +++-
> tests/run-reloc-bpf.sh | 33 ++++++++++++++++++++++
> tests/testfile-bpf-reloc.expect.bz2 | Bin 0 -> 300 bytes
> tests/testfile-bpf-reloc.o.bz2 | Bin 0 -> 933 bytes
> 11 files changed, 113 insertions(+), 4 deletions(-)
> create mode 100644 backends/bpf_symbol.c
> create mode 100755 tests/run-reloc-bpf.sh
> create mode 100644 tests/testfile-bpf-reloc.expect.bz2
> create mode 100644 tests/testfile-bpf-reloc.o.bz2
> I didn't add the Changelog to libelf/elf.h as I anticipate the
> change will come from sync'ing with glibc.
> If this patch version looks good, I can send another revision
> once the libelf/elf.h is synced.
The patch looks perfect. And the new testcase is good. I used the
testfile to quickly test eu-readelf --debug-dump also got the
relocations right, and it did of course.
Just waiting for the glibc elf.h update/sync and then I'll push this to
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