On Sat, May 22, 2021 at 9:23 AM Yonghong Song <yhs@xxxxxx> wrote: > > LLVM patch https://reviews.llvm.org/D102712 > narrowed the scope of existing R_BPF_64_64 > and R_BPF_64_32 relocations, and added three > new relocations, R_BPF_64_ABS64, R_BPF_64_ABS32 > and R_BPF_64_NODYLD32. The main motivation is > to make relocations linker friendly. > > This change, unfortunately, breaks libbpf build, > and we will see errors like below: > libbpf: ELF relo #0 in section #6 has unexpected type 2 in > /home/yhs/work/bpf-next/tools/testing/selftests/bpf/bpf_tcp_nogpl.o > Error: failed to link > '/home/yhs/work/bpf-next/tools/testing/selftests/bpf/bpf_tcp_nogpl.o': > Unknown error -22 (-22) > The new relocation R_BPF_64_ABS64 is generated > and libbpf linker sanity check doesn't understand it. > Relocation section '.rel.struct_ops' at offset 0x1410 contains 1 entries: > Offset Info Type Symbol's Value Symbol's Name > 0000000000000018 0000000700000002 R_BPF_64_ABS64 0000000000000000 nogpltcp_init > > Look at the selftests/bpf/bpf_tcp_nogpl.c, > void BPF_STRUCT_OPS(nogpltcp_init, struct sock *sk) > { > } > > SEC(".struct_ops") > struct tcp_congestion_ops bpf_nogpltcp = { > .init = (void *)nogpltcp_init, > .name = "bpf_nogpltcp", > }; > The new llvm relocation scheme categorizes 'nogpltcp_init' reference > as R_BPF_64_ABS64 instead of R_BPF_64_64 which is used to specify > ld_imm64 relocation in the new scheme. > > Let us fix the linker sanity checking by including > R_BPF_64_ABS64 and R_BPF_64_ABS32. There is no need to > check R_BPF_64_NODYLD32 which is used for .BTF and .BTF.ext. > > Signed-off-by: Yonghong Song <yhs@xxxxxx> > --- LGTM. Is there a chance that those relocations will get renamed or expanded before LLVM diff lands? Or it's safe to apply now and LLVM side won't change much? > tools/lib/bpf/libbpf_internal.h | 6 ++++++ > tools/lib/bpf/linker.c | 3 ++- > 2 files changed, 8 insertions(+), 1 deletion(-) > > diff --git a/tools/lib/bpf/libbpf_internal.h b/tools/lib/bpf/libbpf_internal.h > index 55d9b4dca64f..e2db08573bf0 100644 > --- a/tools/lib/bpf/libbpf_internal.h > +++ b/tools/lib/bpf/libbpf_internal.h > @@ -28,6 +28,12 @@ > #ifndef R_BPF_64_64 > #define R_BPF_64_64 1 > #endif > +#ifndef R_BPF_64_ABS64 > +#define R_BPF_64_ABS64 2 > +#endif > +#ifndef R_BPF_64_ABS32 > +#define R_BPF_64_ABS32 3 > +#endif > #ifndef R_BPF_64_32 > #define R_BPF_64_32 10 > #endif > diff --git a/tools/lib/bpf/linker.c b/tools/lib/bpf/linker.c > index b594a88620ce..1dca41a24f75 100644 > --- a/tools/lib/bpf/linker.c > +++ b/tools/lib/bpf/linker.c > @@ -892,7 +892,8 @@ static int linker_sanity_check_elf_relos(struct src_obj *obj, struct src_sec *se > size_t sym_idx = ELF64_R_SYM(relo->r_info); > size_t sym_type = ELF64_R_TYPE(relo->r_info); > > - if (sym_type != R_BPF_64_64 && sym_type != R_BPF_64_32) { > + if (sym_type != R_BPF_64_64 && sym_type != R_BPF_64_32 && > + sym_type != R_BPF_64_ABS64 && sym_type != R_BPF_64_ABS32) { > pr_warn("ELF relo #%d in section #%zu has unexpected type %zu in %s\n", > i, sec->sec_idx, sym_type, obj->filename); > return -EINVAL; > -- > 2.30.2 >
