From: Yonghong Song yhs@fb.com
mainline inclusion from mainline-5.14-rc1 commit 9f0c317f6aa12b160103ee3946d79276c14b95e2 category: feature bugzilla: https://gitee.com/openeuler/kernel/issues/I5EUVD CVE: NA
Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?i...
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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@fb.com Signed-off-by: Andrii Nakryiko andrii@kernel.org Acked-by: John Fastabend john.fastabend@gmail.com Link: https://lore.kernel.org/bpf/20210522162341.3687617-1-yhs@fb.com (cherry picked from commit 9f0c317f6aa12b160103ee3946d79276c14b95e2) Signed-off-by: Wang Yufen wangyufen@huawei.com --- 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 a2cc297edb99..777b17b230f8 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 488029cb4e42..bd11c429cd5b 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;