With CONFIG_CFI_CLANG, the compiler replaces function references with references to the CFI jump table, which confuses objtool. This change, based on Josh's initial patch [1], goes through the list of relocations and replaces jump table symbols with the actual function symbols.
[1] https://lore.kernel.org/r/d743f4b36e120c06506567a9f87a062ae03da47f.1611263462.git.jpoim...@redhat.com/ Reported-by: Sedat Dilek <sedat.di...@gmail.com> Suggested-by: Josh Poimboeuf <jpoim...@redhat.com> Signed-off-by: Sami Tolvanen <samitolva...@google.com> --- tools/objtool/elf.c | 48 +++++++++++++++++++++++++++++ tools/objtool/include/objtool/elf.h | 2 +- 2 files changed, 49 insertions(+), 1 deletion(-) diff --git a/tools/objtool/elf.c b/tools/objtool/elf.c index d08f5f3670f8..5cf2c61ce7b8 100644 --- a/tools/objtool/elf.c +++ b/tools/objtool/elf.c @@ -273,6 +273,10 @@ static int read_sections(struct elf *elf) } sec->len = sec->sh.sh_size; + /* Detect -fsanitize=cfi jump table sections */ + if (!strncmp(sec->name, ".text..L.cfi.jumptable", 22)) + sec->cfi_jt = true; + list_add_tail(&sec->list, &elf->sections); elf_hash_add(elf->section_hash, &sec->hash, sec->idx); elf_hash_add(elf->section_name_hash, &sec->name_hash, str_hash(sec->name)); @@ -548,6 +552,48 @@ static int read_rela_reloc(struct section *sec, int i, struct reloc *reloc, unsi return 0; } +static int fix_cfi_relocs(const struct elf *elf) +{ + struct section *sec, *tmpsec; + struct reloc *reloc, *tmpreloc; + + list_for_each_entry_safe(sec, tmpsec, &elf->sections, list) { + list_for_each_entry_safe(reloc, tmpreloc, &sec->reloc_list, list) { + struct symbol *sym; + struct reloc *func_reloc; + + /* + * CONFIG_CFI_CLANG replaces function relocations to refer + * to an intermediate jump table. Undo the conversion so + * objtool can make sense of things. + */ + if (!reloc->sym->sec->cfi_jt) + continue; + + if (reloc->sym->type == STT_SECTION) + sym = find_func_by_offset(reloc->sym->sec, + reloc->addend); + else + sym = reloc->sym; + + if (!sym || !sym->sec) + continue; + + /* + * The jump table immediately jumps to the actual function, + * so look up the relocation there. + */ + func_reloc = find_reloc_by_dest_range(elf, sym->sec, sym->offset, 5); + if (!func_reloc || !func_reloc->sym) + continue; + + reloc->sym = func_reloc->sym; + } + } + + return 0; +} + static int read_relocs(struct elf *elf) { struct section *sec; @@ -608,6 +654,8 @@ static int read_relocs(struct elf *elf) tot_reloc += nr_reloc; } + fix_cfi_relocs(elf); + if (stats) { printf("max_reloc: %lu\n", max_reloc); printf("tot_reloc: %lu\n", tot_reloc); diff --git a/tools/objtool/include/objtool/elf.h b/tools/objtool/include/objtool/elf.h index 45e5ede363b0..ef19578fc5e4 100644 --- a/tools/objtool/include/objtool/elf.h +++ b/tools/objtool/include/objtool/elf.h @@ -39,7 +39,7 @@ struct section { char *name; int idx; unsigned int len; - bool changed, text, rodata, noinstr; + bool changed, text, rodata, noinstr, cfi_jt; }; struct symbol { -- 2.31.1.368.gbe11c130af-goog
