Messages in this thread | | | Date | Thu, 14 Oct 2021 12:22:26 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH v5 01/15] objtool: Add CONFIG_CFI_CLANG support |
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On Wed, Oct 13, 2021 at 11:16:44AM -0700, Sami Tolvanen wrote: > diff --git a/tools/objtool/arch/x86/decode.c b/tools/objtool/arch/x86/decode.c > index 1f2ae708b223..5fe31523e51f 100644 > --- a/tools/objtool/arch/x86/decode.c > +++ b/tools/objtool/arch/x86/decode.c > @@ -63,6 +63,23 @@ bool arch_callee_saved_reg(unsigned char reg) > } > } > > +unsigned long arch_cfi_section_reloc_offset(struct reloc *reloc) > +{ > + if (!reloc->addend) > + return 0; > + > + if (reloc->type == R_X86_64_PC32 || reloc->type == R_X86_64_PLT32) > + return reloc->addend + 4; > + > + return reloc->addend; > +} > + > +unsigned long arch_cfi_jump_reloc_offset(unsigned long offset) > +{ > + /* offset to the relocation in a jmp instruction */ > + return offset + 1; > +} > + > unsigned long arch_dest_reloc_offset(int addend) > { > return addend + 4; > diff --git a/tools/objtool/elf.c b/tools/objtool/elf.c > index b18f0055b50b..cd09c93c34fb 100644 > --- a/tools/objtool/elf.c > +++ b/tools/objtool/elf.c
> @@ -575,6 +580,49 @@ static int read_rela_reloc(struct section *sec, int i, struct reloc *reloc, unsi > return 0; > } > > +/* > + * CONFIG_CFI_CLANG replaces function relocations to refer to an intermediate > + * jump table. Undo the conversion so objtool can make sense of things. > + */ > +static int fix_cfi_relocs(const struct elf *elf) > +{ > + struct section *sec; > + struct reloc *reloc; > + > + list_for_each_entry(sec, &elf->sections, list) { > + list_for_each_entry(reloc, &sec->reloc_list, list) { > + struct reloc *cfi_reloc; > + unsigned long offset; > + > + if (!reloc->sym->sec->cfi_jt) > + continue; > + > + if (reloc->sym->type == STT_SECTION) > + offset = arch_cfi_section_reloc_offset(reloc); > + else > + offset = reloc->sym->offset; > + > + /* > + * The jump table immediately jumps to the actual function, > + * so look up the relocation there. > + */ > + offset = arch_cfi_jump_reloc_offset(offset); > + cfi_reloc = find_reloc_by_dest(elf, reloc->sym->sec, offset); > + > + if (!cfi_reloc || !cfi_reloc->sym) { > + WARN("can't find a CFI jump table relocation at %s+0x%lx", > + reloc->sym->sec->name, offset); > + return -1; > + } > + > + reloc->sym = cfi_reloc->sym; > + reloc->addend = 0; > + } > + } > + > + return 0; > +}
If that section ever gets modified and we end up running elf_rebuild_reloc_section() on it, we're in trouble, right?
Do we want a fatal error in elf_rebuild_reloc_section() when ->cfi_jt is set?
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