| Message ID | 20240506155537.it.760-kees@kernel.org (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | [v2] objtool: Report section name in elf_init_reloc_text_sym() warning | expand |
On Mon, May 06, 2024 at 08:55:54AM -0700, Kees Cook wrote: > While tracking down issues with LKDTM's .rodata "function", I found > the warning from elf_init_reloc_text_sym() to be unhelpful because it > wasn't clear which calling path it was coming from. Report the sec->name > and rephrase the warning a bit. Additionally check for NULL sym->name, > which may happen. Hm, as far as I know sym->name shouldn't ever be NULL. Though, looking at this code again I'm realizing that 'sym' could be NULL because it refers to the symbol for the function's *section* rather than for the function itself. And sometimes the toolchain doesn't generate symbols for some sections, if they're not referenced anywhere. (Note the code immediately below your patch actually makes a section symbol if it doesn't exist.) But also, this warning doesn't even need the section's symbol. It can just get the name from the section directly (insn_sec->name). And it would probably also be useful to print the offset (insn_off), like ".rodata+0x1234". Though, even better, we have an offstr() helper which can pretty-print the name of the function or variable, if one exists at that address. tl;dr, does the following work? WARN("%s: unexpected reference to non-executable '%s'", sec->name, offstr(insn_sec, insn_off));
diff --git a/tools/objtool/elf.c b/tools/objtool/elf.c index 3d27983dc908..b38cedd4fd55 100644 --- a/tools/objtool/elf.c +++ b/tools/objtool/elf.c @@ -891,8 +891,8 @@ struct reloc *elf_init_reloc_text_sym(struct elf *elf, struct section *sec, int addend = insn_off; if (!(insn_sec->sh.sh_flags & SHF_EXECINSTR)) { - WARN("bad call to %s() for data symbol %s", - __func__, sym->name); + WARN("%s: unexpected reference to non-executable symbol '%s'", + sec->name, sym->name ?: "<unknown>"); return NULL; }
While tracking down issues with LKDTM's .rodata "function", I found the warning from elf_init_reloc_text_sym() to be unhelpful because it wasn't clear which calling path it was coming from. Report the sec->name and rephrase the warning a bit. Additionally check for NULL sym->name, which may happen. Before: vmlinux.o: warning: objtool: bad call to elf_init_reloc_text_sym() for data symbol .rodata After: vmlinux.o: warning: objtool: .cfi_sites: unexpected reference to non-executable symbol '.rodata' Signed-off-by: Kees Cook <keescook@chromium.org> --- Cc: Josh Poimboeuf <jpoimboe@kernel.org> Cc: Peter Zijlstra <peterz@infradead.org> v1: https://lore.kernel.org/lkml/20240430235106.work.680-kees@kernel.org/ --- tools/objtool/elf.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)