On Wed, Dec 23, 2020 at 03:21:26PM -0800, Nick Desaulniers wrote: > Arnd found a randconfig that produces the warning: > > arch/x86/entry/thunk_64.o: warning: objtool: missing symbol for insn at > offset 0x3e > > when building with LLVM_IAS=1 (use Clang's integrated assembler). Josh > notes: > > With the LLVM assembler stripping the .text section symbol, objtool > has no way to reference this code when it generates ORC unwinder > entries, because this code is outside of any ELF function. > > This behavior was implemented as an optimization in LLVM 5 years ago, > but it's not the first time this has caused issues for objtool. A patch > has been authored against LLVM to revert the behavior, which may or may > not be accepted. Until then use a global symbol for the thunk that way > objtool can generate proper unwind info here with LLVM_IAS=1.
As Fangrui pointed out, the section symbol stripping is useful for when there are a ton of sections like '-ffunction-sections' and '-fdata-sections'. Maybe add that justification to the patch description. We can try to support it, though I suspect other tools may also end up getting surprised. > Cc: Fangrui Song <[email protected]> > Reported-by: Arnd Bergmann <[email protected]> > Suggested-by: Josh Poimboeuf <[email protected]> > Link: https://github.com/ClangBuiltLinux/linux/issues/1209 > Link: https://reviews.llvm.org/D93783 > Signed-off-by: Nick Desaulniers <[email protected]> Code looks familiar ;-) Acked-by: Josh Poimboeuf <[email protected]> -- Josh
