Re: The trouble with __weak and objtool got worse

[Josh Poimboeuf <jpoimboe@redhat.com>]

On Sat, Apr 16, 2022 at 12:48:09PM +0200, Peter Zijlstra wrote:
> This *might* work for static_call. But what about things like
> .retpoline_sites?
> 
> If we get an indirect inside the weak function and at
> a different place inside the non-weak function, then we end up with two
> patch sites in the non-weak function.
> 
> And since all of that is compiler generated, we don't have anything to
> stick anything in to alleviate trouble.
> 
> (in fact, I didn't observe this with static_call, I just picked it for
> the example because it was somewhat easier)

Ok, right.  And ORC entries will be broken.  I found the ones below by
disabling CONFIG_DEBUG_INFO and looking for "sym->bind == STB_WEAK" in
the elf_add_reloc_to_insn() fallback.

I guess objtool will need to bite the bullet and create section symbols.

  lib/clz_ctz.o: warning: objtool: .orc_unwind_ip+0x0: missing section symbol for reference to weak function text
  lib/clz_ctz.o: warning: objtool: .orc_unwind_ip+0x4: missing section symbol for reference to weak function text
  lib/clz_ctz.o: warning: objtool: .orc_unwind_ip+0x8: missing section symbol for reference to weak function text
  lib/clz_ctz.o: warning: objtool: .orc_unwind_ip+0xc: missing section symbol for reference to weak function text
  lib/clz_ctz.o: warning: objtool: .orc_unwind_ip+0x10: missing section symbol for reference to weak function text
  lib/clz_ctz.o: warning: objtool: .orc_unwind_ip+0x14: missing section symbol for reference to weak function text
  lib/iomap_copy.o: warning: objtool: .orc_unwind_ip+0x0: missing section symbol for reference to weak function text
  lib/iomap_copy.o: warning: objtool: .orc_unwind_ip+0x4: missing section symbol for reference to weak function text
  lib/iomap_copy.o: warning: objtool: .orc_unwind_ip+0x10: missing section symbol for reference to weak function text
  lib/iomap_copy.o: warning: objtool: .orc_unwind_ip+0x14: missing section symbol for reference to weak function text
  lib/crc32.o: warning: objtool: .orc_unwind_ip+0x14: missing section symbol for reference to weak function text
  lib/crc32.o: warning: objtool: .orc_unwind_ip+0x18: missing section symbol for reference to weak function text
  lib/crc32.o: warning: objtool: .orc_unwind_ip+0x1c: missing section symbol for reference to weak function text
  lib/crc32.o: warning: objtool: .orc_unwind_ip+0x20: missing section symbol for reference to weak function text
  lib/crc32.o: warning: objtool: .orc_unwind_ip+0x24: missing section symbol for reference to weak function text
  lib/crc32.o: warning: objtool: .orc_unwind_ip+0x28: missing section symbol for reference to weak function text

-- 
Josh