ld.lld: warning: vmlinux.a(drivers/i2c/busses/i2c-i801.o):(.discard.retpoline_safe+0x120): has non-ABS relocation R_386_PC32 against symbol ''

[MaskRay]

I am not familiar with objtool, but it seems that after https://git.kernel.org/linus/1c0c1faf5692c18c127d044ecc0cc92c7bab3477 (objtool: Use relative pointers for annotations) , non-SHF_ALLOC sections like .discard.retpoline_safe may contain PC-relative relocations:

% readelf -Wr arch/x86/kernel/irq_32.o
...
Relocation section '.rel.discard.retpoline_safe' at offset 0x3d8 contains 4 entries:
 Offset     Info    Type                Sym. Value  Symbol's Name
00000000  00000202 R_386_PC32             00000000   .text
00000004  00000302 R_386_PC32             00000000   .altinstr_replacement
00000008  00000202 R_386_PC32             00000000   .text
0000000c  00000302 R_386_PC32             00000000   .altinstr_replacement

In the ELF object file format, non-SHF_ALLOC sections do not occupy memory during program execution. Such sections referencing SHF_ALLOC sections (.text) do not make sense.

Currently LLD report warnings for non-relocatable links and suppresses the warnings for relocatable links.
After llvm/llvm-project#66804, in relocatable links, SHT_REL PC-relative relocations will get warnings as well.
LLD still doesn't report warnings for SHT_RELA PC-relative relocations. LLD doesn't mostly because we don't want to spend more code on the diagnostic.

[nickdesaulniers]

Further background, after applying llvm/llvm-project#66804
I see a few hundred warnings like:

ld.lld: warning: vmlinux.a(drivers/i2c/busses/i2c-i801.o):(.discard.retpoline_safe+0x120): has non-ABS relocation R_386_PC32 against symbol ''

Thanks for bisecting the kernel to find a culprit. Looking at that commit, I wonder then if perhaps ANNOTATE_RETPOLINE_SAFE, ANNOTATE_NOENDBR, ANNOTATE_INTRA_FUNCTION_CALL, UNWIND_HINT, or STACK_FRAME_NON_STANDARD is being used in a non-SHF_ALLOC section then?

cc @jpoimboe

[nickdesaulniers]

Or is it that the sections modified in 1c0c1fa that aren't "a" should not have been changed?