Re: [PATCH v4 04/10] objtool: Handle PC relative relocation type

From: Josh Poimboeuf
Date: Tue Nov 26 2024 - 02:19:45 EST


On Fri, Nov 22, 2024 at 12:49:59PM +0800, Tiezhu Yang wrote:
> When compling with Clang on LoongArch, there exists 32 bit PC relative
> relocation type, it needs to get the offset with "S + A - PC" according
> to the spec of "ELF for the LoongArch Architecture".
>
> This is preparation for later patch on LoongArch, there is no effect for
> the other archs with this patch.
>
> Link: https://github.com/loongson/la-abi-specs/blob/release/laelf.adoc
> Signed-off-by: Tiezhu Yang <yangtiezhu@xxxxxxxxxxx>
> ---
> tools/objtool/check.c | 5 +++++
> 1 file changed, 5 insertions(+)
>
> diff --git a/tools/objtool/check.c b/tools/objtool/check.c
> index 19d1263e64e4..8733ca620cca 100644
> --- a/tools/objtool/check.c
> +++ b/tools/objtool/check.c
> @@ -2126,6 +2126,11 @@ static int add_jump_table(struct objtool_file *file, struct instruction *insn,
> if (reloc->sym->type == STT_SECTION) {
> /* Addend field in the relocation entry associated with the symbol */
> offset = reloc_addend(reloc);
> + /* Handle the special cases compiled with Clang on LoongArch */
> + if (file->elf->ehdr.e_machine == EM_LOONGARCH &&
> + reloc_type(reloc) == R_LARCH_32_PCREL)
> + offset = reloc->sym->offset + reloc_addend(reloc) -
> + (reloc_offset(reloc) - reloc_offset(table));

Please, no more "special cases". It makes the common code unreadable.
We should avoid checking 'elf->ehdr.e_machine' in check.c.

Maybe there should be an arch-specific function arch_adjusted_addend().

--
Josh