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

From: Tiezhu Yang
Date: Tue Nov 26 2024 - 08:25:10 EST


On 11/26/2024 07:00 PM, Tiezhu Yang wrote:
On 11/26/2024 03:19 PM, Josh Poimboeuf wrote:
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.

OK.


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

Add adjust_offset() in
tools/objtool/include/objtool/elf.h,
like this:

static inline unsigned long adjust_offset(struct elf *elf, struct reloc *reloc,
unsigned long offset)
{
if (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));

return offset;
}

then call it in check.c, like this:

offset = reloc->sym->offset + reloc_addend(reloc);
offset = adjust_offset(file->elf, reloc, offset);

What do you think?

Thanks,
Tiezhu