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

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Message-ID: <aebad82f-3979-f7e4-a17b-5f943cd0f18b@loongson.cn>
Date: Tue, 26 Nov 2024 19:00:25 +0800
From: Tiezhu Yang <yangtiezhu@...ngson.cn>
To: Josh Poimboeuf <jpoimboe@...nel.org>
Cc: Huacai Chen <chenhuacai@...nel.org>, Peter Zijlstra
 <peterz@...radead.org>, loongarch@...ts.linux.dev,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 04/10] objtool: Handle PC relative relocation type

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@...ngson.cn>
>> ---
>>  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().
>

Will do it.