linux-kernel - Re: [PATCH v4 03/10] objtool: Handle different entry size of rodata

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Message-ID: <e56d48c6-172d-5b31-86de-98384fe58e98@loongson.cn>
Date: Tue, 26 Nov 2024 18:59:38 +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 03/10] objtool: Handle different entry size of rodata

On 11/26/2024 03:02 PM, Josh Poimboeuf wrote:
> On Fri, Nov 22, 2024 at 12:49:58PM +0800, Tiezhu Yang wrote:
>> @@ -2107,8 +2112,15 @@ static int add_jump_table(struct objtool_file *file, struct instruction *insn,
>>  		if (reloc != table && reloc == next_table)
>>  			break;
>>
>> +		/* Handle the special cases compiled with Clang on LoongArch */
>
> This comment is not helpful at all.  A comment is only needed if the
> code is not already obvious.  In that case it should describe what is
> being done and why.

Will remove it.

>> +		if (file->elf->ehdr.e_machine == EM_LOONGARCH &&
>> +		    reloc_type(reloc) == R_LARCH_32_PCREL)
>> +			rodata_entry_size = 4;
>> +		else
>> +			rodata_entry_size = 8;
>
> Is this really loongarch-specific or is it only related to the size of
> the reloc?

This is related with the reloc type, but it may be wrong to only
check the reloc type to assign the value of rodata_entry_size,
becasue the value of reloc type for different archs may be same,
so it needs to check ehdr.e_machine and relocation type.

> Can this be abstracted out to a reloc_size() function like
> so?
>
>   https://git.kernel.org/pub/scm/linux/kernel/git/jpoimboe/linux.git/tree/tools/objtool/klp-diff.c?h=objtool-diff#n834
>
> maybe it could live in elf.h.

OK, if I understand your comment correctly, this should be an
arch-specific function defined in 
tools/objtool/arch/*/include/arch/elf.h, otherwise it also needs to 
check ehdr.e_machine
in tools/objtool/include/objtool/elf.h.

Thanks,
Tiezhu