On 2023-08-29 14:45, Xi Ruoyao wrote:
> On Tue, 2023-08-29 at 14:28 +0800, Tiezhu Yang wrote:
>> The initial aim is to silence the following objtool warnings:
>>
>> arch/loongarch/kernel/fpu.o: warning: objtool: _save_fp_context() falls through to next function fault()
>> arch/loongarch/kernel/fpu.o: warning: objtool: _restore_fp_context() falls through to next function fault()
>> arch/loongarch/kernel/fpu.o: warning: objtool: _save_lsx_context() falls through to next function fault()
>> arch/loongarch/kernel/fpu.o: warning: objtool: _restore_lsx_context() falls through to next function fault()
>> arch/loongarch/kernel/fpu.o: warning: objtool: _save_lasx_context() falls through to next function fault()
>> arch/loongarch/kernel/fpu.o: warning: objtool: _restore_lasx_context() falls through to next function fault()
>>
>> Obviously, the symbol fault is not a function, it is just a local label,
> Hmm why? To me this seems a function. We don't branch to it but store
> its address (a "function pointer") in the extable.
>
> And these warnings do not make any sense to me:
>
> /* snip */
>
>> diff --git a/arch/loongarch/kernel/fpu.S b/arch/loongarch/kernel/fpu.S
>> index b4032de..7defe50 100644
>> --- a/arch/loongarch/kernel/fpu.S
>> +++ b/arch/loongarch/kernel/fpu.S
>> @@ -521,7 +521,7 @@ SYM_FUNC_START(_restore_lasx_context)
>> jr ra
> _restore_lasx_context returns with this instruction. How can it fall
> through into fault?
I think it is because objtool will check ex_table. Something special
here. (in special.c)
So this function control flow reaches another global function, caused
warning. (Just some impressions)
Thanks,
Jinyang
>
>> SYM_FUNC_END(_restore_lasx_context)
>> -SYM_FUNC_START(fault)
>> +SYM_CODE_START_LOCAL(fault)
>> li.w a0, -EFAULT # failure
>> jr ra
>> -SYM_FUNC_END(fault)
>> +SYM_CODE_END(fault)