linux-kernel - Re: arch/powerpc/kernel/head_85xx.o: warning: objtool: .head.text+0x1a6c: unannotated intra-function call

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Date:   Wed, 25 Jan 2023 19:31:46 +1100
From:   Michael Ellerman <mpe@...erman.id.au>
To:     "Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com>,
        kernel test robot <lkp@...el.com>,
        Sathvika Vasireddy <sv@...ux.ibm.com>
Cc:     Christophe Leroy <christophe.leroy@...roup.eu>,
        linux-kernel@...r.kernel.org, oe-kbuild-all@...ts.linux.dev,
        linuxppc-dev@...ts.ozlabs.org, npiggin@...il.com
Subject: Re: arch/powerpc/kernel/head_85xx.o: warning: objtool:
 .head.text+0x1a6c: unannotated intra-function call

"Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com> writes:
> Sathvika Vasireddy wrote:
>> 
>>>>> arch/powerpc/kvm/booke.o: warning: objtool: kvmppc_fill_pt_regs+0x30: unannotated intra-function call
>> 
>> As an attempt to fix it, I tried expanding ANNOTATE_INTRA_FUNCTION_CALL 
>> macro to indicate that the branch target is valid. It then threw another 
>> warning (arch/powerpc/kvm/booke.o: warning: objtool: 
>> kvmppc_fill_pt_regs+0x38: intra_function_call not a direct call). The 
>> below diff just removes the warnings for me, but I'm not very sure if 
>> this is the best way to fix the objtool warnings seen with this 
>> particular file. Please let me know if there are any better ways to fix it.
>> 
>> diff --git a/arch/powerpc/kvm/booke.c b/arch/powerpc/kvm/booke.c
>> index 0dce93ccaadf..b6a413824b98 100644
>> --- a/arch/powerpc/kvm/booke.c
>> +++ b/arch/powerpc/kvm/booke.c
>> @@ -917,7 +917,9 @@ static void kvmppc_fill_pt_regs(struct pt_regs *regs)
>>          asm("mr %0, 1" : "=r"(r1));
>>          asm("mflr %0" : "=r"(lr));
>>          asm("mfmsr %0" : "=r"(msr));
>> +       asm(".pushsection .discard.intra_function_calls; .long 999f; 
>> .popsection; 999:");
>>          asm("bl 1f; 1: mflr %0" : "=r"(ip));
>
> I don't think you can assume that there won't be anything in between two 
> asm statements.

Yeah, compiler could interleave something theoretically.

> Even if that works, I don't think it is good to expand the macro here.  
> That asm statement looks to be trying to grab the current nip. I don't 
> know enough about that code, and someone who knows more about KVM may be 
> able to help, but it looks like we should be able to simply set 'ip' to 
> the address of kvmppc_fill_pt_regs()?

There is _THIS_IP_ which should be sufficient.

cheers