linux-kernel - Re: [RFC PATCH] objtool: Skip unannotated intra-function call warning for bl+mflr pattern

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Message-ID: <7d23db63-6909-48e2-8262-fb000aa714a5@csgroup.eu>
Date: Tue, 25 Feb 2025 08:35:38 +0100
From: Christophe Leroy <christophe.leroy@...roup.eu>
To: Nathan Chancellor <nathan@...nel.org>
Cc: Sathvika Vasireddy <sv@...ux.ibm.com>, jpoimboe@...nel.org,
 peterz@...radead.org, npiggin@...il.com, maddy@...ux.ibm.com,
 linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
 llvm@...ts.linux.dev
Subject: Re: [RFC PATCH] objtool: Skip unannotated intra-function call warning
 for bl+mflr pattern



Le 24/02/2025 à 18:09, Nathan Chancellor a écrit :
> On Mon, Feb 24, 2025 at 02:19:14PM +0100, Christophe Leroy wrote:
>> Well, this problem already exists on clang 18 it seems:
>>
>> 00000004 <btext_map>:
>>     4:   7c 08 02 a6     mflr    r0
>>     8:   94 21 ff e0     stwu    r1,-32(r1)
>>     c:   93 c1 00 18     stw     r30,24(r1)
>>    10:   90 01 00 24     stw     r0,36(r1)
>>    14:   93 a1 00 14     stw     r29,20(r1)
>>    18:   48 00 00 05     bl      1c <btext_map+0x18>
>>    1c:   38 a0 00 00     li      r5,0
>>    20:   7f c8 02 a6     mflr    r30
>>
>> While GCC generates:
>>
>> 00000418 <btext_map>:
>>   418:   94 21 ff e0     stwu    r1,-32(r1)
>>   41c:   7c 08 02 a6     mflr    r0
>>   420:   42 9f 00 05     bcl     20,4*cr7+so,424 <btext_map+0xc>
>>   424:   39 20 00 00     li      r9,0
>>   428:   93 c1 00 18     stw     r30,24(r1)
>>   42c:   7f c8 02 a6     mflr    r30
>>
>> So lets make the kernel tolerate it allthough it should be fixed on clang at
>> the end.
>>
>> I can't find any related issue in the clang issues database
>> (https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com%2Fllvm%2Fllvm-project%2Fissues&data=05%7C02%7Cchristophe.leroy%40csgroup.eu%7C3c10d37fecd94c692acb08dd54f5ff51%7C8b87af7d86474dc78df45f69a2011bb5%7C0%7C0%7C638760137702082512%7CUnknown%7CTWFpbGZsb3d8eyJFbXB0eU1hcGkiOnRydWUsIlYiOiIwLjAuMDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWFpbCIsIldUIjoyfQ%3D%3D%7C0%7C%7C%7C&sdata=qOjbONjWUuXFKUNb42yEPXgXmvU6x%2BuwbGSg2Ep6WRk%3D&reserved=0), should we open one ?
> 
> Yes please, especially if you happen to have a simplified reproducer
> (but no worries if not). I can make sure it gets labeled for the PowerPC
> backend folks to take a look at.
> 

Done, see https://github.com/llvm/llvm-project/issues/128644