linux-kernel - Re: [PATCH v2 16/16] objtool/powerpc: Add --mcount specific implementation

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Date:   Tue, 6 Sep 2022 06:22:09 +0000
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     Segher Boessenkool <segher@...nel.crashing.org>,
        "Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com>
CC:     "aik@...abs.ru" <aik@...abs.ru>,
        "chenzhongjin@...wei.com" <chenzhongjin@...wei.com>,
        "jpoimboe@...hat.com" <jpoimboe@...hat.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
        "mbenes@...e.cz" <mbenes@...e.cz>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "npiggin@...il.com" <npiggin@...il.com>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "rostedt@...dmis.org" <rostedt@...dmis.org>,
        Sathvika Vasireddy <sv@...ux.ibm.com>
Subject: Re: [PATCH v2 16/16] objtool/powerpc: Add --mcount specific
 implementation



Le 05/09/2022 à 22:43, Segher Boessenkool a écrit :
> Hi!
> 
> On Mon, Sep 05, 2022 at 04:15:07PM +0530, Naveen N. Rao wrote:
>> Segher Boessenkool wrote:
>>>>> +		if ((insn & 3) == 1) {
>>>>> +			*type = INSN_CALL;
>>>>> +			*immediate = insn & 0x3fffffc;
>>>>> +			if (*immediate & 0x2000000)
>>>>> +				*immediate -= 0x4000000;
>>>>> +		}
>>>>> +		break;
>>>>> +	}
>>>
>>> Does this handle AA=1 correctly at all?  That is valid both with and
>>> without relocations, just like AA=0.  Same for AA=1 LK=0 btw.
>>>
>>> If you only handle AA=0, the code should explicitly test for that.
>>
>> The code does test for AA=0 LK=1 with the if statement there?
> 
> Yes, but that is not what I said :-)
> 
> It may be fine to not *handle* AA=1 at all, but the code should at least
> scream bloody murder when it encounters it anyway :-)
> 


By the way, I proposed a cleanup patch that handles it, see 
https://patchwork.ozlabs.org/project/linuxppc-dev/patch/ebe11b73d1015a17034a2c4bedf093fa57f5d29f.1662032631.git.christophe.leroy@csgroup.eu/

Christophe