linux-kernel - Re: [PATCH v2 15/16] objtool/powerpc: Enable objtool to be built on ppc

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Message-Id: <1662373828.xrnduc1uco.naveen@linux.ibm.com>
Date:   Mon, 05 Sep 2022 16:07:55 +0530
From:   "Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com>
To:     Christophe Leroy <christophe.leroy@...roup.eu>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
        Sathvika Vasireddy <sv@...ux.ibm.com>
Cc:     "aik@...abs.ru" <aik@...abs.ru>,
        "chenzhongjin@...wei.com" <chenzhongjin@...wei.com>,
        "Elliott, Robert (Servers)" <elliott@....com>,
        "jpoimboe@...hat.com" <jpoimboe@...hat.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "mbenes@...e.cz" <mbenes@...e.cz>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "mpe@...erman.id.au" <mpe@...erman.id.au>,
        "npiggin@...il.com" <npiggin@...il.com>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "rostedt@...dmis.org" <rostedt@...dmis.org>
Subject: Re: [PATCH v2 15/16] objtool/powerpc: Enable objtool to be built on
 ppc

Christophe Leroy wrote:
> 
> 
> Le 29/08/2022 à 07:52, Sathvika Vasireddy a écrit :
>> 
>> diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
>> index 4c466acdc70d..dc05cd23c233 100644
>> --- a/arch/powerpc/Kconfig
>> +++ b/arch/powerpc/Kconfig
>> @@ -237,6 +237,7 @@ config PPC
>>   	select HAVE_MOD_ARCH_SPECIFIC
>>   	select HAVE_NMI				if PERF_EVENTS || (PPC64 && PPC_BOOK3S)
>>   	select HAVE_OPTPROBES
>> +	select HAVE_OBJTOOL			if PPC32 || MPROFILE_KERNEL
> 
> Why restrict it to MPROFILE_KERNEL ? In your RFC it was for all PPC64.
> 
> Recent discussion on the list shows new problem with recordmcount, see 
> https://lore.kernel.org/all/MW5PR84MB184250EA1CAE04497C1E7CE9AB769@MW5PR84MB1842.NAMPRD84.PROD.OUTLOOK.COM/
> 
> Those ones are with ppc64 big endian, so objtool would be welcome here 
> as well.

I don't think adding support for objtool on ppc64 elfv1 is a good idea. 
While it might solve the immediate issue with recordmcount, I worry that 
the function descriptors and dot symbols in ppc64 elfv1 might throw up 
issues in the future causing maintenance overhead.


- Naveen