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Date:   Mon, 05 Sep 2022 16:25:42 +0530
From:   "Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com>
Subject: Re: [PATCH v2 11/16] objtool: Add --mnop as an option to --mcount
To:     Peter Zijlstra <peterz@infradead.org>,
        Sathvika Vasireddy <sv@linux.ibm.com>
Cc:     aik@ozlabs.ru, chenzhongjin@huawei.com,
        christophe.leroy@csgroup.eu, jpoimboe@redhat.com,
        linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org,
        mbenes@suse.cz, mingo@redhat.com, mpe@ellerman.id.au,
        npiggin@gmail.com, rostedt@goodmis.org
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Peter Zijlstra wrote:
> On Mon, Aug 29, 2022 at 11:22:18AM +0530, Sathvika Vasireddy wrote:
>> Architectures can select HAVE_NOP_MCOUNT if they choose
>> to nop out mcount call sites. If that config option is
>> selected, then --mnop is passed as an option to objtool,
>> along with --mcount.
>>=20
>> Also, make sure that --mnop can be passed as an option
>> to objtool only when --mcount is passed.
>>=20
>> Signed-off-by: Sathvika Vasireddy <sv@linux.ibm.com>
>=20
> IIRC you want to nop the things yourself because PLT entries or
> something?

For two reasons:
1. We want to maintain a pointer to 'struct module' as part of the=20
ftrace rec so that we can patch ftrace sites in modules to go to module=20
stubs.
2. We depend on compiler generated long branches to support large=20
kernels.

>=20
> Anyway, patch looks fine, even though the Changelog doesn't relaly
> justify the change.

Sure. We should add that powerpc kernel does not support nop'ed out=20
ftrace locations.

>=20
> Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
>=20

Thanks,
Naveen