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Date:   Thu, 26 May 2022 17:21:02 +0530
From:   "Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com>
Subject: Re: [RFC PATCH 1/4] objtool: Add --mnop as an option to --mcount
To:     Peter Zijlstra <peterz@infradead.org>
Cc:     "aik@ozlabs.ru" <aik@ozlabs.ru>,
        Christophe Leroy <christophe.leroy@csgroup.eu>,
        "jpoimboe@redhat.com" <jpoimboe@redhat.com>,
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        "mpe@ellerman.id.au" <mpe@ellerman.id.au>,
        "rostedt@goodmis.org" <rostedt@goodmis.org>,
        Sathvika Vasireddy <sv@linux.ibm.com>
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Peter Zijlstra wrote:
> On Tue, May 24, 2022 at 04:01:48PM +0530, Naveen N. Rao wrote:
>=20
>> We need to know for sure either way. Nop'ing out the _mcount locations a=
t
>> boot allows us to discover existing long branch trampolines. If we want =
to
>> avoid it, we need to note down those locations during build time.
>>=20
>> Do you have a different approach in mind?
>=20
> If you put _mcount in a separate section then the compiler cannot tell
> where it is and is forced to always emit a long branch trampoline.
>=20
> Does that help?

That's an interesting thought. Depending on the type of trampoline the=20
compiler emits, I might be able to use this approach. We will still need=20
objtool on powerpc  so that we can note down those trampoline locations.


Thanks,
Naveen