From: "Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: "aik@ozlabs.ru" <aik@ozlabs.ru>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Sathvika Vasireddy <sv@linux.ibm.com>,
"rostedt@goodmis.org" <rostedt@goodmis.org>,
"jpoimboe@redhat.com" <jpoimboe@redhat.com>,
"mbenes@suse.cz" <mbenes@suse.cz>,
"linuxppc-dev@lists.ozlabs.org" <linuxppc-dev@lists.ozlabs.org>
Subject: Re: [RFC PATCH 1/4] objtool: Add --mnop as an option to --mcount
Date: Thu, 26 May 2022 17:21:02 +0530 [thread overview]
Message-ID: <1653564857.f06fbbl3vg.naveen@linux.ibm.com> (raw)
In-Reply-To: <Yo4UysC69UCwhlYp@hirez.programming.kicks-ass.net>
Peter Zijlstra wrote:
> On Tue, May 24, 2022 at 04:01:48PM +0530, Naveen N. Rao wrote:
>
>> We need to know for sure either way. Nop'ing out the _mcount locations at
>> 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.
>>
>> Do you have a different approach in mind?
>
> 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.
>
> Does that help?
That's an interesting thought. Depending on the type of trampoline the
compiler emits, I might be able to use this approach. We will still need
objtool on powerpc so that we can note down those trampoline locations.
Thanks,
Naveen
WARNING: multiple messages have this Message-ID (diff)
From: "Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com>
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>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"linuxppc-dev@lists.ozlabs.org" <linuxppc-dev@lists.ozlabs.org>,
"mbenes@suse.cz" <mbenes@suse.cz>,
"mpe@ellerman.id.au" <mpe@ellerman.id.au>,
"rostedt@goodmis.org" <rostedt@goodmis.org>,
Sathvika Vasireddy <sv@linux.ibm.com>
Subject: Re: [RFC PATCH 1/4] objtool: Add --mnop as an option to --mcount
Date: Thu, 26 May 2022 17:21:02 +0530 [thread overview]
Message-ID: <1653564857.f06fbbl3vg.naveen@linux.ibm.com> (raw)
In-Reply-To: <Yo4UysC69UCwhlYp@hirez.programming.kicks-ass.net>
Peter Zijlstra wrote:
> On Tue, May 24, 2022 at 04:01:48PM +0530, Naveen N. Rao wrote:
>
>> We need to know for sure either way. Nop'ing out the _mcount locations at
>> 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.
>>
>> Do you have a different approach in mind?
>
> 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.
>
> Does that help?
That's an interesting thought. Depending on the type of trampoline the
compiler emits, I might be able to use this approach. We will still need
objtool on powerpc so that we can note down those trampoline locations.
Thanks,
Naveen
next prev parent reply other threads:[~2022-05-26 11:52 UTC|newest]
Thread overview: 49+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-05-23 17:55 [RFC PATCH 0/4] objtool: Enable and implement --mcount option on powerpc Sathvika Vasireddy
2022-05-23 17:55 ` Sathvika Vasireddy
2022-05-23 17:55 ` [RFC PATCH 1/4] objtool: Add --mnop as an option to --mcount Sathvika Vasireddy
2022-05-23 17:55 ` Sathvika Vasireddy
2022-05-24 8:54 ` Christophe Leroy
2022-05-24 8:54 ` Christophe Leroy
2022-05-24 10:15 ` Naveen N. Rao
2022-05-24 10:15 ` Naveen N. Rao
2022-05-24 10:20 ` Christophe Leroy
2022-05-24 10:20 ` Christophe Leroy
2022-05-24 10:31 ` Naveen N. Rao
2022-05-24 10:31 ` Naveen N. Rao
2022-05-25 11:36 ` Peter Zijlstra
2022-05-25 11:36 ` Peter Zijlstra
2022-05-26 11:51 ` Naveen N. Rao [this message]
2022-05-26 11:51 ` Naveen N. Rao
2022-05-23 17:55 ` [RFC PATCH 2/4] objtool: Enable objtool to run only on files with ftrace enabled Sathvika Vasireddy
2022-05-23 17:55 ` Sathvika Vasireddy
2022-05-24 8:57 ` Christophe Leroy
2022-05-24 8:57 ` Christophe Leroy
2022-05-24 10:53 ` Sathvika Vasireddy
2022-05-24 10:53 ` Sathvika Vasireddy
2022-05-24 13:28 ` Christophe Leroy
2022-05-24 13:28 ` Christophe Leroy
2022-05-23 17:55 ` [RFC PATCH 3/4] objtool/powerpc: Enable objtool to be built on ppc Sathvika Vasireddy
2022-05-23 17:55 ` Sathvika Vasireddy
2022-05-24 9:13 ` Christophe Leroy
2022-05-24 9:13 ` Christophe Leroy
2022-05-23 17:55 ` [RFC PATCH 4/4] objtool/powerpc: Add --mcount specific implementation Sathvika Vasireddy
2022-05-23 17:55 ` Sathvika Vasireddy
2022-05-24 9:35 ` Christophe Leroy
2022-05-24 9:35 ` Christophe Leroy
2022-05-24 11:00 ` Sathvika Vasireddy
2022-05-24 11:00 ` Sathvika Vasireddy
2022-05-24 13:33 ` Christophe Leroy
2022-05-24 13:33 ` Christophe Leroy
2022-05-25 17:27 ` Christophe Leroy
2022-05-31 6:20 ` Christophe Leroy
2022-05-31 6:20 ` Christophe Leroy
2022-06-16 13:34 ` Naveen N. Rao
2022-06-16 13:34 ` Naveen N. Rao
2022-06-16 13:40 ` Christophe Leroy
2022-06-16 13:40 ` Christophe Leroy
2022-06-16 13:57 ` Peter Zijlstra
2022-06-16 13:57 ` Peter Zijlstra
2022-06-16 14:06 ` Christophe Leroy
2022-06-16 14:06 ` Christophe Leroy
2022-06-17 14:04 ` Naveen N. Rao
2022-06-17 14:04 ` Naveen N. Rao
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