From: Michael Ellerman <mpe@ellerman•id.au>
To: Nicholas Piggin <npiggin@gmail•com>,
Sathvika Vasireddy <sv@linux•ibm.com>,
linuxppc-dev@lists•ozlabs.org
Cc: peterz@infradead•org, linux-kernel@vger•kernel.org,
aik@ozlabs•ru, mingo@redhat•com, rostedt@goodmis•org,
jpoimboe@redhat•com, naveen.n.rao@linux•vnet.ibm.com,
mbenes@suse•cz, chenzhongjin@huawei•com
Subject: Re: [PATCH v2 02/16] powerpc: override __ALIGN() and __ALIGN_STR() macros
Date: Wed, 31 Aug 2022 17:22:25 +1000 [thread overview]
Message-ID: <878rn4vpvy.fsf@mpe.ellerman.id.au> (raw)
In-Reply-To: <CMJW5375AS4G.3VZ0XK6D3OZ9O@bobo>
"Nicholas Piggin" <npiggin@gmail•com> writes:
> On Mon Aug 29, 2022 at 3:52 PM AEST, Sathvika Vasireddy wrote:
>> Powerpc instructions must be word-aligned. Currently,
>> there is an alignment of 16 bytes (by default), and it is
>> much more than what is required for powerpc (4 bytes).
>>
>> The default expansion of __ALIGN() macro is:
>> #define __ALIGN .align 4,0x90
>>
>> Since Powerpc Linux does not require a 16 byte alignment,
>> override __ALIGN() and __ALIGN_STR() macros to use required
>> 4 byte alignment.
>
> Alignment can be desirable beyond the minimum requirement, for
> example 16 byte alignment for functions could be helpful for
> instruction fetch. So it should be explained why possible
> benefits of the larger alignment are not worth it.
Using ".align 2" matches what our existing _GLOBAL macro does. So this
change basically just propagates that existing alignment into this new
macro, which is used for similar purposes.
So if we want to increase the alignment we should do that explicitly,
and update _GLOBAL at the same time.
The change log should probably just say ~= "use the same alignment as
the existing _GLOBAL macro".
What's more important, but not mentioned in the change log, is that we
don't want to pad with 0x90, because repeated 0x90s are not a nop or
trap on powerpc.
cheers
next prev parent reply other threads:[~2022-08-31 7:23 UTC|newest]
Thread overview: 64+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-08-29 5:52 [PATCH v2 00/16] objtool: Enable and implement --mcount option on powerpc Sathvika Vasireddy
2022-08-29 5:52 ` [PATCH v2 01/16] powerpc: Replace unreachable() with it's builtin variant in __WARN_FLAGS() Sathvika Vasireddy
2022-08-30 6:15 ` Christophe Leroy
2022-09-05 10:18 ` Naveen N. Rao
2022-08-29 5:52 ` [PATCH v2 02/16] powerpc: override __ALIGN() and __ALIGN_STR() macros Sathvika Vasireddy
2022-08-29 13:26 ` Christophe Leroy
2022-08-29 14:39 ` Sathvika Vasireddy
2022-08-31 3:24 ` Nicholas Piggin
2022-08-31 7:22 ` Michael Ellerman [this message]
2022-09-05 11:03 ` Peter Zijlstra
2022-08-29 5:52 ` [PATCH v2 03/16] powerpc: Fix objtool unannotated intra-function call warnings Sathvika Vasireddy
2022-08-30 6:16 ` Christophe Leroy
2022-08-30 12:42 ` Christophe Leroy
2022-09-05 11:02 ` Peter Zijlstra
2022-08-29 5:52 ` [PATCH v2 04/16] powerpc: Curb objtool unannotated intra-function warnings Sathvika Vasireddy
2022-08-30 6:26 ` Christophe Leroy
2022-08-29 5:52 ` [PATCH v2 05/16] powerpc: Skip objtool from running on drivers/crypto/vmx/aesp8-ppc.o Sathvika Vasireddy
2022-08-30 6:26 ` Christophe Leroy
2022-09-01 19:17 ` Peter Zijlstra
2022-09-05 10:47 ` Naveen N. Rao
2022-08-29 5:52 ` [PATCH v2 06/16] powerpc: Fix objtool unannotated intra-function call warnings on PPC32 Sathvika Vasireddy
2022-08-29 5:52 ` [PATCH v2 07/16] powerpc: Skip objtool from running on VDSO files Sathvika Vasireddy
2022-08-30 6:27 ` Christophe Leroy
2022-09-01 19:19 ` Peter Zijlstra
2022-09-02 7:40 ` Michael Ellerman
2022-08-29 5:52 ` [PATCH v2 08/16] objtool: Fix SEGFAULT Sathvika Vasireddy
2022-09-01 19:20 ` Peter Zijlstra
2022-09-02 8:06 ` Christophe Leroy
2022-09-02 8:42 ` Peter Zijlstra
2022-08-29 5:52 ` [PATCH v2 09/16] objtool: Use target file endianness instead of a compiled constant Sathvika Vasireddy
2022-09-01 19:22 ` Peter Zijlstra
2022-08-29 5:52 ` [PATCH v2 10/16] objtool: Use target file class size " Sathvika Vasireddy
2022-09-01 19:23 ` Peter Zijlstra
2022-08-29 5:52 ` [PATCH v2 11/16] objtool: Add --mnop as an option to --mcount Sathvika Vasireddy
2022-08-30 6:28 ` Christophe Leroy
2022-09-01 19:25 ` Peter Zijlstra
2022-09-05 10:55 ` Naveen N. Rao
2022-08-29 5:52 ` [PATCH v2 12/16] objtool: Read special sections with alts only when specific options are selected Sathvika Vasireddy
2022-08-30 6:31 ` Christophe Leroy
2022-08-29 5:52 ` [PATCH v2 13/16] objtool: Use macros to define arch specific reloc types Sathvika Vasireddy
2022-08-30 6:33 ` Christophe Leroy
2022-09-01 19:28 ` Peter Zijlstra
2022-08-29 5:52 ` [PATCH v2 14/16] objtool: Add arch specific function arch_ftrace_match() Sathvika Vasireddy
2022-08-30 6:36 ` Christophe Leroy
2022-08-29 5:52 ` [PATCH v2 15/16] objtool/powerpc: Enable objtool to be built on ppc Sathvika Vasireddy
2022-08-30 6:41 ` Christophe Leroy
2022-09-05 10:37 ` Naveen N. Rao
2023-02-04 8:19 ` Randy Dunlap
2023-02-04 8:21 ` Randy Dunlap
2023-02-04 8:30 ` Randy Dunlap
2023-02-04 11:55 ` Christophe Leroy
2023-02-04 13:10 ` Christophe Leroy
2023-02-04 15:47 ` Josh Poimboeuf
2022-09-01 9:32 ` Christophe Leroy
2022-09-01 15:11 ` Segher Boessenkool
2022-09-01 16:38 ` Christophe Leroy
2022-09-01 19:01 ` Peter Zijlstra
2022-08-29 5:52 ` [PATCH v2 16/16] objtool/powerpc: Add --mcount specific implementation Sathvika Vasireddy
2022-08-30 6:44 ` Christophe Leroy
2022-08-31 12:50 ` Christophe Leroy
2022-08-31 17:51 ` Segher Boessenkool
2022-09-05 10:45 ` Naveen N. Rao
2022-09-05 20:43 ` Segher Boessenkool
2022-09-06 6:22 ` Christophe Leroy
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=878rn4vpvy.fsf@mpe.ellerman.id.au \
--to=mpe@ellerman$(echo .)id.au \
--cc=aik@ozlabs$(echo .)ru \
--cc=chenzhongjin@huawei$(echo .)com \
--cc=jpoimboe@redhat$(echo .)com \
--cc=linux-kernel@vger$(echo .)kernel.org \
--cc=linuxppc-dev@lists$(echo .)ozlabs.org \
--cc=mbenes@suse$(echo .)cz \
--cc=mingo@redhat$(echo .)com \
--cc=naveen.n.rao@linux$(echo .)vnet.ibm.com \
--cc=npiggin@gmail$(echo .)com \
--cc=peterz@infradead$(echo .)org \
--cc=rostedt@goodmis$(echo .)org \
--cc=sv@linux$(echo .)ibm.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox