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Date: Thu, 10 Oct 2013 10:45:35 +0200
From: Ingo Molnar <mingo@...nel.org>
To: Jakub Jelinek <jakub@...hat.com>
Cc: Peter Zijlstra <peterz@...radead.org>,
Oleg Nesterov <oleg@...hat.com>,
Fengguang Wu <fengguang.wu@...el.com>,
Linus Torvalds <torvalds@...ux-foundation.org>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
Richard Henderson <rth@...ddle.net>
Subject: Re: [PATCH] gcc4: Add 'asm goto' miscompilation quirk
* Jakub Jelinek <jakub@...hat.com> wrote:
> On Thu, Oct 10, 2013 at 10:24:30AM +0200, Ingo Molnar wrote:
> > Something like the patch below? (Totally untested and all that.)
> >
> > Notes:
> >
> > - If the bug is fixed in 4.8.3 then the version check can be sharpened
> > from 99999 to 40803.
>
> The bug is likely going to be fixed already for 4.8.2 (to be released
> next week or so).
>
> > - I'd really prefer this quirk versus having to add the extra barrier to
> > the label, as it makes the actual usage sites a lot less painful.
>
> Please check how much it bloats the generated code.
on Linus's latest tree plain 'asm goto' is only rarely used, so the size
impact of the patch, on x86-64 defconfig, is zero:
vmlinux:
text data bss dec hex filename
11166823 1448024 1187840 13802687 d29cbf vmlinux.before
11166823 1448024 1187840 13802687 d29cbf vmlinux.after
1f7c3c1fd71b4b1327965bcfbc7a77fb vmlinux.before
3b246add801bc170e47096b712942395 vmlinux.after
Using GCC 4.8.1.
> Also, for the bitops patch, you probably want an asm_volatile_goto variant.
Also, for mutex_64.h - good point, will fix that.
Thanks,
Ingo
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