From: Peter Zijlstra <peterz@infradead.org>
To: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Christoph Hellwig <hch@lst.de>,
Randy Dunlap <rdunlap@infradead.org>,
Andrew Morton <akpm@linux-foundation.org>,
broonie@kernel.org, linux-fsdevel@vger.kernel.org,
linux-kernel@vger.kernel.org, linux-mm@kvack.org,
linux-next@vger.kernel.org, mhocko@suse.cz,
mm-commits@vger.kernel.org, sfr@canb.auug.org.au,
Linus Torvalds <torvalds@linux-foundation.org>,
viro@zeniv.linux.org.uk, x86@kernel.org,
Steven Rostedt <rostedt@goodmis.org>
Subject: Re: mmotm 2020-05-13-20-30 uploaded (objtool warnings)
Date: Fri, 29 May 2020 18:12:53 +0200 [thread overview]
Message-ID: <20200529161253.GD706460@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20200529160514.cyaytn33thphb3tz@treble>
On Fri, May 29, 2020 at 11:05:14AM -0500, Josh Poimboeuf wrote:
> It looks to me like GCC is doing the right thing. That likely()
> translates to:
>
> # define likely(x) (__branch_check__(x, 1, __builtin_constant_p(x)))
>
> which becomes:
>
> #define __branch_check__(x, expect, is_constant) ({ \
> long ______r; \
> static struct ftrace_likely_data \
> __aligned(4) \
> __section(_ftrace_annotated_branch) \
> ______f = { \
> .data.func = __func__, \
> .data.file = __FILE__, \
> .data.line = __LINE__, \
> }; \
> ______r = __builtin_expect(!!(x), expect); \
> ftrace_likely_update(&______f, ______r, \
> expect, is_constant); \
> ______r; \
> })
>
> Here 'x' is the call to user_access_begin(). It evaluates 'x' -- and
> thus calls user_access_begin() -- before the call to
> ftrace_likely_update().
>
> So it's working as designed, right? The likely() just needs to be
> changed to likely_notrace().
But if !x (ie we fail user_access_begin()), we should not pass STAC() on
the way to out_err. OTOH if x, we should not be jumping to out_err.
I'm most confused... must not stare at asm for a while.
next prev parent reply other threads:[~2020-05-29 16:15 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20200513175005.1f4839360c18c0238df292d1@linux-foundation.org>
2020-05-14 3:31 ` mmotm 2020-05-13-20-30 uploaded Andrew Morton
2020-05-14 15:30 ` mmotm 2020-05-13-20-30 uploaded (gpu/drm/bridge/sil-sii8620) Randy Dunlap
2020-05-14 15:32 ` mmotm 2020-05-13-20-30 uploaded (objtool warnings) Randy Dunlap
2020-05-14 15:33 ` Randy Dunlap
2020-05-28 15:54 ` Josh Poimboeuf
2020-05-28 17:04 ` Josh Poimboeuf
2020-05-28 17:20 ` Peter Zijlstra
2020-05-29 13:57 ` Christoph Hellwig
2020-05-29 14:35 ` Peter Zijlstra
2020-05-29 14:53 ` Peter Zijlstra
2020-05-29 15:33 ` Peter Zijlstra
2020-05-29 16:05 ` Josh Poimboeuf
2020-05-29 16:12 ` Peter Zijlstra [this message]
2020-05-29 16:50 ` Josh Poimboeuf
2020-05-29 16:54 ` Peter Zijlstra
2020-05-29 17:25 ` [PATCH] x86/uaccess: Remove redundant likely/unlikely annotations Josh Poimboeuf
2020-05-29 18:29 ` Randy Dunlap
2020-05-29 19:31 ` mmotm 2020-05-13-20-30 uploaded (objtool warnings) Linus Torvalds
2020-05-29 20:08 ` Al Viro
2020-05-29 20:14 ` Al Viro
2020-05-15 23:30 ` mmotm 2020-05-15-16-29 uploaded Andrew Morton
2020-05-16 5:53 ` Stephen Rothwell
2020-05-18 23:15 ` Stephen Rothwell
2020-05-20 4:48 ` mmotm 2020-05-19-21-47 uploaded Andrew Morton
2020-05-22 3:43 ` mmotm 2020-05-21-20-42 uploaded Andrew Morton
2020-05-22 16:26 ` mmotm 2020-05-21-20-42 uploaded (atomisp) Randy Dunlap
2020-05-23 3:36 ` mmotm 2020-05-22-20-35 uploaded Andrew Morton
2020-05-23 15:08 ` mmotm 2020-05-22-20-35 uploaded (phy/intel/phy-intel-combo.c) Randy Dunlap
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