From: Josh Poimboeuf <jpoimboe@redhat.com>
To: Peter Zijlstra <peterz@infradead.org>
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 11:05:14 -0500 [thread overview]
Message-ID: <20200529160514.cyaytn33thphb3tz@treble> (raw)
In-Reply-To: <20200529153336.GC706518@hirez.programming.kicks-ass.net>
On Fri, May 29, 2020 at 05:33:36PM +0200, Peter Zijlstra wrote:
> On Fri, May 29, 2020 at 04:53:25PM +0200, Peter Zijlstra wrote:
> > On Fri, May 29, 2020 at 04:35:56PM +0200, Peter Zijlstra wrote:
>
> > *groan*, this is one of those CONFIG_PROFILE_ALL_BRANCHES builds. If I
> > disable that it goes away.
> >
> > Still trying to untangle the mess it generated, but on first go it
> > looks like objtool is right, but I'm not sure what went wrong.
>
> $ tools/objtool/objtool check -fab arch/x86/lib/csum-wrappers_64.o
> arch/x86/lib/csum-wrappers_64.o: warning: objtool: csum_and_copy_from_user()+0x29f: call to memset() with UACCESS enabled
> arch/x86/lib/csum-wrappers_64.o: warning: objtool: csum_and_copy_from_user()+0x283: (branch)
> arch/x86/lib/csum-wrappers_64.o: warning: objtool: csum_and_copy_from_user()+0x113: (branch)
> arch/x86/lib/csum-wrappers_64.o: warning: objtool: .altinstr_replacement+0xffffffffffffffff: (branch)
> arch/x86/lib/csum-wrappers_64.o: warning: objtool: csum_and_copy_from_user()+0xea: (alt)
> arch/x86/lib/csum-wrappers_64.o: warning: objtool: .altinstr_replacement+0xffffffffffffffff: (branch)
> arch/x86/lib/csum-wrappers_64.o: warning: objtool: csum_and_copy_from_user()+0xe7: (alt)
> arch/x86/lib/csum-wrappers_64.o: warning: objtool: csum_and_copy_from_user()+0xd2: (branch)
> arch/x86/lib/csum-wrappers_64.o: warning: objtool: csum_and_copy_from_user()+0x7e: (branch)
> arch/x86/lib/csum-wrappers_64.o: warning: objtool: csum_and_copy_from_user()+0x43: (branch)
> arch/x86/lib/csum-wrappers_64.o: warning: objtool: csum_and_copy_from_user()+0x0: <=== (sym)
>
> The problem is with the +0x113 branch, which is at 0x1d1.
>
> That looks to be:
>
> if (!likely(user_access_begin(src, len)))
> goto out_err;
>
> Except that the brach profiling stuff confused GCC enough to leak STAC
> into the error path or something.
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().
--
Josh
next prev parent reply other threads:[~2020-05-29 16:05 UTC|newest]
Thread overview: 36+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-14 0:50 incoming Andrew Morton
2020-05-14 0:50 ` [patch 1/7] mm, memcg: fix inconsistent oom event behavior Andrew Morton
2020-05-14 0:50 ` [patch 2/7] epoll: call final ep_events_available() check under the lock Andrew Morton
2020-05-14 0:50 ` [patch 3/7] mm/gup: fix fixup_user_fault() on multiple retries Andrew Morton
2020-05-14 0:50 ` [patch 4/7] userfaultfd: fix remap event with MREMAP_DONTUNMAP Andrew Morton
2020-05-14 0:50 ` [patch 5/7] ipc/util.c: sysvipc_find_ipc() incorrectly updates position index Andrew Morton
2020-05-14 0:50 ` [patch 6/7] kasan: consistently disable debugging features Andrew Morton
2020-05-14 0:50 ` [patch 7/7] kasan: add missing functions declarations to kasan.h Andrew Morton
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 [this message]
2020-05-29 16:12 ` Peter Zijlstra
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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