From: Josh Poimboeuf <jpoimboe@redhat.com>
To: x86@kernel.org
Cc: Andy Lutomirski <luto@kernel.org>,
kbuild-all@01.org, linux-kernel@vger.kernel.org,
tipbuild@zytor.com, Ingo Molnar <mingo@kernel.org>,
Borislav Petkov <bp@suse.de>,
kbuild test robot <fengguang.wu@intel.com>
Subject: [PATCH] objtool: Prevent GCC from merging annotate_unreachable(), take 2
Date: Fri, 3 Nov 2017 17:19:41 -0500 [thread overview]
Message-ID: <20171103221941.cajpwszir7ujxyc4@treble> (raw)
In-Reply-To: <20171103155027.yhypc4tydthaifss@treble>
This fixes the following warning with GCC 4.6:
mm/migrate.o: warning: objtool: migrate_misplaced_transhuge_page()+0x71: unreachable instruction
The problem is that the compiler merged identical annotate_unreachable()
inline asm blocks, resulting in a missing 'unreachable' annotation.
This problem happened before, and was partially fixed with:
3d1e236022cc ("objtool: Prevent GCC from merging annotate_unreachable()")
That commit tried to ensure that each instance of the
annotate_unreachable() inline asm statement has a unique label. It used
the __LINE__ macro to generate the label number. However, even the line
number isn't necessarily unique when used in an inline function with
multiple callers (in this case, __alloc_pages_node()'s use of
VM_BUG_ON).
Reported-by: kbuild test robot <fengguang.wu@intel.com>
Fixes: 3d1e236022cc ("objtool: Prevent GCC from merging annotate_unreachable()")
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
---
include/linux/compiler.h | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/include/linux/compiler.h b/include/linux/compiler.h
index e95a2631e545..e9fe95b138cf 100644
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -190,13 +190,13 @@ void ftrace_likely_update(struct ftrace_likely_data *f, int val,
asm("%c0:\n\t" \
".pushsection .discard.reachable\n\t" \
".long %c0b - .\n\t" \
- ".popsection\n\t" : : "i" (__LINE__)); \
+ ".popsection\n\t" : : "i" (__COUNTER__)); \
})
#define annotate_unreachable() ({ \
asm("%c0:\n\t" \
".pushsection .discard.unreachable\n\t" \
".long %c0b - .\n\t" \
- ".popsection\n\t" : : "i" (__LINE__)); \
+ ".popsection\n\t" : : "i" (__COUNTER__)); \
})
#define ASM_UNREACHABLE \
"999:\n\t" \
--
2.13.6
next prev parent reply other threads:[~2017-11-03 22:19 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-11-03 3:36 [tip:x86/asm 24/32] mm/migrate.o: warning: objtool: migrate_misplaced_transhuge_page()+0x71: unreachable instruction kbuild test robot
2017-11-03 15:50 ` Josh Poimboeuf
2017-11-03 22:19 ` Josh Poimboeuf [this message]
2017-11-04 22:31 ` [tip:core/urgent] objtool: Prevent GCC from merging annotate_unreachable(), take 2 tip-bot for Josh Poimboeuf
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