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 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 index 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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