objtool: Prevent GCC from merging annotate_unreachable(), take 2
authorJosh Poimboeuf <jpoimboe@redhat.com>
Fri, 3 Nov 2017 22:19:41 +0000 (17:19 -0500)
committerIngo Molnar <mingo@kernel.org>
Sat, 4 Nov 2017 14:03:39 +0000 (15:03 +0100)
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>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@suse.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: kbuild-all@01.org
Cc: tipbuild@zytor.com
Fixes: 3d1e236022cc ("objtool: Prevent GCC from merging annotate_unreachable()")
Link: http://lkml.kernel.org/r/20171103221941.cajpwszir7ujxyc4@treble
Signed-off-by: Ingo Molnar <mingo@kernel.org>
include/linux/compiler.h

index fd8697aa4f7362a63d2f75f958e89a383977a906..202710420d6deba1bba8107616359ae069ffd5e7 100644 (file)
@@ -191,13 +191,13 @@ void ftrace_likely_update(struct ftrace_likely_data *f, int val,
        asm("%c0:\n\t"                                                  \
            ".pushsection .discard.reachable\n\t"                       \
            ".long %c0b - .\n\t"                                        \
        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"                                        \
 })
 #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"                                                      \
 })
 #define ASM_UNREACHABLE                                                        \
        "999:\n\t"                                                      \