Commit 3d1e2360 authored by Josh Poimboeuf's avatar Josh Poimboeuf Committed by Ingo Molnar

objtool: Prevent GCC from merging annotate_unreachable()

0-day bot reported some new objtool warnings which were caused by the
new annotate_unreachable() macro:

  fs/afs/flock.o: warning: objtool: afs_do_unlk()+0x0: duplicate frame pointer save
  fs/afs/flock.o: warning: objtool: afs_do_unlk()+0x0: frame pointer state mismatch
  fs/btrfs/delayed-inode.o: warning: objtool: btrfs_delete_delayed_dir_index()+0x0: duplicate frame pointer save
  fs/btrfs/delayed-inode.o: warning: objtool: btrfs_delete_delayed_dir_index()+0x0: frame pointer state mismatch
  fs/dlm/lock.o: warning: objtool: _grant_lock()+0x0: duplicate frame pointer save
  fs/dlm/lock.o: warning: objtool: _grant_lock()+0x0: frame pointer state mismatch
  fs/ocfs2/alloc.o: warning: objtool: ocfs2_mv_path()+0x0: duplicate frame pointer save
  fs/ocfs2/alloc.o: warning: objtool: ocfs2_mv_path()+0x0: frame pointer state mismatch

It turns out that, for older versions of GCC, if a function has multiple
BUG() incantations, GCC will sometimes merge the corresponding
annotate_unreachable() inline asm statements into a single block.  That
has the undesirable effect of removing one of the entries in the
__unreachable section, confusing objtool greatly.

A workaround for this issue is to ensure that each instance of the
inline asm statement uses a different label, so that GCC sees the
statements are unique and leaves them alone.  The inline asm ‘%=’ token
could be used for that, but unfortunately older versions of GCC don't
support it.  So I implemented a poor man's version of it with the
__LINE__ macro.
Reported-by: default avatarkbuild test robot <fengguang.wu@intel.com>
Signed-off-by: default avatarJosh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Fixes: d1091c7f ("objtool: Improve detection of BUG() and other dead ends")
Link: http://lkml.kernel.org/r/0c14b00baf9f68d1b0221ddb6c88b925181c8be8.1487997036.git.jpoimboe@redhat.comSigned-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent d1091c7f
...@@ -197,10 +197,10 @@ ...@@ -197,10 +197,10 @@
#ifdef CONFIG_STACK_VALIDATION #ifdef CONFIG_STACK_VALIDATION
#define annotate_unreachable() ({ \ #define annotate_unreachable() ({ \
asm("1:\t\n" \ asm("%c0:\t\n" \
".pushsection __unreachable, \"a\"\t\n" \ ".pushsection __unreachable, \"a\"\t\n" \
".long 1b\t\n" \ ".long %c0b\t\n" \
".popsection\t\n"); \ ".popsection\t\n" : : "i" (__LINE__)); \
}) })
#else #else
#define annotate_unreachable() #define annotate_unreachable()
......
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