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.
Fixes: d1091c7fa3d5 ("objtool: Improve detection of BUG() and other dead ends")
Reported-by: kbuild test robot <fengguang...@intel.com>
Cc: Peter Zijlstra <pet...@infradead.org>
Signed-off-by: Josh Poimboeuf <jpoim...@redhat.com>
---
include/linux/compiler-gcc.h | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/include/linux/compiler-gcc.h b/include/linux/compiler-gcc.h
index 8ea159f..de47134 100644
--- a/include/linux/compiler-gcc.h
+++ b/include/linux/compiler-gcc.h
@@ -197,10 +197,10 @@
#ifdef CONFIG_STACK_VALIDATION
#define annotate_unreachable() ({ \
- asm("1:\t\n" \
+ asm("%c0:\t\n" \
".pushsection __unreachable, \"a\"\t\n" \
- ".long 1b\t\n" \
- ".popsection\t\n"); \
+ ".long %c0b\t\n" \
+ ".popsection\t\n" : : "i" (__LINE__)); \
})
#else
#define annotate_unreachable()
--
2.7.4
