From 3d1e236022cc1426b0834565995ddee2ca231cee Mon Sep 17 00:00:00 2001 From: Josh Poimboeuf Date: Fri, 24 Feb 2017 22:31:02 -0600 Subject: [PATCH] objtool: Prevent GCC from merging annotate_unreachable() MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 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: kbuild test robot Signed-off-by: Josh Poimboeuf Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Fixes: d1091c7fa3d5 ("objtool: Improve detection of BUG() and other dead ends") Link: http://lkml.kernel.org/r/0c14b00baf9f68d1b0221ddb6c88b925181c8be8.1487997036.git.jpoimboe@redhat.com Signed-off-by: Ingo Molnar --- 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 8ea159fc489d..de471346b365 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()