[PATCH] x86_64: Turn BUG data into valid instruction

This avoids confusing the disassembler. Costs 2 bytes per BUG.

Thanks to Suresh Siddha and Jan Beulich for suggesting suitable instructions.

Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 10 insertions, 3 deletions

diff --git a/include/asm-x86_64/bug.h b/include/asm-x86_64/bug.h
index 3d2a666a5dd5..eed785667289 100644
--- a/include/asm-x86_64/bug.h
+++ b/include/asm-x86_64/bug.h
@@ -8,17 +8,24 @@
  * this frame.
  */
 struct bug_frame {
-       unsigned char ud2[2];
+        unsigned char ud2[2];
+        unsigned char mov;
         /* should use 32bit offset instead, but the assembler doesn't 
            like it */
         char *filename;
+        unsigned char ret;
         unsigned short line;
 } __attribute__((packed));
 
 #ifdef CONFIG_BUG
 #define HAVE_ARCH_BUG
-#define BUG() \
-        asm volatile("ud2 ; .quad %c1 ; .short %c0" :: \
+/* We turn the bug frame into valid instructions to not confuse
+   the disassembler. Thanks to Jan Beulich & Suresh Siddha
+   for nice instruction selection.
+   The magic numbers generate mov $64bitimm,%eax ; ret $offset. */
+#define BUG()                                                           \
+        asm volatile(                                                   \
+        "ud2 ; .byte 0xa3 ; .quad %c1 ; .byte 0xc2 ; .short %c0" ::     \
                      "i"(__LINE__), "i" (__stringify(__FILE__)))
 void out_of_line_bug(void);
 #else