[PATCH] x86-64: reduce x86-64 bug frame by 4 bytes

As mentioned before, the size of the bug frame can be further reduced while
continuing to use instructions to encode the information.
Signed-off-by: Jan Beulich <jbeulich@novell.com>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

arch/x86_64/kernel/traps.c

@@ -321,13 +321,13 @@ void handle_BUG(struct pt_regs *regs)
 	if (__copy_from_user(&f, (struct bug_frame *) regs->rip, 
 			     sizeof(struct bug_frame)))
 		return; 
-	if ((unsigned long)f.filename < __PAGE_OFFSET || 
+	if (f.filename >= 0 ||
 	    f.ud2[0] != 0x0f || f.ud2[1] != 0x0b) 
 		return;
-	if (__get_user(tmp, f.filename))
-		f.filename = "unmapped filename"; 
+	if (__get_user(tmp, (char *)(long)f.filename))
+		f.filename = (int)(long)"unmapped filename";
 	printk("----------- [cut here ] --------- [please bite here ] ---------\n");
-	printk(KERN_ALERT "Kernel BUG at %.50s:%d\n", f.filename, f.line);
+	printk(KERN_ALERT "Kernel BUG at %.50s:%d\n", (char *)(long)f.filename, f.line);
 } 
 
 #ifdef CONFIG_BUG

include/asm-x86_64/bug.h

@@ -9,10 +9,8 @@
  */
 struct bug_frame {
 	unsigned char ud2[2];
-	unsigned char mov;
-	/* should use 32bit offset instead, but the assembler doesn't 
-	   like it */
-	char *filename;
+	unsigned char push;
+	signed int filename;
 	unsigned char ret;
 	unsigned short line;
 } __attribute__((packed));
@@ -25,8 +23,8 @@ struct bug_frame {
    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__)))
+	"ud2 ; pushq $%c1 ; ret $%c0" :: 				\
+		     "i"(__LINE__), "i" (__FILE__))
 void out_of_line_bug(void);
 #else
 static inline void out_of_line_bug(void) { }