From: Andi Kleen <ak@suse.de>
Date: Fri, 29 Jul 2005 04:15:45 +0000 (-0700)
Subject: [PATCH] x86_64: Turn BUG data into valid instruction
X-Git-Url: https://git.stricted.de/?a=commitdiff_plain;h=b6a68a16dc15c65fe76acb7502a806ae415cd3e4;p=GitHub%2FLineageOS%2FG12%2Fandroid_kernel_amlogic_linux-4.9.git

[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>
---

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