x86/asm: Add ASM_UNREACHABLE

This creates an unreachable annotation in asm for CONFIG_STACK_VALIDATION=y.
While here, adjust earlier uses of \t\n into \n\t.

Suggested-by: Josh Poimboeuf <[email protected]>
Signed-off-by: Kees Cook <[email protected]>
Cc: Alexey Dobriyan <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: Arnd Bergmann <[email protected]>
Cc: Christoph Hellwig <[email protected]>
Cc: David S. Miller <[email protected]>
Cc: Davidlohr Bueso <[email protected]>
Cc: Elena Reshetova <[email protected]>
Cc: Eric Biggers <[email protected]>
Cc: Eric W. Biederman <[email protected]>
Cc: Greg KH <[email protected]>
Cc: Hans Liljestrand <[email protected]>
Cc: James Bottomley <[email protected]>
Cc: Jann Horn <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Manfred Spraul <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Rik van Riel <[email protected]>
Cc: Serge E. Hallyn <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: linux-arch <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>

Author: kees

include/linux/compiler-gcc.h

@@ -203,11 +203,16 @@
 
 #ifdef CONFIG_STACK_VALIDATION
 #define annotate_unreachable() ({					\
-	asm("%c0:\t\n"							\
-	    ".pushsection .discard.unreachable\t\n"			\
-	    ".long %c0b - .\t\n"					\
-	    ".popsection\t\n" : : "i" (__LINE__));			\
+	asm("%c0:\n\t"							\
+	    ".pushsection .discard.unreachable\n\t"			\
+	    ".long %c0b - .\n\t"					\
+	    ".popsection\n\t" : : "i" (__LINE__));			\
 })
+#define ASM_UNREACHABLE							\
+	"999:\n\t"							\
+	".pushsection .discard.unreachable\n\t"				\
+	".long 999b - .\n\t"						\
+	".popsection\n\t"
 #else
 #define annotate_unreachable()
 #endif

include/linux/compiler.h

@@ -185,6 +185,9 @@ void ftrace_likely_update(struct ftrace_likely_data *f, int val,
 #endif
 
 /* Unreachable code */
+#ifndef ASM_UNREACHABLE
+# define ASM_UNREACHABLE
+#endif
 #ifndef unreachable
 # define unreachable() do { } while (1)
 #endif