Commit d15dc68c authored by Paul Burton's avatar Paul Burton Committed by Ralf Baechle
Browse files

MIPS: cmpxchg: Error out on unsupported xchg() calls 



xchg() has up until now simply returned the x parameter in cases where
it is called with a pointer to a value of an unsupported size. This will
often cause the calling code to hit a failure path, presuming that the
value of x differs from the content of the memory pointed at by ptr, but
we can do better by producing a compile-time or link-time error such
that unsupported calls to xchg() are detectable earlier than runtime.

This patch does this in the same was as is already done for cmpxchg(),
using a call to a missing function annotated with __compiletime_error().

Signed-off-by: default avatarPaul Burton <paul.burton@imgtec.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/16351/


Signed-off-by: default avatarRalf Baechle <ralf@linux-mips.org>
parent 77299db8

arch/mips/include/asm/cmpxchg.h

+17 −15
Original line number Diff line number Diff line
@@ -24,6 +24,21 @@ 
# define __scbeqz "beqz"

#endif



/*

 * These functions doesn't exist, so if they are called you'll either:

 *

 * - Get an error at compile-time due to __compiletime_error, if supported by

 *   your compiler.

 *

 * or:

 *

 * - Get an error at link-time due to the call to the missing function.

 */

extern void __cmpxchg_called_with_bad_pointer(void)

	__compiletime_error("Bad argument size for cmpxchg");

extern unsigned long __xchg_called_with_bad_pointer(void)

	__compiletime_error("Bad argument size for xchg");



#define __xchg_asm(ld, st, m, val)					\

({									\

	__typeof(*(m)) __ret;						\
@@ -89,9 +104,9 @@ static inline unsigned long __xchg(unsigned long x, volatile void * ptr, int siz 
		return __xchg_u32(ptr, x);

	case 8:

		return __xchg_u64(ptr, x);

	default:

		return __xchg_called_with_bad_pointer();

	}



	return x;

}



#define xchg(ptr, x)							\
@@ -136,19 +151,6 @@ static inline unsigned long __xchg(unsigned long x, volatile void * ptr, int siz 
	__ret;								\

})



/*

 * This function doesn't exist, so if it is called you'll either:

 *

 * - Get an error at compile-time due to __compiletime_error, if supported by

 *   your compiler.

 *

 * or:

 *

 * - Get an error at link-time due to the call to the missing function.

 */

extern void __cmpxchg_called_with_bad_pointer(void)

	__compiletime_error("Bad argument size for cmpxchg");



#define __cmpxchg(ptr, old, new, pre_barrier, post_barrier)		\

({									\

	__typeof__(ptr) __ptr = (ptr);					\

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