Re: [PATCH] arch/powerpc: use BUILD_BUG() when detect unfit {cmp}xchg, size

On Tue, 2016-02-23 at 17:15 +0800, Boqun Feng wrote:

On Tue, Feb 23, 2016 at 04:45:16PM +0800, Pan Xinhui wrote:

quoted

From: pan xinhui <redacted>

diff --git a/arch/powerpc/include/asm/cmpxchg.h b/arch/powerpc/include/asm/cmpxchg.h
index d1a8d93..20c0a30 100644
--- a/arch/powerpc/include/asm/cmpxchg.h
+++ b/arch/powerpc/include/asm/cmpxchg.h

@@ -92,12 +93,6 @@ __xchg_u64_local(volatile void *p, unsigned long val)
 }
 #endif
 
-/*
- * This function doesn't exist, so you'll get a linker error
- * if something tries to do an invalid xchg().
- */
-extern void __xchg_called_with_bad_pointer(void);
-
 static __always_inline unsigned long
 __xchg(volatile void *ptr, unsigned long x, unsigned int size)
 {

@@ -109,7 +104,7 @@ __xchg(volatile void *ptr, unsigned long x, unsigned int size)
 		return __xchg_u64(ptr, x);
 #endif
 	}
-	__xchg_called_with_bad_pointer();
+	BUILD_BUG();

Maybe we can use BUILD_BUG_ON_MSG(1, "Unsupported size for xchg"), which
could provide more information.

Yes I would prefer there was a message. Please send a v2.

cheers