Subject: [PATCH] compiler, READ_ONCE: Fix build failure with some older GCC

From: Andrey Ryabinin <[email-masked]>
Date: Thu, 15 Oct 2015 13:19:51 +0300

Some old versions of GCC doesn't handle __alias (or maybe a combination
of 'static __always_inline __alias') right.

GCC creates outline and unused copy of __read_once_size_check()
function in the object file which references memcpy and causes
the build failure:
	arch/x86/entry/vdso/vclock_gettime.o: In function `__read_once_size_check':
	vclock_gettime.c:(.text+0x5f): undefined reference to `memcpy'
	arch/x86/entry/vdso/vgetcpu.o: In function `__read_once_size_check':
	vgetcpu.c:(.text+0x2f): undefined reference to `memcpy'

We could avoid using alias to work around this problem.

Reported-by: Stephen Rothwell <[email-masked]>
Signed-off-by: Andrey Ryabinin <[email-masked]>
---
 include/linux/compiler.h | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/include/linux/compiler.h b/include/linux/compiler.h
index aa2ae4c..3436a4c 100644
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -231,8 +231,11 @@ void __read_once_size_nocheck(const volatile void *p, void *res, int size)
 	__READ_ONCE_SIZE;
 }
 #else
-static __always_inline __alias(__read_once_size_check)
-void __read_once_size_nocheck(const volatile void *p, void *res, int size);
+static __always_inline
+void __read_once_size_nocheck(const volatile void *p, void *res, int size)
+{
+	__READ_ONCE_SIZE;
+}
 #endif
 
 static __always_inline void __write_once_size(volatile void *p, void *res, int size)
-- 
2.4.9