kasan, powerpc: don't rename memintrinsics if compiler adds prefixes

With appropriate compiler support [1], KASAN builds use __asan prefixed
meminstrinsics, and KASAN no longer overrides memcpy/memset/memmove.

If compiler support is detected (CC_HAS_KASAN_MEMINTRINSIC_PREFIX), define
memintrinsics normally (do not prefix '__').

On powerpc, KASAN is the only user of __mem functions, which are used to
define instrumented memintrinsics. Alias the normal versions for KASAN to
use in its implementation.

Link: https://lore.kernel.org/all/[e-mail]/ [1]
Link: https://lore.kernel.org/oe-kbuild-all/[e-mail]/
Link: https://lkml.kernel.org/r/[e-mail]
Signed-off-by: Marco Elver <[e-mail]>
Reported-by: kernel test robot <[e-mail]>
Acked-by: Michael Ellerman <[e-mail]> [powerpc]
Cc: Alexander Potapenko <[e-mail]>
Cc: Andrey Konovalov <[e-mail]>
Cc: Andrey Ryabinin <[e-mail]>
Cc: Christophe Leroy <[e-mail]>
Cc: Daniel Axtens <[e-mail]>
Cc: Dmitry Vyukov <[e-mail]>
Cc: Liam R. Howlett <[e-mail]>
Cc: Nicholas Piggin <[e-mail]>
Cc: Vincenzo Frascino <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>

arch/powerpc/include/asm/kasan.h

···
 #ifndef __ASM_KASAN_H
 #define __ASM_KASAN_H
 
-#ifdef CONFIG_KASAN
+#if defined(CONFIG_KASAN) && !defined(CONFIG_CC_HAS_KASAN_MEMINTRINSIC_PREFIX)
 #define _GLOBAL_KASAN(fn)	_GLOBAL(__##fn)
 #define _GLOBAL_TOC_KASAN(fn)	_GLOBAL_TOC(__##fn)
 #define EXPORT_SYMBOL_KASAN(fn)	EXPORT_SYMBOL(__##fn)

arch/powerpc/include/asm/string.h

···
 extern void * memchr(const void *,int,__kernel_size_t);
 void memcpy_flushcache(void *dest, const void *src, size_t size);
 
+#ifdef CONFIG_KASAN
+/* __mem variants are used by KASAN to implement instrumented meminstrinsics. */
+#ifdef CONFIG_CC_HAS_KASAN_MEMINTRINSIC_PREFIX
+#define __memset memset
+#define __memcpy memcpy
+#define __memmove memmove
+#else /* CONFIG_CC_HAS_KASAN_MEMINTRINSIC_PREFIX */
 void *__memset(void *s, int c, __kernel_size_t count);
 void *__memcpy(void *to, const void *from, __kernel_size_t n);
 void *__memmove(void *to, const void *from, __kernel_size_t n);
-
-#if defined(CONFIG_KASAN) && !defined(__SANITIZE_ADDRESS__)
+#ifndef __SANITIZE_ADDRESS__
 /*
  * For files that are not instrumented (e.g. mm/slub.c) we
  * should use not instrumented version of mem* functions.
···
 #ifndef __NO_FORTIFY
 #define __NO_FORTIFY /* FORTIFY_SOURCE uses __builtin_memcpy, etc. */
 #endif
-
-#endif
+#endif /* !__SANITIZE_ADDRESS__ */
+#endif /* CONFIG_CC_HAS_KASAN_MEMINTRINSIC_PREFIX */
+#endif /* CONFIG_KASAN */
 
 #ifdef CONFIG_PPC64
 #ifndef CONFIG_KASAN

arch/powerpc/kernel/prom_init_check.sh

···
 # If you really need to reference something from prom_init.o add
 # it to the list below:
 
-grep "^CONFIG_KASAN=y$" ${KCONFIG_CONFIG} >/dev/null
-if [ $? -eq 0 ]
+has_renamed_memintrinsics()
+{
+	grep -q "^CONFIG_KASAN=y$" ${KCONFIG_CONFIG} && \
+		! grep -q "^CONFIG_CC_HAS_KASAN_MEMINTRINSIC_PREFIX=y" ${KCONFIG_CONFIG}
+}
+
+if has_renamed_memintrinsics
 then
 	MEM_FUNCS="__memcpy __memset"
 else