[PATCH 5.15] x86/its: Fix undefined reference to cpu_wants_rethunk_at()

[Pawan Gupta <pawan.kumar.gupta@linux.intel.com>]

Below error was reported in a 32-bit kernel build:

  static_call.c:(.ref.text+0x46): undefined reference to `cpu_wants_rethunk_at'
  make[1]: [Makefile:1234: vmlinux] Error

This is because the definition of cpu_wants_rethunk_at() depends on
CONFIG_STACK_VALIDATION which is only enabled in 64-bit mode.

Define the empty function for CONFIG_STACK_VALIDATION=n, rethunk mitigation
is anyways not supported without it.

Reported-by: Guenter Roeck <linux@roeck-us.net>
Fixes: 5d19a0574b75 ("x86/its: Add support for ITS-safe return thunk")
Signed-off-by: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
Link: https://lore.kernel.org/stable/0f597436-5da6-4319-b918-9f57bde5634a@roeck-us.net/
---
 arch/x86/include/asm/alternative.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/alternative.h b/arch/x86/include/asm/alternative.h
index 1797f80c10de..a5f704dbb4a1 100644
--- a/arch/x86/include/asm/alternative.h
+++ b/arch/x86/include/asm/alternative.h
@@ -98,7 +98,7 @@ static inline u8 *its_static_thunk(int reg)
 }
 #endif
 
-#ifdef CONFIG_RETHUNK
+#if defined(CONFIG_RETHUNK) && defined(CONFIG_STACK_VALIDATION)
 extern bool cpu_wants_rethunk(void);
 extern bool cpu_wants_rethunk_at(void *addr);
 #else
-- 
2.34.1