[PATCH v4 3/4] x86/cpuid: fix unbootable VMs by really inlining memcmp() in hypervisor_cpuid_base()

[Mauricio Faria de Oliveira <mfo@xxxxxxxxxx>]

Even with __builtin the compiler may decide to use the out of line function
instead of the inline implementation.

The existing code is broken with gcc-14/15 but not gcc-12/13 (Ubuntu 25.10)
and vmlinux no longer boots with CONFIG_PVH if CONFIG_KASAN_GENERIC is set.

For testing purposes, if the size argument is reduced from 12 to 8 then the
compiler decides to use the inline implementation; that shows results vary.

Switch the builtin to the inline implementation to address it.

Fixes: 416a33c9afce ("x86/cpu: fix unbootable VMs by inlining memcmp() in 
hypervisor_cpuid_base()")
Signed-off-by: Mauricio Faria de Oliveira <mfo@xxxxxxxxxx>
Reviewed-by: Juergen Gross <jgross@xxxxxxxx>
---
 arch/x86/include/asm/cpuid/api.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/cpuid/api.h b/arch/x86/include/asm/cpuid/api.h
index 
82eddfa2347b32b76c2ea9b85f005ca5416ac71f..2d9f3d4d63de6e721f275d9e80d372edbdfedf30
 100644
--- a/arch/x86/include/asm/cpuid/api.h
+++ b/arch/x86/include/asm/cpuid/api.h
@@ -204,7 +204,7 @@ static inline u32 cpuid_base_hypervisor(const char *sig, 
u32 leaves)
                 * from PVH early boot code before instrumentation is set up
                 * and memcmp() itself may be instrumented.
                 */
-               if (!__builtin_memcmp(sig, signature, 12) &&
+               if (!__inline_memcmp(sig, signature, 12) &&
                    (leaves == 0 || ((eax - base) >= leaves)))
                        return base;
        }

-- 
2.51.0