[tip: x86/fpu] x86/fpu: Fully optimize out WARN_ON_FPU()

[tip-bot2 for Eric Biggers]

The following commit has been merged into the x86/fpu branch of tip:

Commit-ID:     ccb7735a1ea22621f21c3133e4f5f3da5fe5f5b7
Gitweb:        https://git.kernel.org/tip/ccb7735a1ea22621f21c3133e4f5f3da5fe5f5b7
Author:        Eric Biggers <ebiggers@xxxxxxxxxx>
AuthorDate:    Mon, 27 Jan 2025 14:45:23 -08:00
Committer:     Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
CommitterDate: Mon, 10 Feb 2025 14:45:59 -08:00

x86/fpu: Fully optimize out WARN_ON_FPU()

Currently WARN_ON_FPU evaluates its argument even if
CONFIG_X86_DEBUG_FPU is disabled, which adds unnecessary instructions to
several functions, for example kernel_fpu_begin().  Fix this by using
BUILD_BUG_ON_INVALID(x) in the no-debug case rather than (void)(x).

Fixes: 83242c515881 ("x86/fpu: Make WARN_ON_FPU() more robust in the !CONFIG_X86_DEBUG_FPU case")
Suggested-by: Sean Christopherson <seanjc@xxxxxxxxxx>
Signed-off-by: Eric Biggers <ebiggers@xxxxxxxxxx>
Signed-off-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Link: https://lore.kernel.org/all/20250127224523.94300-1-ebiggers%40kernel.org
---
 arch/x86/kernel/fpu/internal.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kernel/fpu/internal.h b/arch/x86/kernel/fpu/internal.h
index dbdb31f..975de07 100644
--- a/arch/x86/kernel/fpu/internal.h
+++ b/arch/x86/kernel/fpu/internal.h
@@ -18,7 +18,7 @@ static __always_inline __pure bool use_fxsr(void)
 #ifdef CONFIG_X86_DEBUG_FPU
 # define WARN_ON_FPU(x) WARN_ON_ONCE(x)
 #else
-# define WARN_ON_FPU(x) ({ (void)(x); 0; })
+# define WARN_ON_FPU(x) ({ BUILD_BUG_ON_INVALID(x); 0; })
 #endif
 
 /* Used in init.c */