x86/cpufeature: Guard asm_volatile_goto usage for BPF compilation

Workaround for the sake of BPF compilation which utilizes kernel
headers, but clang does not support ASM GOTO and fails the build.

Fixes: d0266046ad54 ("x86: Remove FAST_FEATURE_TESTS")
Suggested-by: Thomas Gleixner <[e-mail]>
Signed-off-by: Alexei Starovoitov <[e-mail]>
Signed-off-by: Thomas Gleixner <[e-mail]>
Cc: [e-mail]
Cc: [e-mail]
Cc: [e-mail]
Cc: [e-mail]
Cc: [e-mail]
Cc: [e-mail]
Cc: [e-mail]
Cc: [e-mail]
Link: https://lkml.kernel.org/r/[e-mail]

arch/x86/include/asm/cpufeature.h

···
 
 #define setup_force_cpu_bug(bit) setup_force_cpu_cap(bit)
 
+#if defined(__clang__) && !defined(CC_HAVE_ASM_GOTO)
+
+/*
+ * Workaround for the sake of BPF compilation which utilizes kernel
+ * headers, but clang does not support ASM GOTO and fails the build.
+ */
+#ifndef __BPF_TRACING__
+#warning "Compiler lacks ASM_GOTO support. Add -D __BPF_TRACING__ to your compiler arguments"
+#endif
+
+#define static_cpu_has(bit)            boot_cpu_has(bit)
+
+#else
+
 /*
  * Static testing of CPU features.  Used the same as boot_cpu_has().
  * These will statically patch the target code for additional
···
 		boot_cpu_has(bit) :				\
 		_static_cpu_has(bit)				\
 )
+#endif
 
 #define cpu_has_bug(c, bit)		cpu_has(c, (bit))
 #define set_cpu_bug(c, bit)		set_cpu_cap(c, (bit))

samples/bpf/Makefile

···
 $(obj)/%.o: $(src)/%.c
 	$(CLANG) $(NOSTDINC_FLAGS) $(LINUXINCLUDE) $(EXTRA_CFLAGS) -I$(obj) \
 		-I$(srctree)/tools/testing/selftests/bpf/ \
-		-D__KERNEL__ -Wno-unused-value -Wno-pointer-sign \
+		-D__KERNEL__ -D__BPF_TRACING__ -Wno-unused-value -Wno-pointer-sign \
 		-D__TARGET_ARCH_$(ARCH) -Wno-compare-distinct-pointer-types \
 		-Wno-gnu-variable-sized-type-not-at-end \
 		-Wno-address-of-packed-member -Wno-tautological-compare \