cpu/x86/smm: Fix explicit 'addr32' usage in clang builds

The addr32 prefix is required by binutils, because even when
given an explicit address which is greater than 64KiB, it will
throw a warning about truncation, and stupidly emit the opcode
with a 16-bit addressing mode and the wrong address.

However, in the case of LLVM, this doesn't happen, and is happy
to just use 32-bit addressing whenever it may require it. This
means that LLVM never really needs an explicit addr32 prefix to
use 32-bit addressing in 16-bit mode.

Change-Id: Ia160d3f7da6653ea24c8229dc26f265e5f15aabb
Also-by: Damien Zammit <damien@zamaudio.com>
Signed-off-by: Damien Zammit <damien@zamaudio.com>
Reviewed-on: https://review.coreboot.org/21219
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>

src/cpu/x86/smm/smmrelocate.S

@@ -36,6 +36,9 @@
 #error "Southbridge needs SMM handler support."
 #endif
 
+// ADDR32() macro
+#include <compiler.h>
+
 #if IS_ENABLED(CONFIG_SMM_TSEG)
 #error "Don't use this file with TSEG."
 
@@ -112,7 +115,7 @@ smm_relocation_start:
 	 */
 
 	mov $0x38000 + 0x7efc, %ebx
-	addr32 mov (%ebx), %al
+	ADDR32(mov) (%ebx), %al
 	cmp $0x64, %al
 	je 1f
 
@@ -124,7 +127,7 @@ smm_relocation_start:
 smm_relocate:
 	/* Get this CPU's LAPIC ID */
 	movl $LAPIC_ID, %esi
-	addr32 movl (%esi), %ecx
+	ADDR32(movl) (%esi), %ecx
 	shr  $24, %ecx
 
 	/* calculate offset by multiplying the
@@ -136,7 +139,7 @@ smm_relocate:
 	movl $0xa0000, %eax
 	subl %edx, %eax	/* subtract offset, see above */
 
-	addr32 movl %eax, (%ebx)
+	ADDR32(movl) %eax, (%ebx)
 
 	/* The next section of code is potentially southbridge specific */
 

src/include/compiler.h

@@ -26,4 +26,10 @@
 #define __always_unused __attribute__((unused))
 #define __must_check __attribute__((warn_unused_result))
 
+#if IS_ENABLED(CONFIG_COMPILER_LLVM_CLANG)
+#define ADDR32(opcode) opcode
+#else
+#define ADDR32(opcode) addr32 opcode
+#endif
+
 #endif