x86: provide stage_exit() like arm

The arm architectures have a stage_exit() function
which takes a void * pointer as an entry point. Provide
the same API for x86. This can make the booting paths
less architecture-specific.

Change-Id: I4ecfbf32f38f2e3817381b63e1f97e92654c5f97
Signed-off-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-on: http://review.coreboot.org/5086
Tested-by: build bot (Jenkins)
Reviewed-by: Patrick Georgi <patrick@georgi-clan.de>

src/arch/x86/include/arch/stages.h

@@ -24,4 +24,12 @@
 
 void asmlinkage copy_and_run(void);
 void jmp_to_elf_entry(void *entry, unsigned long buffer, unsigned long size);
+
+static inline void stage_exit(void *entry)
+{
+	__asm__ volatile (
+		"jmp  *%%edi\n"
+		:: "D"(entry)
+	);
+}
 #endif

src/arch/x86/lib/cbfs_and_run.c

@@ -34,10 +34,7 @@ static void cbfs_and_run_core(const char *filename)
 
 	timestamp_add_now(TS_END_COPYRAM);
 	print_debug("Jumping to image.\n");
-	__asm__ volatile (
-		"jmp  *%%edi\n"
-		:: "D"(dst)
-	);
+	stage_exit(dst);
 }
 
 void asmlinkage copy_and_run(void)

src/vendorcode/google/chromeos/vboot_loader.c

@@ -17,6 +17,7 @@
  * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301 USA
  */
 
+#include <arch/stages.h>
 #include <stdint.h>
 #include <stddef.h>
 #include <cbfs.h>
@@ -180,11 +181,7 @@ static void vboot_load_ramstage(struct vboot_handoff *vboot_handoff,
 
 	timestamp_add_now(TS_END_COPYRAM);
 
-	__asm__ volatile (
-		"movl $0, %%ebp\n"
-		"jmp  *%%edi\n"
-		:: "D"(rmod_load.entry)
-	);
+	stage_exit(rmod_load.entry);
 }
 
 void vboot_verify_firmware(struct romstage_handoff *handoff)