arch/x86: allow global .bss objects without CAR_GLOBAL

For platforms utilizing CONFIG_NO_CAR_GLOBAL_MIGRATION there's
no need to automatically migrate globals. Because of this it's
possible to automatically allow for uninitialized global variables
which reside in the .bss section without needing to decorate those
objects with CAR_GLOBAL.

Change-Id: Icae806fecd936ed2ebf0c13d30ffa07c77a95150
Signed-off-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-on: https://review.coreboot.org/29359
Reviewed-by: Furquan Shaikh <furquan@google.com>
Reviewed-by: Nico Huber <nico.h@gmx.de>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
diff --git a/src/arch/x86/car.ld b/src/arch/x86/car.ld
index 7122776..33fb5c9 100644
--- a/src/arch/x86/car.ld
+++ b/src/arch/x86/car.ld
@@ -71,7 +71,17 @@
 	 * cbmem console. This is useful for clearing this area on a per-stage
 	 * basis when more than one stage uses cache-as-ram for CAR_GLOBALs. */
 	_car_global_start = .;
+#if IS_ENABLED(CONFIG_NO_CAR_GLOBAL_MIGRATION)
+	/* Allow global unitialized variables when CAR_GLOBALs are not used. */
+	*(.bss)
+	*(.bss.*)
+	*(.sbss)
+	*(.sbss.*)
+#else
+	/* .car.global_data objects only around when
+	 * !CONFIG_NO_CAR_GLOBAL_MIGRATION is employed. */
 	*(.car.global_data);
+#endif
 	. = ALIGN(ARCH_POINTER_ALIGN_SIZE);
 	_car_global_end = .;
 	_car_relocatable_data_end = .;
@@ -88,10 +98,15 @@
 .illegal_globals . : {
 	*(EXCLUDE_FILE ("*/libagesa.*.a:" "*/romstage*/buildOpts.o" "*/romstage*/agesawrapper.o" "*/vendorcode/amd/agesa/*" "*/vendorcode/amd/cimx/*") .data)
 		*(EXCLUDE_FILE ("*/libagesa.*.a:" "*/romstage*/buildOpts.o" "*/romstage*/agesawrapper.o" "*/vendorcode/amd/agesa/*" "*/vendorcode/amd/cimx/*") .data.*)
+#if !IS_ENABLED(CONFIG_NO_CAR_GLOBAL_MIGRATION)
 	*(.bss)
 	*(.bss.*)
 	*(.sbss)
 	*(.sbss.*)
+#else
+	/* In case something sneaks through when it shouldn't. */
+	*(.car.global_data);
+#endif
 }
 
 _bogus = ASSERT((CONFIG_DCACHE_RAM_SIZE == 0) || (SIZEOF(.car.data) <= CONFIG_DCACHE_RAM_SIZE), "Cache as RAM area is too full");
diff --git a/src/arch/x86/include/arch/early_variables.h b/src/arch/x86/include/arch/early_variables.h
index 1b6810d..d215e47 100644
--- a/src/arch/x86/include/arch/early_variables.h
+++ b/src/arch/x86/include/arch/early_variables.h
@@ -20,7 +20,7 @@
 #include <stdlib.h>
 #include <rules.h>
 
-#if ENV_CACHE_AS_RAM
+#if ENV_CACHE_AS_RAM && !IS_ENABLED(CONFIG_NO_CAR_GLOBAL_MIGRATION)
 asm(".section .car.global_data,\"w\",@nobits");
 asm(".previous");
 #ifdef __clang__
@@ -34,7 +34,7 @@
  * accessed unconditionally because cbmem is never initialized until romstage
  * when dram comes up.
  */
-#if ENV_VERSTAGE || ENV_BOOTBLOCK || IS_ENABLED(CONFIG_NO_CAR_GLOBAL_MIGRATION)
+#if ENV_VERSTAGE || ENV_BOOTBLOCK
 static inline void *car_get_var_ptr(void *var)
 {
 	return var;