cbmem console: Locate the preram console with a symbol instead of a section.

On non-x86 systems, the location of the preram CBMEM console may not be in a
predictable place relative to other things in the linker script. That makes it
difficult to work with as its own section because the linker will complain if
you try to move backwards as it lays out memory. If the console header is
treated as an actual blob of memory which has to be put in the image, we'd
have to predict where to put it so that it isn't before something with a lower
address or after something with a higher address. Symbols, on the other hand,
can be defined arbitrarily.

Change-Id: I3257b981eee0c15bb997a9f2c55a03494c6ec6f0
Signed-off-by: Gabe Black <gabeblack@google.com>
Reviewed-on: https://chromium-review.googlesource.com/193164
Reviewed-by: Tom Warren <twarren@nvidia.com>
Reviewed-by: Aaron Durbin <adurbin@chromium.org>
Commit-Queue: Gabe Black <gabeblack@chromium.org>
Tested-by: Gabe Black <gabeblack@chromium.org>
(cherry picked from commit a492761c27076bcac080013d509ae4aafd6dc3e3)
Signed-off-by: Isaac Christensen <isaac.christensen@se-eng.com>
Reviewed-on: http://review.coreboot.org/7013
Tested-by: build bot (Jenkins)
Reviewed-by: Ronald G. Minnich <rminnich@gmail.com>

src/arch/arm/include/arch/early_variables.h

@@ -21,7 +21,6 @@
 #define ARCH_EARLY_VARIABLES_H
 
 #define CAR_GLOBAL
-#define CAR_CBMEM
 
 #define CAR_MIGRATE(migrate_fn_)
 static inline void *car_get_var_ptr(void *var) { return var; }

src/arch/x86/include/arch/early_variables.h

@@ -26,10 +26,8 @@ asm(".previous");
 asm(".section .car.cbmem_console,\"w\",@nobits");
 asm(".previous");
 #define CAR_GLOBAL __attribute__((section(".car.global_data")))
-#define CAR_CBMEM __attribute__((section(".car.cbmem_console")))
 #else
 #define CAR_GLOBAL
-#define CAR_CBMEM
 #endif
 
 #if defined(__PRE_RAM__)

src/arch/x86/init/romstage.ld

@@ -55,15 +55,15 @@ SECTIONS
 	.car.data . (NOLOAD) : {
 		_car_data_start = .;
 		*(.car.global_data);
-		/* The cbmem_console section comes last to take advantage of
-		 * a zero-sized array to hold the memconsole contents that
-		 * grows to a bound of CONFIG_CONSOLE_CAR_BUFFER_SIZE. However,
-		 * collisions within the cache-as-ram region cannot be
+		_car_data_end = .;
+		/* The preram cbmem console area comes last to take advantage
+		 * of a zero-sized array to hold the memconsole contents that
+		 * grows to a bound of CONFIG_CONSOLE_PRERAM_BUFFER_SIZE.
+		 * However, collisions within the cache-as-ram region cannot be
 		 * statically checked because the cache-as-ram region usage is
 		 * cpu/chipset dependent. */
-		*(.car.cbmem_console);
-		_car_data_end = .;
+		preram_cbmem_console = .;
 	}
 
-	_bogus = ASSERT((SIZEOF(.car.data) <= CONFIG_DCACHE_RAM_SIZE), "Cache as RAM area is too full");
+	_bogus = ASSERT((SIZEOF(.car.data) + CONFIG_CONSOLE_PRERAM_BUFFER_SIZE <= CONFIG_DCACHE_RAM_SIZE), "Cache as RAM area is too full");
 }