arm64: Bump exception stack size to 2KB

To avoid trampling over interesting exception artifacts on the real
stack, our arm64 systems switch to a separate exception stack when
entering an exception handler. We don't want that to use up too much
SRAM so we just set it to 512 bytes. I mean it just prints a bunch of
registers, how much stack could it need, right?

Quite a bit it turns out. The whole vtxprintf() call stack goes pretty
deep, and aarch64 generally seems to be very generous with stack space.
Just the varargs handling seems to require 128 bytes for some reason,
and the other stuff adds up too. In the end the current implementation
takes 1008 bytes, so bump the exception stack size to 2K to make sure it
fits.

Change-Id: I910be4c5f6b29fae35eb53929c733a1bd4585377
Signed-off-by: Julius Werner <jwerner@chromium.org>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/37464
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Hung-Te Lin <hungte@chromium.org>

payloads/libpayload/arch/arm64/exception.c

@@ -31,7 +31,7 @@
 #include <libpayload.h>
 #include <stdint.h>
 
-u64 exception_stack[0x200] __attribute__((aligned(16)));
+u64 exception_stack[2*KiB] __attribute__((aligned(16)));
 u64 *exception_stack_end = exception_stack + ARRAY_SIZE(exception_stack);
 extern unsigned int test_exc;
 

src/arch/arm64/armv8/exception.c

@@ -36,7 +36,7 @@
 #include <console/console.h>
 #include <arch/lib_helpers.h>
 
-uint8_t exception_stack[0x200] __attribute__((aligned(16)));
+uint8_t exception_stack[2*KiB] __attribute__((aligned(16)));
 
 static const char *exception_names[NUM_EXC_VIDS] = {
 	[EXC_VID_CUR_SP_EL0_SYNC] = "_sync_sp_el0",