armv8: make SPL exception vectors optional

Even though the exception vector table is a fundamental part of the ARM
architecture, U-Boot mostly does not make real use of it, except when
crash dumping. But having it in takes up quite some space, partly due to
the architectural alignment requirement of 2KB. Since we don't take special
care of that, the compiler adds a more or less random amount of padding
space, which increases the image size quite a bit, especially for the SPL.

On a typical Allwinner build this is around 1.5KB of padding, plus 1KB
for the vector table (mostly padding space again), then some extra code
to do the actual handling. This amounts to almost 10% of the maximum image
size, which is quite a lot for a pure debugging feature.

Add a Kconfig symbol to allow the exception vector table to be left out
of the build for the SPL.
For now this is "default y" for everyone, but specific defconfigs,
platforms or .config files can opt out here at will, to mitigate the code
size pressure we see for some SPLs.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>

1 files changed, 11 insertions, 0 deletions

diff --git a/arch/arm/cpu/armv8/Kconfig b/arch/arm/cpu/armv8/Kconfig
index 741e15c..c8bebab 100644
--- a/arch/arm/cpu/armv8/Kconfig
+++ b/arch/arm/cpu/armv8/Kconfig
@@ -1,5 +1,16 @@
 if ARM64
 
+config ARMV8_SPL_EXCEPTION_VECTORS
+	bool "Install crash dump exception vectors"
+	depends on SPL
+	default y
+	help
+	  The default exception vector table is only used for the crash
+	  dump, but still takes quite a lot of space in the image size.
+
+	  Say N here if you are running out of code space in the image
+	  and want to save some space at the cost of less debugging info.
+
 config ARMV8_MULTIENTRY
         bool "Enable multiple CPUs to enter into U-Boot"