On Wed, Jul 25, 2018 at 12:57:01AM +0100, Andre Przywara wrote:
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
arch/arm/cpu/armv8/Kconfig | 11 +++++++++++ arch/arm/cpu/armv8/Makefile | 4 ++++ arch/arm/cpu/armv8/start.S | 19 +++++++++++++++---- 3 files changed, 30 insertions(+), 4 deletions(-)
diff --git a/arch/arm/cpu/armv8/Kconfig b/arch/arm/cpu/armv8/Kconfig index 22d2f29548..bd1e759c37 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 crashdump, 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 imageand want to save some space at the cost of less debugging info.config ARMV8_MULTIENTRY bool "Enable multiple CPUs to enter into U-Boot"
diff --git a/arch/arm/cpu/armv8/Makefile b/arch/arm/cpu/armv8/Makefile index d1d4ffecfd..52c8daa049 100644 --- a/arch/arm/cpu/armv8/Makefile +++ b/arch/arm/cpu/armv8/Makefile @@ -10,7 +10,11 @@ ifndef CONFIG_$(SPL_TPL_)TIMER obj-$(CONFIG_SYS_ARCH_TIMER) += generic_timer.o endif obj-y += cache_v8.o +ifdef CONFIG_SPL_BUILD +obj-$(CONFIG_ARMV8_SPL_EXCEPTION_VECTORS) += exceptions.o +else obj-y += exceptions.o +endif
I _think_ we can make the code parts of this read better (and make use of CONFIG_IS_ENABLED() if we add CONFIG_ARMV8_EXCEPTION_VECTORS and don't allow it to be unselected (ie no text on the bool line).