From ca8b5d97d6bfd2d24cec053bbbe35cf356bec4e3 Mon Sep 17 00:00:00 2001 From: Nicolas Pitre Date: Fri, 25 Aug 2017 00:54:18 -0400 Subject: ARM: XIP kernel: store .data compressed in ROM The .data segment stored in ROM is only copied to RAM once at boot time and never referenced afterwards. This is arguably a suboptimal usage of ROM resources. This patch allows for compressing the .data segment before storing it into ROM and decompressing it to RAM rather than simply copying it, saving on precious ROM space. Because global data is not available yet (obviously) we must allocate decompressor workspace memory on the stack. The .bss area is used as a stack area for that purpose before it is cleared. The required stack frame is 9568 bytes for __inflate_kernel_data() alone, so make sure the .bss is large enough to cope with that plus extra room for called functions or fail the build. Those numbers were picked arbitrarily based on the above 9568 byte stack frame: 10240 (2.5 * PAGE_SIZE): used to override -Wframe-larger-than whose default value is 1024. 12288 (3 * PAGE_SIZE): minimum .bss size to contain the stack. Signed-off-by: Nicolas Pitre Reviewed-by: Ard Biesheuvel Tested-by: Chris Brandt --- arch/arm/kernel/Makefile | 5 +++++ 1 file changed, 5 insertions(+) (limited to 'arch/arm/kernel/Makefile') diff --git a/arch/arm/kernel/Makefile b/arch/arm/kernel/Makefile index ad325a8c7e1e..52f437997cc6 100644 --- a/arch/arm/kernel/Makefile +++ b/arch/arm/kernel/Makefile @@ -87,6 +87,11 @@ head-y := head$(MMUEXT).o obj-$(CONFIG_DEBUG_LL) += debug.o obj-$(CONFIG_EARLY_PRINTK) += early_printk.o +# This is executed very early using a temporary stack when no memory allocator +# nor global data is available. Everything has to be allocated on the stack. +CFLAGS_head-inflate-data.o := $(call cc-option,-Wframe-larger-than=10240) +obj-$(CONFIG_XIP_DEFLATED_DATA) += head-inflate-data.o + obj-$(CONFIG_ARM_VIRT_EXT) += hyp-stub.o AFLAGS_hyp-stub.o :=-Wa,-march=armv7-a ifeq ($(CONFIG_ARM_PSCI),y) -- cgit