Commit ca8b5d97 authored by Nicolas Pitre's avatar Nicolas Pitre
Browse files

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: default avatarNicolas Pitre <nico@linaro.org>
Reviewed-by: default avatarArd Biesheuvel <ard.biesheuvel@linaro.org>
Tested-by: default avatarChris Brandt <Chris.Brandt@renesas.com>
parent 0d302c71

arch/arm/Kconfig

+11 −0
Original line number Diff line number Diff line
@@ -2005,6 +2005,17 @@ config XIP_PHYS_ADDR 
	  be linked for and stored to.  This address is dependent on your

	  own flash usage.



config XIP_DEFLATED_DATA

	bool "Store kernel .data section compressed in ROM"

	depends on XIP_KERNEL

	select ZLIB_INFLATE

	help

	  Before the kernel is actually executed, its .data section has to be

	  copied to RAM from ROM. This option allows for storing that data

	  in compressed form and decompressed to RAM rather than merely being

	  copied, saving some precious ROM space. A possible drawback is a

	  slightly longer boot delay.



config KEXEC

	bool "Kexec system call (EXPERIMENTAL)"

	depends on (!SMP || PM_SLEEP_SMP)

arch/arm/boot/Makefile

+12 −1
Original line number Diff line number Diff line
@@ -31,8 +31,19 @@ targets := Image zImage xipImage bootpImage uImage 


ifeq ($(CONFIG_XIP_KERNEL),y)



cmd_deflate_xip_data = $(CONFIG_SHELL) -c \

	'$(srctree)/$(src)/deflate_xip_data.sh $< $@ || { rm -f $@; false; }'



ifeq ($(CONFIG_XIP_DEFLATED_DATA),y)

quiet_cmd_mkxip = XIPZ    $@

cmd_mkxip = $(cmd_objcopy) && $(cmd_deflate_xip_data)

else

quiet_cmd_mkxip = $(quiet_cmd_objcopy)

cmd_mkxip = $(cmd_objcopy)

endif



$(obj)/xipImage: vmlinux FORCE

	$(call if_changed,objcopy)

	$(call if_changed,mkxip)

	@$(kecho) '  Physical Address of xipImage: $(CONFIG_XIP_PHYS_ADDR)'



$(obj)/Image $(obj)/zImage: FORCE

arch/arm/boot/deflate_xip_data.sh

0 → 100755
+64 −0
Original line number Diff line number Diff line 
#!/bin/sh



# XIP kernel .data segment compressor

#

# Created by:	Nicolas Pitre, August 2017

# Copyright:	(C) 2017  Linaro Limited

#

# This program is free software; you can redistribute it and/or modify

# it under the terms of the GNU General Public License version 2 as

# published by the Free Software Foundation.



# This script locates the start of the .data section in xipImage and

# substitutes it with a compressed version. The needed offsets are obtained

# from symbol addresses in vmlinux. It is expected that .data extends to

# the end of xipImage.



set -e



VMLINUX="$1"

XIPIMAGE="$2"



DD="dd status=none"



# Use "make V=1" to debug this script.

case "$KBUILD_VERBOSE" in

*1*)

	set -x

	;;

esac



sym_val() {

	# extract hex value for symbol in $1

	local val=$($NM "$VMLINUX" | sed -n "/ $1$/{s/ .*$//p;q}")

	[ "$val" ] || { echo "can't find $1 in $VMLINUX" 1>&2; exit 1; }

	# convert from hex to decimal

	echo $((0x$val))

}



__data_loc=$(sym_val __data_loc)

_edata_loc=$(sym_val _edata_loc)

base_offset=$(sym_val _xiprom)



# convert to file based offsets

data_start=$(($__data_loc - $base_offset))

data_end=$(($_edata_loc - $base_offset))



# Make sure data occupies the last part of the file.

file_end=$(stat -c "%s" "$XIPIMAGE")

if [ "$file_end" != "$data_end" ]; then

	printf "end of xipImage doesn't match with _edata_loc (%#x vs %#x)\n" \

	       $(($file_end + $base_offset)) $_edata_loc 2>&1

	exit 1;

fi



# be ready to clean up

trap 'rm -f "$XIPIMAGE.tmp"' 0 1 2 3



# substitute the data section by a compressed version

$DD if="$XIPIMAGE" count=$data_start iflag=count_bytes of="$XIPIMAGE.tmp"

$DD if="$XIPIMAGE"  skip=$data_start iflag=skip_bytes |

gzip -9 >> "$XIPIMAGE.tmp"



# replace kernel binary

mv -f "$XIPIMAGE.tmp" "$XIPIMAGE"

arch/arm/kernel/Makefile

+5 −0
Original line number Diff line number Diff line
@@ -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)

arch/arm/kernel/head-common.S

+10 −1
Original line number Diff line number Diff line
@@ -87,7 +87,14 @@ __mmap_switched: 
	adr	r4, __mmap_switched_data

	mov	fp, #0



#ifdef CONFIG_XIP_KERNEL

#if defined(CONFIG_XIP_DEFLATED_DATA)

   ARM(	ldr	sp, [r4], #4 )

 THUMB(	ldr	sp, [r4] )

 THUMB(	add	r4, #4 )

	bl	__inflate_kernel_data		@ decompress .data to RAM

	teq	r0, #0

	bne	__error

#elif defined(CONFIG_XIP_KERNEL)

   ARM(	ldmia	r4!, {r0, r1, r2, sp} )

 THUMB(	ldmia	r4!, {r0, r1, r2, r3} )

 THUMB(	mov	sp, r3 )
@@ -114,9 +121,11 @@ ENDPROC(__mmap_switched) 
	.type	__mmap_switched_data, %object

__mmap_switched_data:

#ifdef CONFIG_XIP_KERNEL

#ifndef CONFIG_XIP_DEFLATED_DATA

	.long	_sdata				@ r0

	.long	__data_loc			@ r1

	.long	_edata_loc			@ r2

#endif

	.long	__bss_stop			@ sp (temporary stack in .bss)

#endif

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