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authorNicolas Pitre <nicolas.pitre@linaro.org>2017-08-25 00:54:18 -0400
committerNicolas Pitre <nicolas.pitre@linaro.org>2017-09-10 19:34:53 -0400
commitca8b5d97d6bfd2d24cec053bbbe35cf356bec4e3 (patch)
tree36950a2d9a13a56761d182771ebcd795fb17c798
parent0d302c710bf04149b6de7cd9a7064d0ca6cd4bea (diff)
downloadlinux-xip_zdata.tar.gz
ARM: XIP kernel: store .data compressed in ROMxip_zdata
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 <nico@linaro.org> Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> Tested-by: Chris Brandt <Chris.Brandt@renesas.com>
-rw-r--r--arch/arm/Kconfig11
-rw-r--r--arch/arm/boot/Makefile13
-rwxr-xr-xarch/arm/boot/deflate_xip_data.sh64
-rw-r--r--arch/arm/kernel/Makefile5
-rw-r--r--arch/arm/kernel/head-common.S11
-rw-r--r--arch/arm/kernel/head-inflate-data.c62
-rw-r--r--arch/arm/kernel/vmlinux-xip.lds.S8
7 files changed, 172 insertions, 2 deletions
diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index 61a0cb1..bf79c46 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -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)
diff --git a/arch/arm/boot/Makefile b/arch/arm/boot/Makefile
index 50f8d1b..a3af4dc 100644
--- a/arch/arm/boot/Makefile
+++ b/arch/arm/boot/Makefile
@@ -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
diff --git a/arch/arm/boot/deflate_xip_data.sh b/arch/arm/boot/deflate_xip_data.sh
new file mode 100755
index 0000000..1189598
--- /dev/null
+++ b/arch/arm/boot/deflate_xip_data.sh
@@ -0,0 +1,64 @@
+#!/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"
diff --git a/arch/arm/kernel/Makefile b/arch/arm/kernel/Makefile
index ad325a8..52f4379 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)
diff --git a/arch/arm/kernel/head-common.S b/arch/arm/kernel/head-common.S
index bf9c4e3..a25027b 100644
--- a/arch/arm/kernel/head-common.S
+++ b/arch/arm/kernel/head-common.S
@@ -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
diff --git a/arch/arm/kernel/head-inflate-data.c b/arch/arm/kernel/head-inflate-data.c
new file mode 100644
index 0000000..6dd0ce5
--- /dev/null
+++ b/arch/arm/kernel/head-inflate-data.c
@@ -0,0 +1,62 @@
+/*
+ * XIP kernel .data segment decompressor
+ *
+ * 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.
+ */
+
+#include <linux/init.h>
+#include <linux/zutil.h>
+
+/* for struct inflate_state */
+#include "../../../lib/zlib_inflate/inftrees.h"
+#include "../../../lib/zlib_inflate/inflate.h"
+#include "../../../lib/zlib_inflate/infutil.h"
+
+extern char __data_loc[];
+extern char _edata_loc[];
+extern char _sdata[];
+
+/*
+ * This code is called very early during the boot process to decompress
+ * the .data segment stored compressed in ROM. Therefore none of the global
+ * variables are valid yet, hence no kernel services such as memory
+ * allocation is available. Everything must be allocated on the stack and
+ * we must avoid any global data access. We use a temporary stack located
+ * in the .bss area. The linker script makes sure the .bss is big enough
+ * to hold our stack frame plus some room for called functions.
+ *
+ * We mimic the code in lib/decompress_inflate.c to use the smallest work
+ * area possible. And because everything is statically allocated on the
+ * stack then there is no need to clean up before returning.
+ */
+
+int __init __inflate_kernel_data(void)
+{
+ struct z_stream_s stream, *strm = &stream;
+ struct inflate_state state;
+ char *in = __data_loc;
+ int rc;
+
+ /* Check and skip gzip header (assume no filename) */
+ if (in[0] != 0x1f || in[1] != 0x8b || in[2] != 0x08 || in[3] & ~3)
+ return -1;
+ in += 10;
+
+ strm->workspace = &state;
+ strm->next_in = in;
+ strm->avail_in = _edata_loc - __data_loc; /* upper bound */
+ strm->next_out = _sdata;
+ strm->avail_out = _edata_loc - __data_loc;
+ zlib_inflateInit2(strm, -MAX_WBITS);
+ WS(strm)->inflate_state.wsize = 0;
+ WS(strm)->inflate_state.window = NULL;
+ rc = zlib_inflate(strm, Z_FINISH);
+ if (rc == Z_OK || rc == Z_STREAM_END)
+ rc = strm->avail_out; /* should be 0 */
+ return rc;
+}
diff --git a/arch/arm/kernel/vmlinux-xip.lds.S b/arch/arm/kernel/vmlinux-xip.lds.S
index 39b1fb4..7a84431 100644
--- a/arch/arm/kernel/vmlinux-xip.lds.S
+++ b/arch/arm/kernel/vmlinux-xip.lds.S
@@ -306,3 +306,11 @@ ASSERT((__arch_info_end - __arch_info_begin), "no machine record defined")
*/
ASSERT(__hyp_idmap_text_end - (__hyp_idmap_text_start & PAGE_MASK) <= PAGE_SIZE,
"HYP init code too big or misaligned")
+
+#ifdef CONFIG_XIP_DEFLATED_DATA
+/*
+ * The .bss is used as a stack area for __inflate_kernel_data() whose stack
+ * frame is 9568 bytes. Make sure it has extra room left.
+ */
+ASSERT((_end - __bss_start) >= 12288, ".bss too small for CONFIG_XIP_DEFLATED_DATA")
+#endif