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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 <nico@linaro.org> Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> Tested-by: Chris Brandt <Chris.Brandt@renesas.com>
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,64 @@ | ||
| #!/bin/sh | ||
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| # 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. | ||
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| # 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. | ||
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| set -e | ||
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| VMLINUX="$1" | ||
| XIPIMAGE="$2" | ||
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| DD="dd status=none" | ||
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| # Use "make V=1" to debug this script. | ||
| case "$KBUILD_VERBOSE" in | ||
| *1*) | ||
| set -x | ||
| ;; | ||
| esac | ||
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| 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)) | ||
| } | ||
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| __data_loc=$(sym_val __data_loc) | ||
| _edata_loc=$(sym_val _edata_loc) | ||
| base_offset=$(sym_val _xiprom) | ||
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| # convert to file based offsets | ||
| data_start=$(($__data_loc - $base_offset)) | ||
| data_end=$(($_edata_loc - $base_offset)) | ||
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| # Make sure data occupies the last part of the file. | ||
| file_end=$(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)) $_edata_loc 2>&1 | ||
| exit 1; | ||
| fi | ||
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| # be ready to clean up | ||
| trap 'rm -f "$XIPIMAGE.tmp"' 0 1 2 3 | ||
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| # 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" | ||
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| # replace kernel binary | ||
| mv -f "$XIPIMAGE.tmp" "$XIPIMAGE" |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -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. | ||
| */ | ||
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| #include <linux/init.h> | ||
| #include <linux/zutil.h> | ||
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| /* for struct inflate_state */ | ||
| #include "../../../lib/zlib_inflate/inftrees.h" | ||
| #include "../../../lib/zlib_inflate/inflate.h" | ||
| #include "../../../lib/zlib_inflate/infutil.h" | ||
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| extern char __data_loc[]; | ||
| extern char _edata_loc[]; | ||
| extern char _sdata[]; | ||
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| /* | ||
| * 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. | ||
| */ | ||
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| int __init __inflate_kernel_data(void) | ||
| { | ||
| struct z_stream_s stream, *strm = &stream; | ||
| struct inflate_state state; | ||
| char *in = __data_loc; | ||
| int rc; | ||
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| /* 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; | ||
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| 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; | ||
| } |
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