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lz4 compatible decompressor is simple. The format is underspecified and relies on EOF notification to determine when to stop. Initramfs buffer format[1] explicitly states that it can have arbitrary number of zero padding. Thus when operating without a fill function, be extra careful to ensure that sizes less than 4, or apperantly empty chunksizes are treated as EOF. To test this I have created two cpio initrds, first a normal one, main.cpio. And second one with just a single /test-file with content "second" second.cpio. Then i compressed both of them with gzip, and with lz4 -l. Then I created a padding of 4 bytes (dd if=/dev/zero of=pad4 bs=1 count=4). To create four testcase initrds: 1) main.cpio.gzip + extra.cpio.gzip = pad0.gzip 2) main.cpio.lz4 + extra.cpio.lz4 = pad0.lz4 3) main.cpio.gzip + pad4 + extra.cpio.gzip = pad4.gzip 4) main.cpio.lz4 + pad4 + extra.cpio.lz4 = pad4.lz4 The pad4 test-cases replicate the initrd load by grub, as it pads and aligns every initrd it loads. All of the above boot, however /test-file was not accessible in the initrd for the testcase #4, as decoding in lz4 decompressor failed. Also an error message printed which usually is harmless. Whith a patched kernel, all of the above testcases now pass, and /test-file is accessible. This fixes lz4 initrd decompress warning on every boot with grub. And more importantly this fixes inability to load multiple lz4 compressed initrds with grub. This patch has been shipping in Ubuntu kernels since January 2021. [1] ./Documentation/driver-api/early-userspace/buffer-format.rst BugLink: https://bugs.launchpad.net/bugs/1835660 Link: https://lore.kernel.org/lkml/20210114200256.196589-1-xnox@ubuntu.com/ # v0 Link: https://lkml.kernel.org/r/20210513104831.432975-1-dimitri.ledkov@canonical.com Signed-off-by: Dimitri John Ledkov <dimitri.ledkov@canonical.com> Cc: Kyungsik Lee <kyungsik.lee@lge.com> Cc: Yinghai Lu <yinghai@kernel.org> Cc: Bongkyu Kim <bongkyu.kim@lge.com> Cc: Kees Cook <keescook@chromium.org> Cc: Sven Schmidt <4sschmid@informatik.uni-hamburg.de> Cc: Rajat Asthana <thisisrast7@gmail.com> Cc: Nick Terrell <terrelln@fb.com> Cc: Gao Xiang <hsiangkao@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
218 lines
4.2 KiB
C
218 lines
4.2 KiB
C
// SPDX-License-Identifier: GPL-2.0-only
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/*
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* Wrapper for decompressing LZ4-compressed kernel, initramfs, and initrd
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*
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* Copyright (C) 2013, LG Electronics, Kyungsik Lee <kyungsik.lee@lge.com>
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*/
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#ifdef STATIC
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#define PREBOOT
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#include "lz4/lz4_decompress.c"
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#else
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#include <linux/decompress/unlz4.h>
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#endif
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#include <linux/types.h>
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#include <linux/lz4.h>
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#include <linux/decompress/mm.h>
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#include <linux/compiler.h>
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#include <asm/unaligned.h>
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/*
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* Note: Uncompressed chunk size is used in the compressor side
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* (userspace side for compression).
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* It is hardcoded because there is not proper way to extract it
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* from the binary stream which is generated by the preliminary
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* version of LZ4 tool so far.
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*/
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#define LZ4_DEFAULT_UNCOMPRESSED_CHUNK_SIZE (8 << 20)
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#define ARCHIVE_MAGICNUMBER 0x184C2102
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STATIC inline int INIT unlz4(u8 *input, long in_len,
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long (*fill)(void *, unsigned long),
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long (*flush)(void *, unsigned long),
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u8 *output, long *posp,
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void (*error) (char *x))
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{
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int ret = -1;
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size_t chunksize = 0;
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size_t uncomp_chunksize = LZ4_DEFAULT_UNCOMPRESSED_CHUNK_SIZE;
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u8 *inp;
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u8 *inp_start;
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u8 *outp;
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long size = in_len;
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#ifdef PREBOOT
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size_t out_len = get_unaligned_le32(input + in_len);
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#endif
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size_t dest_len;
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if (output) {
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outp = output;
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} else if (!flush) {
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error("NULL output pointer and no flush function provided");
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goto exit_0;
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} else {
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outp = large_malloc(uncomp_chunksize);
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if (!outp) {
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error("Could not allocate output buffer");
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goto exit_0;
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}
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}
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if (input && fill) {
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error("Both input pointer and fill function provided,");
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goto exit_1;
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} else if (input) {
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inp = input;
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} else if (!fill) {
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error("NULL input pointer and missing fill function");
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goto exit_1;
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} else {
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inp = large_malloc(LZ4_compressBound(uncomp_chunksize));
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if (!inp) {
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error("Could not allocate input buffer");
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goto exit_1;
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}
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}
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inp_start = inp;
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if (posp)
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*posp = 0;
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if (fill) {
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size = fill(inp, 4);
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if (size < 4) {
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error("data corrupted");
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goto exit_2;
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}
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}
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chunksize = get_unaligned_le32(inp);
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if (chunksize == ARCHIVE_MAGICNUMBER) {
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if (!fill) {
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inp += 4;
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size -= 4;
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}
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} else {
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error("invalid header");
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goto exit_2;
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}
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if (posp)
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*posp += 4;
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for (;;) {
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if (fill) {
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size = fill(inp, 4);
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if (size == 0)
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break;
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if (size < 4) {
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error("data corrupted");
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goto exit_2;
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}
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} else if (size < 4) {
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/* empty or end-of-file */
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goto exit_3;
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}
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chunksize = get_unaligned_le32(inp);
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if (chunksize == ARCHIVE_MAGICNUMBER) {
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if (!fill) {
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inp += 4;
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size -= 4;
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}
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if (posp)
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*posp += 4;
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continue;
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}
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if (!fill && chunksize == 0) {
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/* empty or end-of-file */
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goto exit_3;
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}
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if (posp)
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*posp += 4;
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if (!fill) {
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inp += 4;
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size -= 4;
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} else {
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if (chunksize > LZ4_compressBound(uncomp_chunksize)) {
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error("chunk length is longer than allocated");
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goto exit_2;
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}
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size = fill(inp, chunksize);
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if (size < chunksize) {
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error("data corrupted");
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goto exit_2;
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}
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}
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#ifdef PREBOOT
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if (out_len >= uncomp_chunksize) {
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dest_len = uncomp_chunksize;
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out_len -= dest_len;
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} else
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dest_len = out_len;
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ret = LZ4_decompress_fast(inp, outp, dest_len);
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chunksize = ret;
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#else
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dest_len = uncomp_chunksize;
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ret = LZ4_decompress_safe(inp, outp, chunksize, dest_len);
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dest_len = ret;
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#endif
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if (ret < 0) {
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error("Decoding failed");
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goto exit_2;
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}
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ret = -1;
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if (flush && flush(outp, dest_len) != dest_len)
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goto exit_2;
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if (output)
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outp += dest_len;
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if (posp)
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*posp += chunksize;
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if (!fill) {
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size -= chunksize;
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if (size == 0)
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break;
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else if (size < 0) {
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error("data corrupted");
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goto exit_2;
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}
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inp += chunksize;
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}
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}
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exit_3:
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ret = 0;
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exit_2:
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if (!input)
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large_free(inp_start);
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exit_1:
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if (!output)
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large_free(outp);
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exit_0:
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return ret;
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}
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#ifdef PREBOOT
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STATIC int INIT __decompress(unsigned char *buf, long in_len,
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long (*fill)(void*, unsigned long),
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long (*flush)(void*, unsigned long),
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unsigned char *output, long out_len,
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long *posp,
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void (*error)(char *x)
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)
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{
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return unlz4(buf, in_len - 4, fill, flush, output, posp, error);
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}
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#endif
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