libpayload: Add LZ4 decompression algorithm

This patch adds support for the LZ4 decompression algorithm to
libpayload. It's what all the cool kids are using for decompression
these days and has many interesting advantages over LZMA (and everything
else I know of): blazing fast decompression (20(!) times faster than
LZMA, twice as fast as LZO on my Cortex-A72), no memory requirements on
decompression, and possibly in-place decompression support. It pays for
that with a lower compression ratio (about 50% larger compressed size
than LZMA, 10% larger than LZO for an ARM64 Linux kernel binary), but
the boot time math still works in its favor for our IO speeds.

This patch only adds the raw decompression functions for use by external
payloads, we can later try integrating them in CBFS. It copies the
decompression code itself unmodified from the upstream LZ4 library at
github.com/Cyan4973/lz4 which will hopefully make it easy to update. The
frame format parsing is reimplemented since the upstream version looks
unnecessarily complex and unreadable for our needs.

BRANCH=smaug
BUG=chrome-os-partner:32184
TEST=With other patches, booted ARM64 kernel that got compressed from
15M to 5.1M and decompresses in 44ms.

Change-Id: I65bdc4b2b19bd51c7b7e17a4e4b79da301a2a014
Signed-off-by: Patrick Georgi <pgeorgi@chromium.org>
Original-Commit-Id: f8a1fc996d5b0234d07f567fa8163d0f802d5144
Original-Change-Id: I15c0620da05561ade2552b15ffdf6bb3afd7eb26
Original-Signed-off-by: Julius Werner <jwerner@chromium.org>
Original-Reviewed-on: https://chromium-review.googlesource.com/282743
Original-Reviewed-by: Stefan Reinauer <reinauer@google.com>
Original-Reviewed-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-on: http://review.coreboot.org/10845
Tested-by: build bot (Jenkins)
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>

7 files changed, 512 insertions, 0 deletions

diff --git a/payloads/libpayload/Kconfig b/payloads/libpayload/Kconfig
index dee970c778..5da4f92ac1 100644
--- a/payloads/libpayload/Kconfig
+++ b/payloads/libpayload/Kconfig
@@ -172,6 +172,13 @@ config LZMA
 	help
 	  LZMA decoder implementation, usable eg. by CBFS,
 	  but also externally.
+
+config LZ4
+	bool "LZ4 decoder"
+	default y
+	help
+	  Decoder implementation for the LZ4 compression algorithm.
+	  Adds standalone functions (CBFS support coming soon).
 endmenu
 
 menu "Console Options"
diff --git a/payloads/libpayload/LICENSES b/payloads/libpayload/LICENSES
index f340eadb7d..ab8daa46df 100644
--- a/payloads/libpayload/LICENSES
+++ b/payloads/libpayload/LICENSES
@@ -131,3 +131,7 @@ holders, and the exact license terms that apply.
   Source: GNU C Library (glibc), http://www.gnu.org/software/libc/libc.html
   Original files: sysdeps/i386/memset.c
   Current version we use: 2.14
+
+* liblz4/lz4.c: 2-clause BSD
+  Source: LZ4 library, https://github.com/Cyan4973/lz4
+  Current version we use: r130 (baf78e7e4dcbdf824a76f990ffeb573d113bbbdb)
diff --git a/payloads/libpayload/Makefile.inc b/payloads/libpayload/Makefile.inc
index c8a49fc281..b84e322941 100644
--- a/payloads/libpayload/Makefile.inc
+++ b/payloads/libpayload/Makefile.inc
@@ -45,6 +45,7 @@ classes-$(CONFIG_LP_CURSES) += libcurses
 classes-$(CONFIG_LP_PDCURSES) += libmenu libform libpanel
 classes-$(CONFIG_LP_CBFS) += libcbfs
 classes-$(CONFIG_LP_LZMA) += liblzma
+classes-$(CONFIG_LP_LZ4) += liblz4
 classes-$(CONFIG_LP_REMOTEGDB) += libgdb
 libraries := $(classes-y)
 classes-y += head.o
@@ -54,6 +55,7 @@ subdirs-y += crypto libc drivers libpci gdb
 subdirs-$(CONFIG_LP_CURSES) += curses
 subdirs-$(CONFIG_LP_CBFS) += libcbfs
 subdirs-$(CONFIG_LP_LZMA) += liblzma
+subdirs-$(CONFIG_LP_LZ4) += liblz4
 
 INCLUDES := -Iinclude -Iinclude/$(ARCHDIR-y) -I$(obj) -include include/kconfig.h
 
diff --git a/payloads/libpayload/include/lz4.h b/payloads/libpayload/include/lz4.h
new file mode 100644
index 0000000000..1f2830db46
--- /dev/null
+++ b/payloads/libpayload/include/lz4.h
@@ -0,0 +1,47 @@
+/*
+ * Copyright 2015 Google Inc.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 3. The name of the author may not be used to endorse or promote products
+ *    derived from this software without specific prior written permission.
+ *
+ * Alternatively, this software may be distributed under the terms of the
+ * GNU General Public License ("GPL") version 2 as published by the Free
+ * Software Foundation.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#ifndef __LZ4_H_
+#define __LZ4_H_
+
+#include <stddef.h>
+
+/* Decompresses an LZ4F image (multiple LZ4 blocks with frame header) from src
+ * to dst, ensuring that it doesn't read more than srcn bytes and doesn't write
+ * more than dstn. Buffer sizes must stay below 2GB.
+ * Returns amount of decompressed bytes, or 0 on error.
+ */
+size_t ulz4fn(const void *src, size_t srcn, void *dst, size_t dstn);
+
+/* Same as ulz4fn() but does not perform any bounds checks. */
+size_t ulz4f(const void *src, void *dst);
+
+#endif /* __LZO_H_ */
diff --git a/payloads/libpayload/liblz4/Makefile.inc b/payloads/libpayload/liblz4/Makefile.inc
new file mode 100644
index 0000000000..272a5a5c46
--- /dev/null
+++ b/payloads/libpayload/liblz4/Makefile.inc
@@ -0,0 +1,28 @@
+##
+## Copyright 2015 Google Inc.
+##
+## Redistribution and use in source and binary forms, with or without
+## modification, are permitted provided that the following conditions
+## are met:
+## 1. Redistributions of source code must retain the above copyright
+##    notice, this list of conditions and the following disclaimer.
+## 2. Redistributions in binary form must reproduce the above copyright
+##    notice, this list of conditions and the following disclaimer in the
+##    documentation and/or other materials provided with the distribution.
+## 3. The name of the author may not be used to endorse or promote products
+##    derived from this software without specific prior written permission.
+##
+## THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+## ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+## IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+## ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
+## FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+## DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+## OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+## HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+## LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+## OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+## SUCH DAMAGE.
+##
+
+liblz4-$(CONFIG_LP_LZ4) += lz4_wrapper.c
diff --git a/payloads/libpayload/liblz4/lz4.c b/payloads/libpayload/liblz4/lz4.c
new file mode 100644
index 0000000000..fb89090ee2
--- /dev/null
+++ b/payloads/libpayload/liblz4/lz4.c
@@ -0,0 +1,266 @@
+/*
+   LZ4 - Fast LZ compression algorithm
+   Copyright (C) 2011-2015, Yann Collet.
+
+   BSD 2-Clause License (http://www.opensource.org/licenses/bsd-license.php)
+
+   Redistribution and use in source and binary forms, with or without
+   modification, are permitted provided that the following conditions are
+   met:
+
+       * Redistributions of source code must retain the above copyright
+   notice, this list of conditions and the following disclaimer.
+       * Redistributions in binary form must reproduce the above
+   copyright notice, this list of conditions and the following disclaimer
+   in the documentation and/or other materials provided with the
+   distribution.
+
+   THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+   "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+   LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+   A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+   OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+   SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+   LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+   DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+   THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+   (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+   OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+   You can contact the author at :
+   - LZ4 source repository : https://github.com/Cyan4973/lz4
+   - LZ4 public forum : https://groups.google.com/forum/#!forum/lz4c
+*/
+
+
+/**************************************
+*  Reading and writing into memory
+**************************************/
+
+/* customized version of memcpy, which may overwrite up to 7 bytes beyond dstEnd */
+static void LZ4_wildCopy(void* dstPtr, const void* srcPtr, void* dstEnd)
+{
+    BYTE* d = (BYTE*)dstPtr;
+    const BYTE* s = (const BYTE*)srcPtr;
+    BYTE* e = (BYTE*)dstEnd;
+    do { LZ4_copy8(d,s); d+=8; s+=8; } while (d<e);
+}
+
+
+/**************************************
+*  Common Constants
+**************************************/
+#define MINMATCH 4
+
+#define COPYLENGTH 8
+#define LASTLITERALS 5
+#define MFLIMIT (COPYLENGTH+MINMATCH)
+static const int LZ4_minLength = (MFLIMIT+1);
+
+#define KB *(1 <<10)
+#define MB *(1 <<20)
+#define GB *(1U<<30)
+
+#define MAXD_LOG 16
+#define MAX_DISTANCE ((1 << MAXD_LOG) - 1)
+
+#define ML_BITS  4
+#define ML_MASK  ((1U<<ML_BITS)-1)
+#define RUN_BITS (8-ML_BITS)
+#define RUN_MASK ((1U<<RUN_BITS)-1)
+
+
+/**************************************
+*  Local Structures and types
+**************************************/
+typedef enum { noDict = 0, withPrefix64k, usingExtDict } dict_directive;
+typedef enum { endOnOutputSize = 0, endOnInputSize = 1 } endCondition_directive;
+typedef enum { full = 0, partial = 1 } earlyEnd_directive;
+
+
+
+/*******************************
+*  Decompression functions
+*******************************/
+/*
+ * This generic decompression function cover all use cases.
+ * It shall be instantiated several times, using different sets of directives
+ * Note that it is essential this generic function is really inlined,
+ * in order to remove useless branches during compilation optimization.
+ */
+FORCE_INLINE int LZ4_decompress_generic(
+                 const char* const source,
+                 char* const dest,
+                 int inputSize,
+                 int outputSize,         /* If endOnInput==endOnInputSize, this value is the max size of Output Buffer. */
+
+                 int endOnInput,         /* endOnOutputSize, endOnInputSize */
+                 int partialDecoding,    /* full, partial */
+                 int targetOutputSize,   /* only used if partialDecoding==partial */
+                 int dict,               /* noDict, withPrefix64k, usingExtDict */
+                 const BYTE* const lowPrefix,  /* == dest if dict == noDict */
+                 const BYTE* const dictStart,  /* only if dict==usingExtDict */
+                 const size_t dictSize         /* note : = 0 if noDict */
+                 )
+{
+    /* Local Variables */
+    const BYTE* ip = (const BYTE*) source;
+    const BYTE* const iend = ip + inputSize;
+
+    BYTE* op = (BYTE*) dest;
+    BYTE* const oend = op + outputSize;
+    BYTE* cpy;
+    BYTE* oexit = op + targetOutputSize;
+    const BYTE* const lowLimit = lowPrefix - dictSize;
+
+    const BYTE* const dictEnd = (const BYTE*)dictStart + dictSize;
+    const size_t dec32table[] = {4, 1, 2, 1, 4, 4, 4, 4};
+    const size_t dec64table[] = {0, 0, 0, (size_t)-1, 0, 1, 2, 3};
+
+    const int safeDecode = (endOnInput==endOnInputSize);
+    const int checkOffset = ((safeDecode) && (dictSize < (int)(64 KB)));
+
+
+    /* Special cases */
+    if ((partialDecoding) && (oexit> oend-MFLIMIT)) oexit = oend-MFLIMIT;                         /* targetOutputSize too high => decode everything */
+    if ((endOnInput) && (unlikely(outputSize==0))) return ((inputSize==1) && (*ip==0)) ? 0 : -1;  /* Empty output buffer */
+    if ((!endOnInput) && (unlikely(outputSize==0))) return (*ip==0?1:-1);
+
+
+    /* Main Loop */
+    while (1)
+    {
+        unsigned token;
+        size_t length;
+        const BYTE* match;
+
+        /* get literal length */
+        token = *ip++;
+        if ((length=(token>>ML_BITS)) == RUN_MASK)
+        {
+            unsigned s;
+            do
+            {
+                s = *ip++;
+                length += s;
+            }
+            while (likely((endOnInput)?ip<iend-RUN_MASK:1) && (s==255));
+            if ((safeDecode) && unlikely((size_t)(op+length)<(size_t)(op))) goto _output_error;   /* overflow detection */
+            if ((safeDecode) && unlikely((size_t)(ip+length)<(size_t)(ip))) goto _output_error;   /* overflow detection */
+        }
+
+        /* copy literals */
+        cpy = op+length;
+        if (((endOnInput) && ((cpy>(partialDecoding?oexit:oend-MFLIMIT)) || (ip+length>iend-(2+1+LASTLITERALS))) )
+            || ((!endOnInput) && (cpy>oend-COPYLENGTH)))
+        {
+            if (partialDecoding)
+            {
+                if (cpy > oend) goto _output_error;                           /* Error : write attempt beyond end of output buffer */
+                if ((endOnInput) && (ip+length > iend)) goto _output_error;   /* Error : read attempt beyond end of input buffer */
+            }
+            else
+            {
+                if ((!endOnInput) && (cpy != oend)) goto _output_error;       /* Error : block decoding must stop exactly there */
+                if ((endOnInput) && ((ip+length != iend) || (cpy > oend))) goto _output_error;   /* Error : input must be consumed */
+            }
+            memcpy(op, ip, length);
+            ip += length;
+            op += length;
+            break;     /* Necessarily EOF, due to parsing restrictions */
+        }
+        LZ4_wildCopy(op, ip, cpy);
+        ip += length; op = cpy;
+
+        /* get offset */
+        match = cpy - LZ4_readLE16(ip); ip+=2;
+        if ((checkOffset) && (unlikely(match < lowLimit))) goto _output_error;   /* Error : offset outside destination buffer */
+
+        /* get matchlength */
+        length = token & ML_MASK;
+        if (length == ML_MASK)
+        {
+            unsigned s;
+            do
+            {
+                if ((endOnInput) && (ip > iend-LASTLITERALS)) goto _output_error;
+                s = *ip++;
+                length += s;
+            } while (s==255);
+            if ((safeDecode) && unlikely((size_t)(op+length)<(size_t)op)) goto _output_error;   /* overflow detection */
+        }
+        length += MINMATCH;
+
+        /* check external dictionary */
+        if ((dict==usingExtDict) && (match < lowPrefix))
+        {
+            if (unlikely(op+length > oend-LASTLITERALS)) goto _output_error;   /* doesn't respect parsing restriction */
+
+            if (length <= (size_t)(lowPrefix-match))
+            {
+                /* match can be copied as a single segment from external dictionary */
+                match = dictEnd - (lowPrefix-match);
+                memmove(op, match, length); op += length;
+            }
+            else
+            {
+                /* match encompass external dictionary and current segment */
+                size_t copySize = (size_t)(lowPrefix-match);
+                memcpy(op, dictEnd - copySize, copySize);
+                op += copySize;
+                copySize = length - copySize;
+                if (copySize > (size_t)(op-lowPrefix))   /* overlap within current segment */
+                {
+                    BYTE* const endOfMatch = op + copySize;
+                    const BYTE* copyFrom = lowPrefix;
+                    while (op < endOfMatch) *op++ = *copyFrom++;
+                }
+                else
+                {
+                    memcpy(op, lowPrefix, copySize);
+                    op += copySize;
+                }
+            }
+            continue;
+        }
+
+        /* copy repeated sequence */
+        cpy = op + length;
+        if (unlikely((op-match)<8))
+        {
+            const size_t dec64 = dec64table[op-match];
+            op[0] = match[0];
+            op[1] = match[1];
+            op[2] = match[2];
+            op[3] = match[3];
+            match += dec32table[op-match];
+            LZ4_copy4(op+4, match);
+            op += 8; match -= dec64;
+        } else { LZ4_copy8(op, match); op+=8; match+=8; }
+
+        if (unlikely(cpy>oend-12))
+        {
+            if (cpy > oend-LASTLITERALS) goto _output_error;    /* Error : last LASTLITERALS bytes must be literals */
+            if (op < oend-8)
+            {
+                LZ4_wildCopy(op, match, oend-8);
+                match += (oend-8) - op;
+                op = oend-8;
+            }
+            while (op<cpy) *op++ = *match++;
+        }
+        else
+            LZ4_wildCopy(op, match, cpy);
+        op=cpy;   /* correction */
+    }
+
+    /* end of decoding */
+    if (endOnInput)
+       return (int) (((char*)op)-dest);     /* Nb of output bytes decoded */
+    else
+       return (int) (((const char*)ip)-source);   /* Nb of input bytes read */
+
+    /* Overflow error detected */
+_output_error:
+    return (int) (-(((const char*)ip)-source))-1;
+}
diff --git a/payloads/libpayload/liblz4/lz4_wrapper.c b/payloads/libpayload/liblz4/lz4_wrapper.c
new file mode 100644
index 0000000000..b04659783d
--- /dev/null
+++ b/payloads/libpayload/liblz4/lz4_wrapper.c
@@ -0,0 +1,158 @@
+/*
+ * Copyright 2015 Google Inc.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 3. The name of the author may not be used to endorse or promote products
+ *    derived from this software without specific prior written permission.
+ *
+ * Alternatively, this software may be distributed under the terms of the
+ * GNU General Public License ("GPL") version 2 as published by the Free
+ * Software Foundation.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#include <assert.h>
+#include <endian.h>
+#include <libpayload.h>
+#include <lz4.h>
+
+/* LZ4 comes with its own supposedly portable memory access functions, but they
+ * seem to be very inefficient in practice (at least on ARM64). Since libpayload
+ * knows about endinaness and allows some basic assumptions (such as unaligned
+ * access support), we can easily write the ones we need ourselves. */
+static u16 LZ4_readLE16(const void *src) { return le16toh(*(u16 *)src); }
+static void LZ4_copy4(void *dst, const void *src) { *(u32 *)dst = *(u32 *)src; }
+static void LZ4_copy8(void *dst, const void *src) { *(u64 *)dst = *(u64 *)src; }
+
+typedef  uint8_t BYTE;
+typedef uint16_t U16;
+typedef uint32_t U32;
+typedef  int32_t S32;
+typedef uint64_t U64;
+
+#define FORCE_INLINE static inline __attribute__((always_inline))
+#define likely(expr) __builtin_expect((expr) != 0, 1)
+#define unlikely(expr) __builtin_expect((expr) != 0, 0)
+
+/* Unaltered (except removing unrelated code) from github.com/Cyan4973/lz4. */
+#include "lz4.c"	/* #include for inlining, do not link! */
+
+#define LZ4F_MAGICNUMBER 0x184D2204
+
+struct lz4_frame_header {
+	u32 magic;
+	union {
+		u8 flags;
+		struct {
+			u8 reserved0		: 2;
+			u8 has_content_checksum	: 1;
+			u8 has_content_size	: 1;
+			u8 has_block_checksum	: 1;
+			u8 independent_blocks	: 1;
+			u8 version		: 2;
+		};
+	};
+	union {
+		u8 block_descriptor;
+		struct {
+			u8 reserved1		: 4;
+			u8 max_block_size	: 3;
+			u8 reserved2		: 1;
+		};
+	};
+	/* + u64 content_size iff has_content_size is set */
+	/* + u8 header_checksum */
+} __attribute__((packed));
+
+struct lz4_block_header {
+	union {
+		u32 raw;
+		struct {
+			u32 size		: 31;
+			u32 not_compressed	: 1;
+		};
+	};
+	/* + size bytes of data */
+	/* + u32 block_checksum iff has_block_checksum is set */
+} __attribute__((packed));
+
+size_t ulz4fn(const void *src, size_t srcn, void *dst, size_t dstn)
+{
+	const void *in = src;
+	void *out = dst;
+	int has_block_checksum;
+
+	{ /* With in-place decompression the header may become invalid later. */
+		const struct lz4_frame_header *h = in;
+
+		if (srcn < sizeof(*h) + sizeof(u64) + sizeof(u8))
+			return 0;	/* input overrun */
+
+		/* We assume there's always only a single, standard frame. */
+		if (le32toh(h->magic) != LZ4F_MAGICNUMBER || h->version != 1)
+			return 0;	/* unknown format */
+		if (h->reserved0 || h->reserved1 || h->reserved2)
+			return 0;	/* reserved must be zero */
+		if (!h->independent_blocks)
+			return 0;	/* we don't support block dependency */
+		has_block_checksum = h->has_block_checksum;
+
+		in += sizeof(*h);
+		if (h->has_content_size)
+			in += sizeof(u64);
+		in += sizeof(u8);
+	}
+
+	while (1) {
+		struct lz4_block_header b = { .raw = le32toh(*(u32 *)in) };
+		in += sizeof(struct lz4_block_header);
+
+		if (in - src + b.size > srcn)
+			return 0;		/* input overrun */
+
+		if (!b.size)
+			return out - dst;	/* decompression successful */
+
+		if (b.not_compressed) {
+			memcpy(out, in, b.size);
+			out += b.size;
+		} else {
+			/* constant folding essential, do not touch params! */
+			int ret = LZ4_decompress_generic(in, out, b.size,
+					dst + dstn - out, endOnInputSize,
+					full, 0, noDict, out, NULL, 0);
+			if (ret < 0)
+				return 0;	/* decompression error */
+			else
+				out += ret;
+		}
+
+		in += b.size;
+		if (has_block_checksum)
+			in += sizeof(u32);
+	}
+}
+
+size_t ulz4f(const void *src, void *dst)
+{
+	/* LZ4 uses signed size parameters, so can't just use ((u32)-1) here. */
+	return ulz4fn(src, 1*GiB, dst, 1*GiB);
+}