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Date: Sun, 1 Jul 2012 07:55:14 -0700
From: "tip-bot for Eric W. Biederman" <ebiederm@...ssion.com>
To: linux-tip-commits@...r.kernel.org
Cc: linux-kernel@...r.kernel.org, hpa@...or.com, mingo@...nel.org,
tglx@...utronix.de, ebiederm@...ssion.com
Subject: [tip:x86/boot] x86, boot: Don'
t overlap the compressed and non-compressed image
Commit-ID: a1ee43a24ff87a165fe41dcc373d3b7912d0d3fa
Gitweb: http://git.kernel.org/tip/a1ee43a24ff87a165fe41dcc373d3b7912d0d3fa
Author: Eric W. Biederman <ebiederm@...ssion.com>
AuthorDate: Sun, 3 Jun 2012 13:30:49 -0700
Committer: H. Peter Anvin <hpa@...or.com>
CommitDate: Sat, 30 Jun 2012 19:20:39 -0700
x86, boot: Don't overlap the compressed and non-compressed image
In practice there is enough room in the _bss that this doesn't noticably
increase the amount of memory we use during boot, and it makes verifying
the code much simpler.
Signed-off-by: Eric W. Biederman <ebiederm@...ssion.com>
Link: http://lkml.kernel.org/r/87fwacb0jq.fsf_-_@xmission.com
Signed-off-by: H. Peter Anvin <hpa@...or.com>
---
arch/x86/boot/compressed/misc.c | 75 ------------------------------------
arch/x86/boot/compressed/mkpiggy.c | 5 +--
2 files changed, 1 insertions(+), 79 deletions(-)
diff --git a/arch/x86/boot/compressed/misc.c b/arch/x86/boot/compressed/misc.c
index 7116dcb..5b04b66 100644
--- a/arch/x86/boot/compressed/misc.c
+++ b/arch/x86/boot/compressed/misc.c
@@ -18,81 +18,6 @@
*/
/*
- * Getting to provable safe in place decompression is hard.
- * Worst case behaviours need to be analyzed.
- * Background information:
- *
- * The file layout is:
- * magic[2]
- * method[1]
- * flags[1]
- * timestamp[4]
- * extraflags[1]
- * os[1]
- * compressed data blocks[N]
- * crc[4] orig_len[4]
- *
- * resulting in 18 bytes of non compressed data overhead.
- *
- * Files divided into blocks
- * 1 bit (last block flag)
- * 2 bits (block type)
- *
- * 1 block occurs every 32K -1 bytes or when there 50% compression
- * has been achieved. The smallest block type encoding is always used.
- *
- * stored:
- * 32 bits length in bytes.
- *
- * fixed:
- * magic fixed tree.
- * symbols.
- *
- * dynamic:
- * dynamic tree encoding.
- * symbols.
- *
- *
- * The buffer for decompression in place is the length of the
- * uncompressed data, plus a small amount extra to keep the algorithm safe.
- * The compressed data is placed at the end of the buffer. The output
- * pointer is placed at the start of the buffer and the input pointer
- * is placed where the compressed data starts. Problems will occur
- * when the output pointer overruns the input pointer.
- *
- * The output pointer can only overrun the input pointer if the input
- * pointer is moving faster than the output pointer. A condition only
- * triggered by data whose compressed form is larger than the uncompressed
- * form.
- *
- * The worst case at the block level is a growth of the compressed data
- * of 5 bytes per 32767 bytes.
- *
- * The worst case internal to a compressed block is very hard to figure.
- * The worst case can at least be boundined by having one bit that represents
- * 32764 bytes and then all of the rest of the bytes representing the very
- * very last byte.
- *
- * All of which is enough to compute an amount of extra data that is required
- * to be safe. To avoid problems at the block level allocating 5 extra bytes
- * per 32767 bytes of data is sufficient. To avoind problems internal to a
- * block adding an extra 32767 bytes (the worst case uncompressed block size)
- * is sufficient, to ensure that in the worst case the decompressed data for
- * block will stop the byte before the compressed data for a block begins.
- * To avoid problems with the compressed data's meta information an extra 18
- * bytes are needed. Leading to the formula:
- *
- * extra_bytes = (uncompressed_size >> 12) + 32768 + 18 + decompressor_size.
- *
- * Adding 8 bytes per 32K is a bit excessive but much easier to calculate.
- * Adding 32768 instead of 32767 just makes for round numbers.
- * Adding the decompressor_size is necessary as it musht live after all
- * of the data as well. Last I measured the decompressor is about 14K.
- * 10K of actual data and 4K of bss.
- *
- */
-
-/*
* gzip declarations
*/
#define STATIC static
diff --git a/arch/x86/boot/compressed/mkpiggy.c b/arch/x86/boot/compressed/mkpiggy.c
index 958a641..3f4a68d 100644
--- a/arch/x86/boot/compressed/mkpiggy.c
+++ b/arch/x86/boot/compressed/mkpiggy.c
@@ -70,10 +70,7 @@ int main(int argc, char *argv[])
* sizes, compute the necessary decompression offset...
*/
- offs = (olen > ilen) ? olen - ilen : 0;
- offs += olen >> 12; /* Add 8 bytes for each 32K block */
- offs += 64*1024 + 128; /* Add 64K + 128 bytes slack */
- offs = (offs+4095) & ~4095; /* Round to a 4K boundary */
+ offs = (olen+4096) & ~4095; /* Round to a 4K boundary */
printf(".section \".rodata..compressed\",\"a\",@progbits\n");
printf(".globl z_input_len\n");
--
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