Commit-ID: a1ee43a24ff87a165fe41dcc373d3b7912d0d3fa Gitweb: http://git.kernel.org/tip/a1ee43a24ff87a165fe41dcc373d3b7912d0d3fa Author: Eric W. Biederman <ebiederm@xxxxxxxxxxxx> AuthorDate: Sun, 3 Jun 2012 13:30:49 -0700 Committer: H. Peter Anvin <hpa@xxxxxxxxx> 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@xxxxxxxxxxxx> Link: http://lkml.kernel.org/r/87fwacb0jq.fsf_-_@xxxxxxxxxxxx Signed-off-by: H. Peter Anvin <hpa@xxxxxxxxx> --- 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"); -- To unsubscribe from this list: send the line "unsubscribe linux-tip-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html