x86: support XZ-compressed kernel

This integrates the XZ decompression code to the x86 pre-boot code.

mkpiggy.c is updated to reserve about 32 KiB more buffer safety margin for
kernel decompression.  It is done unconditionally for all decompressors to
keep the code simpler.

The XZ decompressor needs around 30 KiB of heap, so the heap size is
increased to 32 KiB on both x86-32 and x86-64.

Documentation/x86/boot.txt is updated to list the XZ magic number.

With the x86 BCJ filter in XZ, XZ-compressed x86 kernel tends to be a few
percent smaller than the equivalent LZMA-compressed kernel.

Signed-off-by: Lasse Collin <lasse.collin@tukaani.org>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Alain Knaff <alain@knaff.lu>
Cc: Albin Tonnerre <albin.tonnerre@free-electrons.com>
Cc: Phillip Lougher <phillip@lougher.demon.co.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 3 insertions, 3 deletions

diff --git a/Documentation/x86/boot.txt b/Documentation/x86/boot.txt
index bdeb81ccb5f6..9b7221a86df2 100644
--- a/Documentation/x86/boot.txt
+++ b/Documentation/x86/boot.txt
@@ -622,9 +622,9 @@ Protocol:	2.08+
   The payload may be compressed. The format of both the compressed and
   uncompressed data should be determined using the standard magic
   numbers.  The currently supported compression formats are gzip
-  (magic numbers 1F 8B or 1F 9E), bzip2 (magic number 42 5A) and LZMA
-  (magic number 5D 00).  The uncompressed payload is currently always ELF
-  (magic number 7F 45 4C 46).
+  (magic numbers 1F 8B or 1F 9E), bzip2 (magic number 42 5A), LZMA
+  (magic number 5D 00), and XZ (magic number FD 37).  The uncompressed
+  payload is currently always ELF (magic number 7F 45 4C 46).
   
 Field name:     payload_length
 Type:           read