path: root/Documentation/x86
diff options
authorNick Terrell <>2020-07-30 12:08:39 -0700
committerIngo Molnar <>2020-07-31 11:49:09 +0200
commitfb46d057db824693994b048d3a8c869892afaa3f (patch)
tree09d43e27af366f91b5845de5fa02ec58b52e5b55 /Documentation/x86
parent0fe4f4ef8cc8e15a8f29f08f4be6128395f125f6 (diff)
x86: Add support for ZSTD compressed kernel
- Add support for zstd compressed kernel - Define __DISABLE_EXPORTS in Makefile - Remove __DISABLE_EXPORTS definition from kaslr.c - Bump the heap size for zstd. - Update the documentation. Integrates the ZSTD decompression code to the x86 pre-boot code. Zstandard requires slightly more memory during the kernel decompression on x86 (192 KB vs 64 KB), and the memory usage is independent of the window size. __DISABLE_EXPORTS is now defined in the Makefile, which covers both the existing use in kaslr.c, and the use needed by the zstd decompressor in misc.c. This patch has been boot tested with both a zstd and gzip compressed kernel on i386 and x86_64 using buildroot and QEMU. Additionally, this has been tested in production on x86_64 devices. We saw a 2 second boot time reduction by switching kernel compression from xz to zstd. Signed-off-by: Nick Terrell <> Signed-off-by: Ingo Molnar <> Tested-by: Sedat Dilek <> Reviewed-by: Kees Cook <> Link:
Diffstat (limited to 'Documentation/x86')
1 files changed, 3 insertions, 3 deletions
diff --git a/Documentation/x86/boot.rst b/Documentation/x86/boot.rst
index 5325c71ca877..7fafc7ac00d7 100644
--- a/Documentation/x86/boot.rst
+++ b/Documentation/x86/boot.rst
@@ -782,9 +782,9 @@ Protocol: 2.08+
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), LZMA
- (magic number 5D 00), XZ (magic number FD 37), and LZ4 (magic number
- 02 21). The uncompressed payload is currently always ELF (magic
- number 7F 45 4C 46).
+ (magic number 5D 00), XZ (magic number FD 37), LZ4 (magic number
+ 02 21) and ZSTD (magic number 28 B5). The uncompressed payload is
+ currently always ELF (magic number 7F 45 4C 46).
============ ==============
Field name: payload_length