linux-6.12.1/lib/decompress_unxz.c

1 // SPDX-License-Identifier: 0BSD
4  * Wrapper for decompressing XZ-compressed kernel, initramfs, and initrd
10  * Important notes about in-place decompression
20  * The worst case for in-place decompression is that the beginning of
22  * incompressible. Thus, we must look for worst-case expansion when the
29  *    Block Header:
30  *      Block Header (8-12)
32  *      Block Padding (0-3)
34  *    Index (8-20)
37  * Normally there is exactly one Block, but let's assume that there are
38  * 2-4 Blocks just in case. Because Stream Header and also Block Header
39  * of the first Block don't make the decompressor produce any uncompressed
40  * data, we can ignore them from our calculations. Block Headers of possible
73  *   - 128 bytes for the .xz file format headers;
74  *   - 8 bytes per every 32 KiB of uncompressed size (one LZMA2 chunk header
76  *   - 64 KiB (biggest possible LZMA2 chunk payload size) to make sure that
90  * Thus, when updating Deflate-only in-place kernel decompressor to
97  * decompression (pre-boot code). <linux/decompress/mm.h> will define
157  * when XZ_DYNALLOC is used, but the pre-boot free() doesn't support it.
170  * FIXME: Not all basic memory functions are provided in architecture-specific
175  * is fast enough. memcpy/memmove speed matters in multi-call mode, but
176  * the kernel image is decompressed in single-call mode, in which only
222 		while (i-- > 0)  in memmove()
247 /* Size of the input and output buffers in multi-call mode */
253  * This wrapper will automatically choose single-call or multi-call mode
254  * of the native XZ decoder API. The single-call mode can be used only when
279 		s = xz_dec_init(XZ_DYNALLOC, (uint32_t)-1);  in unxz()
286 		b.out_size = (size_t)-1;  in unxz()
363 		/* This can occur only in multi-call mode. */  in unxz()
378 		error("XZ-compressed data is corrupt");  in unxz()
386 	return -1;  in unxz()
397 	return -1;  in unxz()
401  * This function is used by architecture-specific files to decompress