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1#!/bin/sh
2#
3# This is a wrapper for xz to compress the kernel image using appropriate
4# compression options depending on the architecture.
5#
6# Author: Lasse Collin <lasse.collin@tukaani.org>
7#
8# This file has been put into the public domain.
9# You can do whatever you want with this file.
10#
11
12BCJ=
13LZMA2OPTS=
14
15case $SRCARCH in
16 x86) BCJ=--x86 ;;
17 powerpc) BCJ=--powerpc ;;
18 arm) BCJ=--arm ;;
19 sparc) BCJ=--sparc ;;
20esac
21
22exec $XZ --check=crc32 $BCJ --lzma2=$LZMA2OPTS,dict=32MiB
1#!/bin/sh
2# SPDX-License-Identifier: 0BSD
3#
4# This is a wrapper for xz to compress the kernel image using appropriate
5# compression options depending on the architecture.
6#
7# Author: Lasse Collin <lasse.collin@tukaani.org>
8
9# This has specialized settings for the following archs. However,
10# XZ-compressed kernel isn't currently supported on every listed arch.
11#
12# Arch Align Notes
13# arm 2/4 ARM and ARM-Thumb2
14# arm64 4
15# csky 2
16# loongarch 4
17# mips 2/4 MicroMIPS is 2-byte aligned
18# parisc 4
19# powerpc 4 Uses its own wrapper for compressors instead of this.
20# riscv 2/4
21# s390 2
22# sh 2
23# sparc 4
24# x86 1
25
26# A few archs use 2-byte or 4-byte aligned instructions depending on
27# the kernel config. This function is used to check if the relevant
28# config option is set to "y".
29is_enabled()
30{
31 grep -q "^$1=y$" include/config/auto.conf
32}
33
34# XZ_VERSION is needed to disable features that aren't available in
35# old XZ Utils versions.
36XZ_VERSION=$($XZ --robot --version) || exit
37XZ_VERSION=$(printf '%s\n' "$XZ_VERSION" | sed -n 's/^XZ_VERSION=//p')
38
39# Assume that no BCJ filter is available.
40BCJ=
41
42# Set the instruction alignment to 1, 2, or 4 bytes.
43#
44# Set the BCJ filter if one is available.
45# It must match the #ifdef usage in lib/decompress_unxz.c.
46case $SRCARCH in
47 arm)
48 if is_enabled CONFIG_THUMB2_KERNEL; then
49 ALIGN=2
50 BCJ=--armthumb
51 else
52 ALIGN=4
53 BCJ=--arm
54 fi
55 ;;
56
57 arm64)
58 ALIGN=4
59
60 # ARM64 filter was added in XZ Utils 5.4.0.
61 if [ "$XZ_VERSION" -ge 50040002 ]; then
62 BCJ=--arm64
63 else
64 echo "$0: Upgrading to xz >= 5.4.0" \
65 "would enable the ARM64 filter" \
66 "for better compression" >&2
67 fi
68 ;;
69
70 csky)
71 ALIGN=2
72 ;;
73
74 loongarch)
75 ALIGN=4
76 ;;
77
78 mips)
79 if is_enabled CONFIG_CPU_MICROMIPS; then
80 ALIGN=2
81 else
82 ALIGN=4
83 fi
84 ;;
85
86 parisc)
87 ALIGN=4
88 ;;
89
90 powerpc)
91 ALIGN=4
92
93 # The filter is only for big endian instruction encoding.
94 if is_enabled CONFIG_CPU_BIG_ENDIAN; then
95 BCJ=--powerpc
96 fi
97 ;;
98
99 riscv)
100 if is_enabled CONFIG_RISCV_ISA_C; then
101 ALIGN=2
102 else
103 ALIGN=4
104 fi
105
106 # RISC-V filter was added in XZ Utils 5.6.0.
107 if [ "$XZ_VERSION" -ge 50060002 ]; then
108 BCJ=--riscv
109 else
110 echo "$0: Upgrading to xz >= 5.6.0" \
111 "would enable the RISC-V filter" \
112 "for better compression" >&2
113 fi
114 ;;
115
116 s390)
117 ALIGN=2
118 ;;
119
120 sh)
121 ALIGN=2
122 ;;
123
124 sparc)
125 ALIGN=4
126 BCJ=--sparc
127 ;;
128
129 x86)
130 ALIGN=1
131 BCJ=--x86
132 ;;
133
134 *)
135 echo "$0: Arch-specific tuning is missing for '$SRCARCH'" >&2
136
137 # Guess 2-byte-aligned instructions. Guessing too low
138 # should hurt less than guessing too high.
139 ALIGN=2
140 ;;
141esac
142
143# Select the LZMA2 options matching the instruction alignment.
144case $ALIGN in
145 1) LZMA2OPTS= ;;
146 2) LZMA2OPTS=lp=1 ;;
147 4) LZMA2OPTS=lp=2,lc=2 ;;
148 *) echo "$0: ALIGN wrong or missing" >&2; exit 1 ;;
149esac
150
151# Use single-threaded mode because it compresses a little better
152# (and uses less RAM) than multithreaded mode.
153#
154# For the best compression, the dictionary size shouldn't be
155# smaller than the uncompressed kernel. 128 MiB dictionary
156# needs less than 1400 MiB of RAM in single-threaded mode.
157#
158# On the archs that use this script to compress the kernel,
159# decompression in the preboot code is done in single-call mode.
160# Thus the dictionary size doesn't affect the memory requirements
161# of the preboot decompressor at all.
162exec $XZ --check=crc32 --threads=1 $BCJ --lzma2=$LZMA2OPTS,dict=128MiB