scripts/xz_wrap.sh

   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".
  29 is_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.
  36 XZ_VERSION=$($XZ --robot --version) || exit
  37 XZ_VERSION=$(printf '%s\n' "$XZ_VERSION" | sed -n 's/^XZ_VERSION=//p')
  38
  39 # Assume that no BCJ filter is available.
  40 BCJ=
  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.
  46 case $SRCARCH in
  47         arm)
  48                 if is_enabled CONFIG_THUMB2_KERNEL; then
  49                         ALIGN=2
  50                         BCJ=--armthumb
  51                 else
  52                         ALIGN=4
  53                         BCJ=--arm
  54                 fi
  55                 ;;
  56
  57         arm64)
  58                 ALIGN=4
  59
  60                 # ARM64 filter was added in XZ Utils 5.4.0.
  61                 if [ "$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                 ;;
 141 esac
 142
 143 # Select the LZMA2 options matching the instruction alignment.
 144 case $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 ;;
 149 esac
 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.
 162 exec $XZ --check=crc32 --threads=1 $BCJ --lzma2=$LZMA2OPTS,dict=128MiB