extract-vmlinux 被用来将linux的vmlinuz等文件解析为 vmlinux
分析如下：
#!/bin/sh # shell可执行文件的路径；调试时，保证该执行文件和执行脚本的执行文件一致，否则会导致调试和执行的结果不一致
# SPDX-License-Identifier: GPL-2.0-only
# ----------------------------------------------------------------------
# extract-vmlinux - Extract uncompressed vmlinux from a kernel image
#
# Inspired from extract-ikconfig
# (c) 2009,2010 Dick Streefland <dick@streefland.net>
#
# (c) 2011 Corentin Chary <corentin.chary@gmail.com>
#
# ----------------------------------------------------------------------
check_vmlinux()
{
# Use readelf to check if it's a valid ELF
# TODO: find a better to way to check that it's really vmlinux
# and not just an elf
# readelf -h $1 执行成功将往下走
# > /dev/null 2>&1,标准输出重定向到/dev/null,标准错误重定向到标准输出
readelf -h $1 > /dev/null 2>&1 || return 1
cat $1
exit 0
}
try_decompress()
{
# The obscure use of the "tr" filter is to work around older versions of
# "grep" that report the byte offset of the line instead of the pattern.
# Try to find the header ($1) and decompress from here
# grep -abo "^$2" -a 把二进制文件当作为文本文件，-b 显示匹配字符串的偏移，如：34:matche_string，-o 只显示匹配到的字符串
# tr "$1\n$2" "\n$2=" < "$img" 将$img 文件中的 "$1\n$2" 替换为 "\n$2="
for pos in `tr "$1\n$2" "\n$2=" < "$img" | grep -abo "^$2"`
do
pos=${pos%%:*}
# tail -c+$pos "$img" 显示除了前$pos个字节的所有字节
tail -c+$pos "$img" | $3 > $tmp 2> /dev/null
check_vmlinux $tmp
done
}
# Check invocation:
me=${0##*/}
img=$1
# $#(传入参数数量) -ne(不等于，后接个整数) 1 -o(或) ！-s(文件存在并大小不为0) $img
if [ $# -ne 1 -o ! -s "$img" ]
then
echo "Usage: $me <kernel-image>" >&2
exit 2
fi
# Prepare temp files:
tmp=$(mktemp /tmp/vmlinux-XXX)
# 接收到0信号(退出，定义在signal.h)，将执行"rm -f $tmp"
trap "rm -f $tmp" 0
# That didn't work, so retry after decompression.
try_decompress '\037\213\010' xy gunzip
try_decompress '\3757zXZ\000' abcde unxz
try_decompress 'BZh' xy bunzip2
try_decompress '\135\0\0\0' xxx unlzma
try_decompress '\211\114\132' xy 'lzop -d'
try_decompress '\002!L\030' xxx 'lz4 -d'
try_decompress '(\265/\375' xxx unzstd
# Finally check for uncompressed images or objects:
check_vmlinux $img
# Bail out:
echo "$me: Cannot find vmlinux." >&2
