75 lines
2.4 KiB
Markdown
75 lines
2.4 KiB
Markdown
`packelf` was inspired by [the idea of Klaus D](https://askubuntu.com/a/546305). It is used to pack a ELF program and its dependent libraries into a single executable file.
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## usage
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```
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Usage: ./packelf.sh [-zjJn] <ELF_SRC_PATH> <DST_PATH> [ADDITIONAL_LIBS ...]
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-zjJ compress flag passed to tar, '-z' by default
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-n pack without compress
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```
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First, pack a ELF program. For example, you can pack `ls` like this:
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```
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# ./packelf.sh /bin/ls /root/ls
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tar: Removing leading `/' from member names
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'/bin/ls' was packed to '/root/ls'
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Just run '/root/ls ARGS...' to execute the command.
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Or run 'PACKELF_UNPACK_DIR=xxx /root/ls' to unpack it only.
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```
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You can execute the packed program directly:
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```
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# /root/ls -lh /root/ls
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-rwxr-xr-x 1 root root 1.3M May 21 08:35 /root/ls
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```
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However, every time the packed program is executed, an internal unpacking operation is performed automatically, which results in a slower startup of the program.
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If you need to execute the program many times and want to reduce the startup time, you can unpack the program before executing it.
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```
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# Run the packed program directly, it takes longer.
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~ # time bash -c 'for i in {1..100};do /root/ls >/dev/null; done'
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real 0m4.203s
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user 0m2.067s
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sys 0m3.093s
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# You can unpack it first.
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~ # PACKELF_UNPACK_DIR=/usr/local/bin /root/ls
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'ls' was unpacked to '/usr/local/bin'.
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You can run '/usr/local/bin/ls ARGS...' to execute the command.
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# ls and ls.res are generated after unpacking.
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~ # /usr/local/bin/ls -lh /usr/local/bin/ls*
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-rwxr-xr-x 1 root root 3.9K May 21 09:00 /usr/local/bin/ls
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/usr/local/bin/ls.res:
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total 3.0M
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-rwxr-xr-x 1 root root 175K May 21 09:00 ld-linux-x86-64.so.2
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-rwxr-xr-x 1 root root 2.0M May 3 2022 libc.so.6
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-rw-r--r-- 1 root root 15K May 3 2022 libdl.so.2
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-rw-r--r-- 1 root root 454K Feb 3 2018 libpcre.so.3
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-rwxr-xr-x 1 root root 142K May 3 2022 libpthread.so.0
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-rw-r--r-- 1 root root 152K Mar 1 2018 libselinux.so.1
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-rwxr-xr-x 1 root root 131K Jan 18 2018 ls
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# Running the unpacked launch script (/usr/local/bin/ls) will take much less time.
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~ # time bash -c 'for i in {1..100};do /usr/local/bin/ls >/dev/null; done'
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real 0m0.370s
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user 0m0.239s
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sys 0m0.133s
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```
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## dependence
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* sh
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* tar
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* sed
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* grep
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* chmod
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* readlink
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* ldd (only needed for packing, not needed for executing or unpacking)
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Note: If your tar doesn't support gzip, '-n' is needed when you pack a program.
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