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This code emulates anexec() system call. That is, it reads an ELF format file,and loads it into memory at the correct address. It then starts the newly-loadedexecutable to running.

All this is usually done by the Linux kernel, so some bizarre things go on.For starters, the userland exec unmaps the currently-executing ELF file,so as to be able to put the new ELF file's contents in the right placein memory.

This code works with 64-bit Linux ELF files, compiled with GCC and linked against glibc.Other C runtimes (Musl libc, for example) cause errors mysterious to me.

Runmake - that should compileexample andulexec.so. Once you'vedone that, you can try it out:

./example ./ulexec.so /usr/bin/cat /proc/self/maps

./example ./ulexec.so./example ./ulexec.so./example ./ulexec.so /usr/bin/cat /proc/self/maps

Yes! You can have it overlay itself with another copy of itself.