Haha, I don't know how folks found this, but I actually did make it for a real-world use case. While doing large-scale builds of debian packages [1], occasionally I'd have parts of the build process hang (usually some test that I didn't care about). I didn't want the whole build to fail, so I needed some way to kill the process but have it return 0 so that make and friends wouldn't think anything was amiss.
> Note: glibc provides no wrapper for exit_group(), necessitating the use of syscall(2).
Hmm, but elsewhere I find:
> In glibc up to version 2.3, the _exit() wrapper function invoked the kernel system call of the same name. Since glibc 2.3, the wrapper function invokes exit_group(2), in order to terminate all of the threads in a process.
It's not jumping to that address, it's injecting the exit syscall right under the instruction pointer.
If you wanted to modify the register, you'd do `set $rip = 0x050f` without the `{short}`
They're not changing the rip register at all. They're setting the contents of the memory location pointed to by the rip register to 0x050f. The equivalent of "set {x}y = z" in C would be "*(x *)y = z;".
Accidental discharge of gun is a frequent cause of death in the wild, wild united states of guns. Why not also falling out of window, tripping in kitchen with knife, or eating poorly cooked meat, comrade?
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Also, credit where credit is due -- the original idea was suggested to me by Kyle Huey: https://twitter.com/moyix/status/1484342467205816325
[1] https://moyix.blogspot.com/2022/02/on-building-30k-debian-pa...
I found it yesterday on Ukrainian Linux users forum[0], and decided to re-post it on HN ;)
[0] https://linux.org.ua/index.php?topic=11868
http://main.lv/notes/syscalls.md
https://man7.org/linux/man-pages/man2/exit_group.2.html
> Note: glibc provides no wrapper for exit_group(), necessitating the use of syscall(2).
Hmm, but elsewhere I find:
> In glibc up to version 2.3, the _exit() wrapper function invoked the kernel system call of the same name. Since glibc 2.3, the wrapper function invokes exit_group(2), in order to terminate all of the threads in a process.
https://www.man7.org/linux/man-pages/man2/_exit.2.html
It's not jumping to that address, it's injecting the exit syscall right under the instruction pointer. If you wanted to modify the register, you'd do `set $rip = 0x050f` without the `{short}`
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(I love the cell block tango)