Hacker News Reader

Hacker News

Comment by jwilk | Hacker News Reader

Full thread

jwilk

Interesting projects that employ LD_PRELOAD:

https://github.com/stewartsmith/libeatmydata

https://github.com/wolfcw/libfaketime

https://cwrap.org/

https://github.com/dex4er/fakechroot

https://blitiri.com.ar/p/libfiu/

https://github.com/paultag/tmperamental

View on HN

Here's an idea that I like (so much that I wrote an implementation): use LD_PRELOAD to swap out readline with version that forks on each input. Kill the forked child process and you have undo! https://github.com/thomasballinger/rlundo post: http://ballingt.com/interactive-interpreter-undo/#hacking-fo...

libfaketime can be used for nefarious things such as using software past its trial stage (same with using serials attached to MAC addresses + mac spoofing) or returning future TOTP data. Its generally useful for QA as well. It could've been used by Apple to avoid the reset bug in iOS 11.1.2

fakechroot is used when you build your own *.deb file.

libeatmydata can be used in environments where you'd destroy the data afterwards anyway, or where you don't need logging or keep state after a reboot. You can also mount a bunch of filesystems such as /tmp and /var/log as tmpfs though.

libfaketime is also still crucial for reproduceable builds with a lot of compiers embedding compilation date, too, right?

At least Debian folks didn't have to resort to using libfaketime. Instead, they patch the embedding tools to use timestamp from environment:

https://reproducible-builds.org/specs/source-date-epoch/

> fakechroot is used when you build your own *.deb file.

That's "fakeroot", a different program, which is used for simulating superuser privileges.

I was going to mention fakeroot, too, but it doesn't seem have a useful homepage. https://fakeroot.alioth.debian.org/ looks very much uninviting.

fakeroot was written for Debian, and it's still developed by Debian developers, although there's nothing Debian-specific about it. Debian has giving back to the free software community in their Social Contract¹, but in practice there's no culture of making Debian software easily accessible to outsiders. :-(

¹ https://www.debian.org/social_contract §2

Here's my take on libfaketime, which hooks also hooks syscalls:

https://github.com/DavidBuchanan314/TARDIS

It isn't intended for any kind of serious usage, I mainly just wanted to understand ptrace and LD_PRELOAD.

Onload [1], which is extensively used in some corners of the computing world, also relies on LD_PRELOAD.

[1] http://www.openonload.org/

Addendum: https://github.com/sickill/stderred - colorizing wrapper for stderr

There is also retrace (https://github.com/riboseinc/retrace)

https://github.com/SimonKagstrom/kcov

Also uses LD_PRELOAD.

tsocks [1] is also interesting. It lets you run a program forwarding all its network data through a SOCKS proxy. It's very useful if you want to VPN a single application over a SSH connection.

[1] http://tsocks.sourceforge.net/

Reply on news.ycombinator.com