Chimera uses the musl libc. This has a variety of implications:
- Application compatibility may not be as big as with glibc
- Most proprietary applications will not work without flatpak or another container solution
- Proprietary drivers with userland parts will not work at all (most notably the NVIDIA graphics driver)
- Minor performance impact is expected
On the other hand, it has some good aspects:
- A cleaner, leaner codebase with lower resource footprint
- Perfect compatibility with our toolchain, including compiler-rt
- Better security and easier hardening
- It helps expose application bugs and fix them, leading to better code across the software stack
Chimera by default uses the Scudo
allocator (notably also used by default by Android). This is unlike default
musl, which uses its own custom allocator called
As the stock allocator is the primary reason for nearly all performance issues people generally have with musl (fewer CPU-optimized algorithms and so on typically make a negligible impact, while the allocator impact can be very significant), Chimera has chosen to patch in Scudo.
Both the stock allocator and Scudo are hardened allocators focused on security. Musl’s stock allocator is even more so, as it goes as far as keeping a global lock in order to ensure consistency, which in turn leads to poor performance in multithreaded programs, often things that are user-facing/interactive or where performance is otherwise important.
There are, however, scenarios, where one may want to use the stock allocator:
- Those who are particularly security-paranoid and are willing to sacrifice possibly a large chunk of their performance for the peace of mind
- Those for whom memory usage is important to the point of caring about virtual memory; particularly on devices where RAM is very constrained, such as old computers and embedded devices
For most people, the default is going to be fine (i.e. if you are not absolutely sure, you should leave things as they are), however, it does currently use around 120 megabytes of virtual memory per process (keep in mind that this is really virtual memory, not real memory, the real memory usage is very low regardless of the allocator, and Linux default configuration is set up in a way that this will usually not pose a problem; we also intend to further tune the allocator settings in near future).
In any case, there is a way to install the libc with the stock allocator.
The package is called
Do note that installing it is a one-way path. If you wish to revert
back to Scudo afterwards, you need an external system (e.g. a Chimera live
environment) to do manual fixups, or at least a static
If you wish to proceed, create a virtual override first:
# apk add --virtual musl-safety-override
After that, you will be permitted to install the replacement libc:
# apk add musl-mallocng
It is recommended that you do this from a console environment. The machine should be rebooted afterwards.
Reverting to Scudo
If you wish to switch back, this has to be done from an external system
or with a static
apk. This is because the libc is a core component as
musl-mallocng replaces the
musl package, trying to force the stock one
back in will result in
With a static
# apk del musl-mallocng musl-safety-override # apk add musl # ./apk.static fix musl # apk del musl
del is harmless by itself. It will merely remove
musl-safety-override from world, but will not perform any changes.
The second command is where things go wrong;
apk will first install
and subsequently purge
musl-mallocng, which will take
libc.so with it,
resulting in a system that cannot run any binaries.
This is where
apk.static comes in; as it’s static, it can be executed
directly. Therefore, you use it to reinstall
musl. Then regular binaries
should work again, and the last optional
del will just remove
world so it becomes an implicit dependency again.
Doing all this from an external system is a bit safer. If you wish to do that,
mount your system somewhere, including pseudo-filesystems. Have an external
apk ready. Then do something like:
# apk --root /path/to/mount del musl-mallocng musl-safety-override # apk --root /path/to/mount add musl # apk --root /path/to/mount fix musl # apk --root /path/to/mount del musl
Then things should work again.