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Date: Tue, 10 Mar 2020 10:59:49 +0100
From: Szabolcs Nagy <nsz@...t70.net>
To: musl@...ts.openwall.com
Cc: Kaisrlík@...t70.net, Jan <jan.kaisrlik@...st.com>
Subject: Re: musl and jemalloc support

* Kaisrlík, Jan <jan.kaisrlik@...st.com> [2020-03-10 10:32:08 +0100]:
> I would like to ask about the support of external malloc and jemalloc.
> I find an old mail in ML claiming that support is not there and using
> external malloc function can potentially cause problems[1] and a
> thread[2] on jemalloc saying the same. On the other hand, I find a lot
> of pages comparing speed like pages [3] and also I noticed that Musl
> claims "replacement of malloc is now allowed/supported" statement in
> changelog [4]. So, my expectation is Musl from version 1.1.20 supports
> the loading of external malloc function and it is working. Is my
> assumption correct? Does it have any limitations, e.g., it has to be
> done in compilation time, is LD_PRELOAD supported?

yes, it just works.

> 
> The reason why I'm asking is that some apps started crashing with a
> weird coredump from the moment I used
> LD_PRELOAD=/usr/lib/libjemalloc.so.2:/usr/lib/libpthread.so.

the preloaded libraries obviously have to be built against musl.
(in some cases a glibc linked library would work, i would expect
a glibc linked malloc library to work with musl on x86_64, but
there is no guarantee)

the fact that you have libpthread.so means it's not a musl system
and preloading a libpthread.so from another libc is expected to
crash. (even on other systems you should not just preload libpthread,
but libjemalloc should have it in its dependencies if needed.)

> 
> Thank you for your answer.
> 
> The best,
> Jan
> 
> [1]: https://www.openwall.com/lists/musl/2014/08/08/11
> [2]: https://github.com/jemalloc/jemalloc/issues/1443
> [3]: https://users.rust-lang.org/t/optimizing-rust-binaries-observation-of-musl-versus-glibc-and-jemalloc-versus-system-alloc/8499/7
> [4]: https://git.musl-libc.org/cgit/musl/tree/WHATSNEW#n1916

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