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Date: Sat, 29 Mar 2014 19:15:02 +0200
From: Timo Teras <timo.teras@....fi>
To: musl@...ts.openwall.com
Cc: u-igbb@...ey.se
Subject: Re: malloc not behaving well when brk space is limited?
On Sat, 29 Mar 2014 17:00:32 +0000
u-igbb@...ey.se wrote:
> Background:
> Compiling a native musl-based toolchain for ia32 on Linux 2.6+.
> Using the standalone dynamic loader mode.
> (The latter seems to lead to a quite limited heap space, by kernel
> behaviour/design)
>
> I encounter out of memory errors. A look at the malloc source does not
> find any fallback to mmap when heap is exhausted. What would you
> suggest as a suitable approach to make it work?
>
> Somebody has possibly already encountered and solved this with musl?
Yes, been there done that. I patched kernel.
The thread that follows on sending the patch upstream is e.g. at:
https://groups.google.com/forum/#!msg/linux.kernel/mOf1EWrrhZc/bl96BAE4fyQJ
Also using grsec kernel would fix the issue mostly, since grsec creates
"better" memory layout for PIE binaries.
> I see also reports about a related out of memory problem with
> pae-executables which means a solution might help many musl users.
>
> The other standard libraries I am using (glibc, uclibc) seem to
> happily switch to allocation from mmap() when the heap is full. I
> understand that this costs some code and performance but a breakup is
> no good either.
>
> Any ideas? Maintaining and using an external libmalloc or substituting
> malloc in musl? This feels like quite a burden...
> (Would musl internal calls to malloc notice the external library
> and resolve to its entry points instead of the internal malloc?)
musl does not support external malloc. musl internal calls to
malloc() are not overridable.
I think you need to fix kernel. Rewrite allocator in musl. Or add the
fallback code to mmap - but dalias said it's "hard". Perhaps still
should be still reconsidered.
- Timo
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