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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