#13447: Make libsingular multivariate polynomial rings collectable
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Reporter: nbruin | Owner: rlm
Type: defect | Status: new
Priority: major | Milestone:
sage-5.4
Component: memleak | Resolution:
Keywords: | Work issues:
Report Upstream: Reported upstream. No feedback yet. | Reviewers:
Authors: | Merged in:
Dependencies: | Stopgaps:
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Comment (by nbruin):
Replying to [comment:9 SimonKing]:
> And have we actually established that this problem does not occur with
older Singular versions?
Quoting from comment:1
>>I have tried and the problem seems to persist with the old singular
(5.4b0 has a recently upgraded singular).
In the mean time, a bit of googling led me to OSX's "GuardMalloc". While
sage+`singular-malloc` does not crash on the doctest, it does crash when
run with
{{{
export DYLD_INSERT_LIBRARIES=/usr/lib/libgmalloc.dylib
}}}
Since gmalloc is a memory manager that places each allocation on its own
page with protected/unmapped memory as close as possible around the block
and that unmaps the block as soon as freed (I'm just parroting the
manpage), a segfault is likely due to an access-after-free or access-out-
of-bounds -- the one that would normally cause the corruption and then the
segfault much later. (that's the whole idea of replacing omalloc -- I
don't think it's doable to get omalloc to segfault on an access-after-
free). This all comes at a significant speed penalty of course, so
experiments are painful and I wouldn't even be able to interpret the
backtrace/coredump if I got it (I'd hope that the gmalloc-induced segfault
would be reproducible in gdb). It would really be useful if the test file
would be pared down to an absolute minimum. That's basically just a
backtracking search on which elements can be removed while still
triggering a segfault.
However, I think this is a strong indication that there is a real memory
violation at the base of this and that it is tracable.
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/13447#comment:10>
Sage <http://www.sagemath.org>
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