libmmalloc chokes on /dev/zero

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Article #2581

#2581

From: Scott Pakin
Date: Tue, 05 Mar 2002 20:52

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When I use libmmalloc to allocate memory from /dev/zero (e.g., by using
"mmalloc_attach (-1, NULL)" to mmap() it), libmmalloc bus errors when it
tries to write to the allocated region.  The mmalloc library works fine
when I use an ordinary file, however.

I'm using the libmmalloc.a that comes with gdb-5.1, and I'm running under
Linux 2.4.2.  /dev/zero has 0666 permissions.

I believe the bug is that libmmalloc always mmap()s memory with MAP_SHARED,
but it ought to map /dev/zero with MAP_PRIVATE.  A quick search-and-replace
does seem to fix the problem.  I'm guessing that a clean solution
(selecting MAP_SHARED or MAP_PRIVATE based on whether /dev/zero is being
used) should take <10 lines of code.  However, before doing this and
submitting a patch file, I was wondering if there's some subtle reason
the code was written the way it was -- or if I'm the only one who's had
trouble with /dev/zero.

Comments?

-- Scott

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From: pakin@uiuc.edu (Scott Pakin)
Subject: libmmalloc chokes on /dev/zero
Date: Tue, 05 Mar 2002 13:52:58 -0700
Organization: University of Illinois at Urbana-Champaign
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