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Autoconf Macro: ax_check_page_aligned_malloc
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<h1>
ax_check_page_aligned_malloc
</h1>
<h2>
SYNOPSIS
</h2>
<p class="indent" style="white-space:nowrap;">
<code>AX_CHECK_PAGE_ALIGNED_MALLOC</code>
</p>
<h2>
DESCRIPTION
</h2>
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<p>
Some operating systems (generally, BSD Unix variants) lack a posix_memalign
function, a memalign function, and a working (meaning, the memory can be
freed) valloc function. To make up for it, the malloc function promises to
return page-aligned addresses if more than one page's worth of memory is
allocated. AX_CHECK_PAGE_ALIGNED_MALLOC checks for this condition and
defines HAVE_PAGE_ALIGNED_MALLOC if the condition holds.
</p>
<p>
As an aside, note that valloc'd memory cannot safely be freed on all
operating systems. (Again, some flavors of BSD are the troublemakers.) It's
best to avoid using valloc in favor of posix_memalign, memalign, or an
aligned malloc as detected by AX_CHECK_PAGE_ALIGNED_MALLOC.
</p>
<p>
Caveat: AX_CHECK_PAGE_ALIGNED_MALLOC takes a probabalistic approach. If 100
calls to malloc all return page-aligned addresses, it assumes that all
calls will behave likewise. It is therefore possible -- albeit extremely
unlikely -- that AX_CHECK_PAGE_ALIGNED_MALLOC can return a false positive.
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<h2>
SOURCE CODE
</h2>
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<a href=
"http://autoconf-archive.cryp.to/ax_check_page_aligned_malloc.m4">http://autoconf-archive.cryp.to/ax_check_page_aligned_malloc.m4</a>
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<h2>
LICENSE
</h2>
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Copyright © 2008 Scott Pakin <pakin@uiuc.edu>
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Copying and distribution of this file, with or without modification, are
permitted in any medium without royalty provided the copyright notice and
this notice are preserved.
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