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ax_check_page_aligned_malloc

Synopsis

AX_CHECK_PAGE_ALIGNED_MALLOC

Description

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.

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.

Caveat: AX_CHECK_PAGE_ALIGNED_MALLOC takes a probabilistic 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.

Source Code

Download the latest version of ax_check_page_aligned_malloc.m4 or browse the macro’s revision history.

License

Copyright © 2008 Scott Pakin pakin@uiuc.edu

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. This file is offered as-is, without any warranty.