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71 lines
2.4 KiB
Plaintext
Executable File
71 lines
2.4 KiB
Plaintext
Executable File
# =================================================================================
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# https://www.gnu.org/software/autoconf-archive/ax_check_page_aligned_malloc.html
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# =================================================================================
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#
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# SYNOPSIS
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#
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# AX_CHECK_PAGE_ALIGNED_MALLOC
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#
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# DESCRIPTION
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#
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# Some operating systems (generally, BSD Unix variants) lack a
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# posix_memalign function, a memalign function, and a working (meaning,
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# the memory can be freed) valloc function. To make up for it, the malloc
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# function promises to return page-aligned addresses if more than one
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# page's worth of memory is allocated. AX_CHECK_PAGE_ALIGNED_MALLOC checks
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# for this condition and defines HAVE_PAGE_ALIGNED_MALLOC if the condition
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# holds.
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#
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# As an aside, note that valloc'd memory cannot safely be freed on all
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# operating systems. (Again, some flavors of BSD are the troublemakers.)
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# It's best to avoid using valloc in favor of posix_memalign, memalign, or
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# an aligned malloc as detected by AX_CHECK_PAGE_ALIGNED_MALLOC.
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#
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# Caveat: AX_CHECK_PAGE_ALIGNED_MALLOC takes a probabilistic approach. If
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# 100 calls to malloc all return page-aligned addresses, it assumes that
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# all calls will behave likewise. It is therefore possible -- albeit
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# extremely unlikely -- that AX_CHECK_PAGE_ALIGNED_MALLOC can return a
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# false positive.
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#
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# LICENSE
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#
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# Copyright (c) 2008 Scott Pakin <pakin@uiuc.edu>
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#
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# Copying and distribution of this file, with or without modification, are
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# permitted in any medium without royalty provided the copyright notice
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# and this notice are preserved. This file is offered as-is, without any
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# warranty.
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#serial 10
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AC_DEFUN([AX_CHECK_PAGE_ALIGNED_MALLOC],
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[AC_CACHE_CHECK([if large mallocs guarantee page-alignment],
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[ax_cv_func_malloc_aligned],
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[AC_TRY_RUN([
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#include <stdio.h>
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#include <stdlib.h>
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#if HAVE_UNISTD_H
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# include <unistd.h>
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#endif
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int main()
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{
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int pagesize = getpagesize();
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int i;
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for (i=0; i<100; i++)
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if ((unsigned long)malloc(pagesize+1) & (pagesize-1))
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exit (1);
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exit (0);
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}
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],
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[ax_cv_func_malloc_aligned=yes],
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[ax_cv_func_malloc_aligned=no],
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[ax_cv_func_malloc_aligned=no])
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])
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if test "$ax_cv_func_malloc_aligned" = yes ; then
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AC_DEFINE([HAVE_PAGE_ALIGNED_MALLOC], [1],
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[Define if `malloc'ing more than one page always returns a page-aligned address.])
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fi
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])
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