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Diffstat (limited to 'm4/ax_check_aligned_access_required.m4')
| -rw-r--r-- | m4/ax_check_aligned_access_required.m4 | 84 |
1 files changed, 84 insertions, 0 deletions
diff --git a/m4/ax_check_aligned_access_required.m4 b/m4/ax_check_aligned_access_required.m4 new file mode 100644 index 0000000..b078275 --- /dev/null +++ b/m4/ax_check_aligned_access_required.m4 @@ -0,0 +1,84 @@ +# ==================================================================================== +# http://www.gnu.org/software/autoconf-archive/ax_check_aligned_access_required.html +# ==================================================================================== +# +# SYNOPSIS +# +# AC_CHECK_ALIGNED_ACCESS_REQUIRED +# +# DESCRIPTION +# +# While the x86 CPUs allow access to memory objects to be unaligned it +# happens that most of the modern designs require objects to be aligned - +# or they will fail with a buserror. That mode is quite known by +# big-endian machines (sparc, etc) however the alpha cpu is little- +# endian. +# +# The following function will test for aligned access to be required and +# set a config.h define HAVE_ALIGNED_ACCESS_REQUIRED (name derived by +# standard usage). Structures loaded from a file (or mmapped to memory) +# should be accessed per-byte in that case to avoid segfault type errors. +# +# LICENSE +# +# Copyright (c) 2008 Guido U. Draheim <guidod@gmx.de> +# +# This program is free software; you can redistribute it and/or modify it +# under the terms of the GNU General Public License as published by the +# Free Software Foundation; either version 3 of the License, or (at your +# option) any later version. +# +# This program is distributed in the hope that it will be useful, but +# WITHOUT ANY WARRANTY; without even the implied warranty of +# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General +# Public License for more details. +# +# You should have received a copy of the GNU General Public License along +# with this program. If not, see <http://www.gnu.org/licenses/>. +# +# As a special exception, the respective Autoconf Macro's copyright owner +# gives unlimited permission to copy, distribute and modify the configure +# scripts that are the output of Autoconf when processing the Macro. You +# need not follow the terms of the GNU General Public License when using +# or distributing such scripts, even though portions of the text of the +# Macro appear in them. The GNU General Public License (GPL) does govern +# all other use of the material that constitutes the Autoconf Macro. +# +# This special exception to the GPL applies to versions of the Autoconf +# Macro released by the Autoconf Archive. When you make and distribute a +# modified version of the Autoconf Macro, you may extend this special +# exception to the GPL to apply to your modified version as well. + +#serial 7 + +AC_DEFUN([AX_CHECK_ALIGNED_ACCESS_REQUIRED], +[AC_CACHE_CHECK([if pointers to integers require aligned access], + [ax_cv_have_aligned_access_required], + [AC_TRY_RUN([ +#include <stdio.h> +#include <stdlib.h> + +int main() +{ + char* string = malloc(40); + int i; + for (i=0; i < 40; i++) string[[i]] = i; + { + void* s = string; + int* p = s+1; + int* q = s+2; + + if (*p == *q) { return 1; } + } + return 0; +} + ], + [ax_cv_have_aligned_access_required=yes], + [ax_cv_have_aligned_access_required=no], + [ax_cv_have_aligned_access_required=no]) + ]) +if test "$ax_cv_have_aligned_access_required" = yes ; then + AC_DEFINE([HAVE_ALIGNED_ACCESS_REQUIRED], [1], + [Define if pointers to integers require aligned access]) +fi +]) |