1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
|
# =====================================================================================
# https://www.gnu.org/software/autoconf-archive/ax_check_aligned_access_required.html
# =====================================================================================
#
# SYNOPSIS
#
# AX_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.
#
# The function checks if unaligned access would ignore the lowest bit of
# the address. If that happens or if the test binary crashes, aligned
# access is required.
#
# If cross-compiling, assume that aligned access is needed to be safe. Set
# ax_cv_have_aligned_access_required=no to override that assumption.
#
# LICENSE
#
# Copyright (c) 2008 Guido U. Draheim <guidod@gmx.de>
#
# 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.
#serial 11
AC_DEFUN([AX_CHECK_ALIGNED_ACCESS_REQUIRED],
[AC_CACHE_CHECK([if pointers to integers require aligned access],
[ax_cv_have_aligned_access_required],
[AC_RUN_IFELSE([
AC_LANG_PROGRAM([[@%:@include <stdlib.h>]],
[[
int i;
int *p;
int *q;
char *str;
str = (char *) malloc(40);
for (i = 0; i < 40; i++) {
*(str + i) = i;
}
p = (int *) (str + 1);
q = (int *) (str + 2);
return (*p == *q);
]])],
[ax_cv_have_aligned_access_required=no],
[ax_cv_have_aligned_access_required=yes],
[ax_cv_have_aligned_access_required=maybe])])
if test "x$ax_cv_have_aligned_access_required" = "xmaybe"; then
AC_MSG_WARN([Assuming aligned access is required when cross-compiling])
ax_cv_have_aligned_access_required=yes
fi
if test "x$ax_cv_have_aligned_access_required" = "xyes"; then
AC_DEFINE([HAVE_ALIGNED_ACCESS_REQUIRED], [1],
[Define if pointers to integers require aligned access])
fi
])
|
