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1 # memchr.m4 serial 7
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2 dnl Copyright (C) 2002-2004, 2009-2010 Free Software Foundation, Inc.
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3 dnl This file is free software; the Free Software Foundation
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4 dnl gives unlimited permission to copy and/or distribute it,
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5 dnl with or without modifications, as long as this notice is preserved.
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6
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7 AC_DEFUN_ONCE([gl_FUNC_MEMCHR],
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8 [
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9 dnl Check for prerequisites for memory fence checks.
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10 gl_FUNC_MMAP_ANON
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11 AC_CHECK_HEADERS_ONCE([sys/mman.h])
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12 AC_CHECK_FUNCS_ONCE([mprotect])
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13
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14 dnl These days, we assume memchr is present. But just in case...
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15 AC_REQUIRE([gl_HEADER_STRING_H_DEFAULTS])
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16 AC_REPLACE_FUNCS([memchr])
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17 if test $ac_cv_func_memchr = no; then
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18 gl_PREREQ_MEMCHR
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19 REPLACE_MEMCHR=1
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20 fi
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21
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22 if test $ac_cv_func_memchr = yes; then
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23 # Detect platform-specific bugs in some versions of glibc:
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24 # memchr should not dereference anything with length 0
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25 # http://bugzilla.redhat.com/499689
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26 # memchr should not dereference overestimated length after a match
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27 # http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=521737
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28 # http://sourceware.org/bugzilla/show_bug.cgi?id=10162
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29 # Assume that memchr works on platforms that lack mprotect.
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30 AC_CACHE_CHECK([whether memchr works], [gl_cv_func_memchr_works],
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31 [AC_RUN_IFELSE([AC_LANG_PROGRAM([[
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32 #include <string.h>
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33 #if HAVE_SYS_MMAN_H
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34 # include <fcntl.h>
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35 # include <unistd.h>
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36 # include <sys/types.h>
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37 # include <sys/mman.h>
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38 # ifndef MAP_FILE
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39 # define MAP_FILE 0
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40 # endif
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41 #endif
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42 ]], [[
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43 char *fence = NULL;
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44 #if HAVE_SYS_MMAN_H && HAVE_MPROTECT
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45 # if HAVE_MAP_ANONYMOUS
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46 const int flags = MAP_ANONYMOUS | MAP_PRIVATE;
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47 const int fd = -1;
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48 # else /* !HAVE_MAP_ANONYMOUS */
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49 const int flags = MAP_FILE | MAP_PRIVATE;
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50 int fd = open ("/dev/zero", O_RDONLY, 0666);
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51 if (fd >= 0)
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52 # endif
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53 {
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54 int pagesize = getpagesize ();
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55 char *two_pages =
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56 (char *) mmap (NULL, 2 * pagesize, PROT_READ | PROT_WRITE,
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57 flags, fd, 0);
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58 if (two_pages != (char *)(-1)
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59 && mprotect (two_pages + pagesize, pagesize, PROT_NONE) == 0)
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60 fence = two_pages + pagesize;
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61 }
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62 #endif
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63 if (fence)
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64 {
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65 if (memchr (fence, 0, 0))
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66 return 1;
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67 strcpy (fence - 9, "12345678");
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68 if (memchr (fence - 9, 0, 79) != fence - 1)
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69 return 2;
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70 }
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71 return 0;
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72 ]])], [gl_cv_func_memchr_works=yes], [gl_cv_func_memchr_works=no],
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73 [dnl Be pessimistic for now.
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74 gl_cv_func_memchr_works="guessing no"])])
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75 if test "$gl_cv_func_memchr_works" != yes; then
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76 gl_PREREQ_MEMCHR
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77 REPLACE_MEMCHR=1
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78 AC_LIBOBJ([memchr])
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79 fi
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80 fi
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81 ])
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82
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83 # Prerequisites of lib/memchr.c.
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84 AC_DEFUN([gl_PREREQ_MEMCHR], [
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85 AC_CHECK_HEADERS([bp-sym.h])
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86 ])
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