| # memchr.m4 serial 12 |
| dnl Copyright (C) 2002-2004, 2009-2016 Free Software Foundation, Inc. |
| dnl This file is free software; the Free Software Foundation |
| dnl gives unlimited permission to copy and/or distribute it, |
| dnl with or without modifications, as long as this notice is preserved. |
| |
| AC_DEFUN_ONCE([gl_FUNC_MEMCHR], |
| [ |
| dnl Check for prerequisites for memory fence checks. |
| gl_FUNC_MMAP_ANON |
| AC_CHECK_HEADERS_ONCE([sys/mman.h]) |
| AC_CHECK_FUNCS_ONCE([mprotect]) |
| |
| AC_REQUIRE([gl_HEADER_STRING_H_DEFAULTS]) |
| m4_ifdef([gl_FUNC_MEMCHR_OBSOLETE], [ |
| dnl These days, we assume memchr is present. But if support for old |
| dnl platforms is desired: |
| AC_CHECK_FUNCS_ONCE([memchr]) |
| if test $ac_cv_func_memchr = no; then |
| HAVE_MEMCHR=0 |
| fi |
| ]) |
| if test $HAVE_MEMCHR = 1; then |
| # Detect platform-specific bugs in some versions of glibc: |
| # memchr should not dereference anything with length 0 |
| # http://bugzilla.redhat.com/499689 |
| # memchr should not dereference overestimated length after a match |
| # http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=521737 |
| # http://sourceware.org/bugzilla/show_bug.cgi?id=10162 |
| # Assume that memchr works on platforms that lack mprotect. |
| AC_CACHE_CHECK([whether memchr works], [gl_cv_func_memchr_works], |
| [AC_RUN_IFELSE([AC_LANG_PROGRAM([[ |
| #include <string.h> |
| #if HAVE_SYS_MMAN_H |
| # include <fcntl.h> |
| # include <unistd.h> |
| # include <sys/types.h> |
| # include <sys/mman.h> |
| # ifndef MAP_FILE |
| # define MAP_FILE 0 |
| # endif |
| #endif |
| ]], [[ |
| int result = 0; |
| char *fence = NULL; |
| #if HAVE_SYS_MMAN_H && HAVE_MPROTECT |
| # if HAVE_MAP_ANONYMOUS |
| const int flags = MAP_ANONYMOUS | MAP_PRIVATE; |
| const int fd = -1; |
| # else /* !HAVE_MAP_ANONYMOUS */ |
| const int flags = MAP_FILE | MAP_PRIVATE; |
| int fd = open ("/dev/zero", O_RDONLY, 0666); |
| if (fd >= 0) |
| # endif |
| { |
| int pagesize = getpagesize (); |
| char *two_pages = |
| (char *) mmap (NULL, 2 * pagesize, PROT_READ | PROT_WRITE, |
| flags, fd, 0); |
| if (two_pages != (char *)(-1) |
| && mprotect (two_pages + pagesize, pagesize, PROT_NONE) == 0) |
| fence = two_pages + pagesize; |
| } |
| #endif |
| if (fence) |
| { |
| if (memchr (fence, 0, 0)) |
| result |= 1; |
| strcpy (fence - 9, "12345678"); |
| if (memchr (fence - 9, 0, 79) != fence - 1) |
| result |= 2; |
| if (memchr (fence - 1, 0, 3) != fence - 1) |
| result |= 4; |
| } |
| return result; |
| ]])], [gl_cv_func_memchr_works=yes], [gl_cv_func_memchr_works=no], |
| [dnl Be pessimistic for now. |
| gl_cv_func_memchr_works="guessing no"])]) |
| if test "$gl_cv_func_memchr_works" != yes; then |
| REPLACE_MEMCHR=1 |
| fi |
| fi |
| ]) |
| |
| # Prerequisites of lib/memchr.c. |
| AC_DEFUN([gl_PREREQ_MEMCHR], [ |
| AC_CHECK_HEADERS([bp-sym.h]) |
| ]) |