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      1 # woe32-dll.m4 serial 2
      2 dnl Copyright (C) 2005-2006 Free Software Foundation, Inc.
      3 dnl This file is free software; the Free Software Foundation
      4 dnl gives unlimited permission to copy and/or distribute it,
      5 dnl with or without modifications, as long as this notice is preserved.
      6 
      7 dnl From Bruno Haible.
      8 
      9 # Add --disable-auto-import to the LDFLAGS if the linker supports it.
     10 # GNU ld has an --enable-auto-import option, and it is the default on Cygwin
     11 # since July 2005. But it has three fatal drawbacks:
     12 #   - It produces executables and shared libraries with relocations in the
     13 #     .text segment, defeating the principles of virtual memory.
     14 #   - For some constructs such as
     15 #         extern int var;
     16 #         int * const b = &var;
     17 #     it creates an executable that will give an error at runtime, rather
     18 #     than either a compile-time or link-time error or a working executable.
     19 #     (This is with both gcc and g++.) Whereas this code, not relying on
     20 #     auto-import:
     21 #         extern __declspec (dllimport) int var;
     22 #         int * const b = &var;
     23 #     gives a compile-time error with gcc and works with g++.
     24 #   - It doesn't work in some cases (references to a member field of an
     25 #     exported struct variable, or to a particular element of an exported
     26 #     array variable), requiring code modifications.  One platform
     27 #     dictates code modifications on all platforms.
     28 AC_DEFUN([gl_WOE32_DLL],
     29 [
     30   AC_REQUIRE([AC_CANONICAL_HOST])
     31   case "$host_os" in
     32     mingw* | cygwin*)
     33       AC_MSG_CHECKING([for auto-import of symbols])
     34       AC_CACHE_VAL([gl_cv_ld_autoimport], [
     35         gl_save_LDFLAGS="$LDFLAGS"
     36         LDFLAGS="$LDFLAGS -Wl,--disable-auto-import"
     37         AC_TRY_LINK([], [], [gl_cv_ld_autoimport=yes], [gl_cv_ld_autoimport=no])
     38         LDFLAGS="$gl_save_LDFLAGS"])
     39       AC_MSG_RESULT([$gl_cv_ld_autoimport])
     40       if test $gl_cv_ld_autoimport = yes; then
     41         LDFLAGS="$LDFLAGS -Wl,--disable-auto-import"
     42       fi
     43       ;;
     44   esac
     45 ])
     46