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# woe32-dll.m4 serial 6
dnl Copyright (C) 2005-2006, 2011, 2018, 2020 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.
dnl From Bruno Haible.
# Add --disable-auto-import to the LDFLAGS if the linker supports it.
# GNU ld has an --enable-auto-import option, and it is the default on Cygwin
# since July 2005. But it has three fatal drawbacks:
# - It produces executables and shared libraries with relocations in the
# .text segment, defeating the principles of virtual memory.
# - For some constructs such as
# extern int var;
# int * const b = &var;
# it creates an executable that will give an error at runtime, rather
# than either a compile-time or link-time error or a working executable.
# (This is with both gcc and g++.) Whereas this code, not relying on
# auto-import:
# extern __declspec (dllimport) int var;
# int * const b = &var;
# gives a compile-time error with gcc and works with g++.
# - It doesn't work in some cases (references to a member field of an
# exported struct variable, or to a particular element of an exported
# array variable), requiring code modifications. One platform
# dictates code modifications on all platforms.
# See <https://haible.de/bruno/woe32dll.html> for more details.
AC_DEFUN([gl_WOE32_DLL],
[
AC_REQUIRE([AC_CANONICAL_HOST])
case "$host_os" in
mingw* | cygwin*)
AC_CACHE_CHECK([for auto-import of symbols],
[gl_cv_ld_autoimport],
[dnl --disable-auto-import is unsupported in MSVC and in MSVC/clang.
dnl We need to sort out this case explicitly, because with clang,
dnl -Wl,--disable-auto-import does not yield an error, however later
dnl libtool turns it into --disable-auto-import, which does produce
dnl an error.
AC_EGREP_CPP([Known], [
#ifdef _MSC_VER
Known
#endif
],
[gl_cv_ld_autoimport=no],
[gl_save_LDFLAGS="$LDFLAGS"
LDFLAGS="$LDFLAGS -Wl,--disable-auto-import"
AC_LINK_IFELSE([], [gl_cv_ld_autoimport=yes], [gl_cv_ld_autoimport=no])
LDFLAGS="$gl_save_LDFLAGS"
])
])
if test $gl_cv_ld_autoimport = yes; then
LDFLAGS="$LDFLAGS -Wl,--disable-auto-import"
fi
;;
esac
])
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