Make it right to check/implement va_copy

configure.ac

@@ -88,7 +88,39 @@ AX_VALGRIND_CHECK
 
 AC_SEARCH_LIBS([socket], [network socket])
 AC_CHECK_FUNCS([snprintf vsnprintf], [], [have_snprintf=no])
-AC_CHECK_DECLS([va_copy], [], [], [#include <stdarg.h>])
+
+dnl Checking for va_copy availability
+AC_MSG_CHECKING([for va_copy])
+AC_LINK_IFELSE([AC_LANG_PROGRAM([[#include <stdarg.h>
+va_list ap1,ap2;]], [[va_copy(ap1,ap2);]])],
+have_va_copy=yes,
+have_va_copy=no)
+AC_MSG_RESULT($have_va_copy)
+if test x"$have_va_copy" = x"yes"; then
+    AC_DEFINE(HAVE_VA_COPY,1,[Whether va_copy() is available])
+else
+    AC_MSG_CHECKING([for __va_copy])
+    AC_LINK_IFELSE([AC_LANG_PROGRAM([[#include <stdarg.h>
+    va_list ap1,ap2;]], [[__va_copy(ap1,ap2);]])],
+    have___va_copy=yes,
+    have___va_copy=no)
+    AC_MSG_RESULT($have___va_copy)
+    if test x"$have___va_copy" = x"yes"; then
+        AC_DEFINE(HAVE___VA_COPY,1,[Whether __va_copy() is available])
+    fi
+fi
+
+if test x"$have_va_copy$have___va_copy" = x"nono"; then
+    dnl Checking whether va_list is an array type
+    AC_MSG_CHECKING([whether va_list is an array type])
+    AC_TRY_COMPILE2([
+    #include <stdarg.h>
+    void a(va_list * ap) {}],[
+    va_list ap1, ap2; a(&ap1); ap2 = (va_list) ap1],[
+      AC_MSG_RESULT(no)],[
+      AC_MSG_RESULT(yes)
+      AC_DEFINE([VA_LIST_IS_ARRAY], [1],[Define if va_list is an array type])])
+fi
 
 if test "x$enable_tls" != xno -a "x$with_gnutls" == xyes; then
     PKG_CHECK_MODULES([gnutls], [gnutls],

m4/ac_try_compile2.m4

@@ -0,0 +1,28 @@
+dnl Like AC_TRY_EVAL but also errors out if the compiler generates
+dnl _any_ output. Some compilers might issue warnings which we want
+dnl to catch.
+AC_DEFUN([AC_TRY_EVAL2],
+[{ (eval echo configure:__oline__: \"[$]$1\") 1>&AS_MESSAGE_LOG_FD; dnl
+(eval [$]$1) 2>&AS_MESSAGE_LOG_FD; _out=`eval [$]$1 2>&1` && test "x$_out" = x; }])
+
+dnl Like AC_TRY_COMPILE but calls AC_TRY_EVAL2 instead of AC_TRY_EVAL
+AC_DEFUN([AC_TRY_COMPILE2],
+[cat > conftest.$ac_ext <<EOF
+[#]line __oline__ "configure"
+#include "confdefs.h"
+[$1]
+int main(void) {
+[$2]
+; return 0; }
+EOF
+if AC_TRY_EVAL2(ac_compile); then
+  ifelse([$3], , :, [rm -rf conftest*
+  $3])
+else
+  echo "configure: failed program was:" >&AS_MESSAGE_LOG_FD
+  cat conftest.$ac_ext >&AS_MESSAGE_LOG_FD
+ifelse([$4], , , [  rm -rf conftest*
+  $4
+])dnl
+fi
+rm -f conftest*])

src/ctx.c

@@ -50,10 +50,22 @@
 #include "resolver.h"
 #include "util.h"
 
-/* Workaround for systems without va_copy support. */
-#if defined(_MSC_VER) && _MSC_VER < 1800 || \
-    !defined(_MSC_VER) && !defined(HAVE_DECL_VA_COPY)
-#define va_copy(d, s) (memcpy(&d, &s, sizeof(va_list)))
+#ifndef va_copy
+#ifdef HAVE_VA_COPY
+#define va_copy(dest, src) va_copy(dest, src)
+#else
+#ifdef HAVE___VA_COPY
+#define va_copy(dest, src) __va_copy(dest, src)
+#else
+#ifndef VA_LIST_IS_ARRAY
+#define va_copy(dest, src) (dest) = (src)
+#else
+#include <string.h>
+#define va_copy(dest, src) \
+    memcpy((char *)(dest), (char *)(src), sizeof(va_list))
+#endif
+#endif
+#endif
 #endif
 
 /** Initialize the Strophe library.