OTP-8323 Miscellaneous cross compilation improvements. For example, one

          new mandatory configuration variable that replaces all other
          previously mandatory configuration variables, and better
          documentation. Note that old cross compilation configurations
          cannot be used without modifications.

          For more information see the $ERL_TOP/xcomp/README file.

README

@@ -243,6 +243,11 @@ if './otp_build remove_prebuilt_files' is invoked.
 If you or your system has special requirements please read the
 Makefile for additional configuration information.
 
+Cross compiling Erlang/OTP
+--------------------------
+The support for cross compiling Erlang/OTP is in its early stage of
+development, and should be considered as experimental. For more
+information see: $ERL_TOP/xcomp/README
 
 How to build a debug enabled Erlang runtime system
 --------------------------------------------------

erts/aclocal.m4

@@ -1,4 +1,4 @@
-
+dnl
 dnl %CopyrightBegin%
 dnl 
 dnl Copyright Ericsson AB 1998-2009. All Rights Reserved.
@@ -15,6 +15,7 @@ dnl the License for the specific language governing rights and limitations
 dnl under the License.
 dnl 
 dnl %CopyrightEnd%
+dnl
 
 dnl
 dnl aclocal.m4
@@ -519,46 +520,79 @@ dnl On ofs1 the '-pthread' switch should be used
 		ETHR_DEFS="$ETHR_DEFS -D_POSIX_PTHREAD_SEMANTICS" ;;
 	    linux*)
 		ETHR_DEFS="$ETHR_DEFS -D_POSIX_THREAD_SAFE_FUNCTIONS -D_GNU_SOURCE"
-		if test "x$erl_xcomp_linux_kernel" != "x"; then
-		    linux_kernel_vsn_=$erl_xcomp_linux_kernel
-		else
-		    linux_kernel_vsn_=`uname -r`
-		fi
-		usable_sigusrx=no
-		usable_sigaltstack=no
 
-		# FIXME: Test for actual problems instead of kernel versions.
-		case $linux_kernel_vsn_ in
-		    [[0-1]].*|2.[[0-1]]|2.[[0-1]].*)
-			;;
-		    2.[[2-3]]|2.[[2-3]].*)
-			usable_sigusrx=yes
-			;;
-		    *)
+		if test	X$cross_compiling = Xyes; then
+		    if test "X$erl_xcomp_linux_usable_sigusrx" = "X"; then
 			usable_sigusrx=yes
+			usable_sigusrx_guessed=yes
+		    else
+			usable_sigusrx=$erl_xcomp_linux_usable_sigusrx
+			usable_sigusrx_guessed=no
+		    fi
+		    if test "X$erl_xcomp_linux_usable_sigaltstack" = "X"; then
 			usable_sigaltstack=yes
-			;;
-		esac
+			usable_sigaltstack_guessed=yes
+		    else
+			usable_sigaltstack=$erl_xcomp_linux_usable_sigaltstack
+			usable_sigaltstack_guessed=no
+		    fi
+		else
+		    # FIXME: Test for actual problems instead of kernel versions
+		    linux_kernel_vsn_=`uname -r`
+		    case $linux_kernel_vsn_ in
+			[[0-1]].*|2.[[0-1]]|2.[[0-1]].*)
+			    usable_sigusrx=no
+			    usable_sigaltstack=no;;
+			2.[[2-3]]|2.[[2-3]].*)
+			    usable_sigusrx=yes
+			    usable_sigaltstack=no;;
+		    	*)
+			    usable_sigusrx=yes
+			    usable_sigaltstack=yes;;
+		    esac
+		    usable_sigusrx_guessed=no
+		    usable_sigaltstack_guessed=no
+		fi
 
 		AC_MSG_CHECKING(if SIGUSR1 and SIGUSR2 can be used)
 		AC_MSG_RESULT($usable_sigusrx)
+		if test $usable_sigusrx_guessed = yes; then
+		    AC_MSG_WARN([result $usable_sigusrx guessed because of cross compilation])
+		fi
 		if test $usable_sigusrx = no; then
 		    ETHR_DEFS="$ETHR_DEFS -DETHR_UNUSABLE_SIGUSRX"
 		fi
 
 		AC_MSG_CHECKING(if sigaltstack can be used)
 		AC_MSG_RESULT($usable_sigaltstack)
+		if test $usable_sigaltstack_guessed = yes; then
+		    AC_MSG_WARN([result $usable_sigaltstack guessed because of cross compilation])
+		fi
 		if test $usable_sigaltstack = no; then
 		    ETHR_DEFS="$ETHR_DEFS -DETHR_UNUSABLE_SIGALTSTACK"
 		fi
 
 		AC_MSG_CHECKING(for Native POSIX Thread Library)
-		case `getconf GNU_LIBPTHREAD_VERSION 2>/dev/null` in
-		    nptl*) nptl=yes;;
-		    NPTL*) nptl=yes;;
-		    *)  nptl=no;;
-		esac
+		if test	X$cross_compiling = Xyes; then
+		    if test "X$erl_xcomp_linux_nptl" = "X"; then
+			nptl=yes
+			nptl_guessed=yes
+		    else
+			nptl=$erl_xcomp_linux_nptl
+			nptl_guessed=no
+		    fi
+		else
+		    case `getconf GNU_LIBPTHREAD_VERSION 2>/dev/null` in
+			nptl*) nptl=yes;;
+			NPTL*) nptl=yes;;
+			*)  nptl=no;;
+		    esac
+		    nptl_guessed=no
+		fi
 		AC_MSG_RESULT($nptl)
+		if test $nptl_guessed = yes; then
+		    AC_MSG_WARN([result $nptl guessed because of cross compilation])
+		fi
 		if test $nptl = yes; then
 		    ETHR_THR_LIB_BASE_NAME=nptl
 		fi
@@ -567,7 +601,10 @@ dnl On ofs1 the '-pthread' switch should be used
 		    AC_CHECK_HEADER(nptl/pthread.h, need_nptl_incldir=yes)
 		    if test $need_nptl_incldir = yes; then
 			# Ahh...
-			nptl_path="$C_INCLUDE_PATH:$CPATH:/usr/local/include:/usr/include"
+			nptl_path="$C_INCLUDE_PATH:$CPATH"
+			if test X$cross_compiling != Xyes; then
+			    nptl_path="$nptl_path:/usr/local/include:/usr/include"
+			fi
 			nptl_ws_path=
 			save_ifs="$IFS"; IFS=":"
 			for dir in $nptl_path; do
@@ -683,7 +720,7 @@ if test "x$ETHR_THR_LIB_BASE" != "x"; then
 	ETHR_LIB_NAME=$ethr_lib_name
 fi
 
-AC_CHECK_SIZEOF(void *, 4)
+AC_CHECK_SIZEOF(void *)
 AC_DEFINE_UNQUOTED(ETHR_SIZEOF_PTR, $ac_cv_sizeof_void_p, [Define to the size of pointers])
 
 if test "X$disable_native_ethr_impls" = "Xyes"; then
@@ -751,13 +788,21 @@ case $clock_gettime_correction in
 			case $clock_gettime_correction in
 			    unknown)
 				if test x$clock_gettime_compiles = xyes; then
-				    linux_kernel_vsn_=`uname -r`
-				    case $linux_kernel_vsn_ in
-					[[0-1]].*|2.[[0-5]]|2.[[0-5]].*)
-					    erl_cv_time_correction=times ;;
-					*)
-					    erl_cv_time_correction=clock_gettime;;
-				    esac
+				    if test X$cross_compiling != Xyes; then
+					if test "X$erl_xcomp_linux_clock_gettime_correction" = "Xno"; then
+					    erl_cv_time_correction=times
+					else
+					    erl_cv_time_correction=clock_gettime
+					fi
+				    else
+				    	linux_kernel_vsn_=`uname -r`
+				    	case $linux_kernel_vsn_ in
+					    [[0-1]].*|2.[[0-5]]|2.[[0-5]].*)
+					    	erl_cv_time_correction=times ;;
+					    *)
+					    	erl_cv_time_correction=clock_gettime;;
+				    	esac
+				    fi
 				else
 				    erl_cv_time_correction=times
 				fi
@@ -774,13 +819,17 @@ case $clock_gettime_correction in
 	;;
 esac
 ])
+
 xrtlib=""
 case $erl_cv_time_correction in
   times)
     AC_DEFINE(CORRECT_USING_TIMES,[],
 	[Define if you do not have a high-res. timer & want to use times() instead])
     ;;
   clock_gettime)
+    if test X$cross_compiling = Xyes -a X$erl_xcomp_linux_clock_gettime_correction = X; then
+	AC_MSG_WARN([result clock_gettime guessed because of cross compilation])
+    fi
     xrtlib="-lrt"
     AC_DEFINE(GETHRTIME_WITH_CLOCK_GETTIME,[1],
 	[Define if you want to use clock_gettime to simulate gethrtime])
@@ -840,7 +889,15 @@ int main() {
 	exit(5);
     exit(0); return 0;
 }
-], erl_gethrvtime=procfs_ioctl, erl_gethrvtime=false, erl_gethrvtime=false)
+],
+erl_gethrvtime=procfs_ioctl,
+erl_gethrvtime=false,
+if test "x$erl_xcomp_gethrvtime_procfs_ioctl" = "xyes"; then
+	erl_gethrvtime=procfs_ioctl
+else
+	erl_gethrvtime=false
+fi)
+
 case $erl_gethrvtime in
   procfs_ioctl)
 	AC_DEFINE(HAVE_GETHRVTIME_PROCFS_IOCTL,[1],
@@ -880,7 +937,14 @@ case $erl_gethrvtime in
 	      exit(5);
 	    exit(0); return 0;
 	  }
-	], erl_clock_gettime=true, erl_clock_gettime=false, erl_clock_gettime=false)
+	],
+	erl_clock_gettime=true,
+	erl_clock_gettime=false,
+	if test "x$erl_xcomp_clock_gettime" = "xyes"; then
+		erl_clock_gettime=true
+	else
+		erl_clock_gettime=false
+	fi)
 	LIBS=$save_libs
 	case $host_os in
 		linux*)