Raspberry PI / Android a minimal cross-compile configuration

Enable a cross compile Erlang/OTP platform to Android or Raspberry PI
using Android NDK. Port emulator and core application to support target
HW platform. Exclude any add-on services required for OTP platform deployment
into target hardware due to device fragmentation and jail-break requirements.

 * fix erts/emulator/beam/sys.h
   Disable redefinition of __noreturn macro

 * port erts/emulator/sys/unix/erl_child_setup.c
   Use techniques proposed by https://code.google.com/p/erlang4android to
   access system properties

 * fix erts/emulator/sys/unix/erl_unix_sys_ddll.c
   The static linking of emulator cannot find dlerror(), dlopen() symbols

 * port erts/emulator/sys/unix/sys.c
   make path to shell configurable at build time

 * port erts/etc/common/Makefile.in
   disable librt for *-linux-androideabi

 * port erts/lib_src/pthread/ethread.c
   Use techniques proposed by https://code.google.com/p/erlang4android to
   disable emulator crash if kernel threads are on. Replace unreliable
   pthread_sigmask() by sigprocmask()

 * port lib/erl_interface/src/connect/ei_connect.c
   Disable call to undefined gethostid()

 * port lib/erl_interface/src/connect/ei_resolve.c
   Use gethostbyname_r() on Android platform

13 files changed, 401 insertions, 10 deletions

diff --git a/HOWTO/INSTALL-ANDROID.md b/HOWTO/INSTALL-ANDROID.md
new file mode 100644
index 0000000000..31698d4ce3
--- /dev/null
+++ b/HOWTO/INSTALL-ANDROID.md
@@ -0,0 +1,52 @@
+Cross Compiling Erlang/OTP - ANDROID
+====================================
+
+Introduction
+------------
+
+This document describes how to cross compile Erlang OTP to Android/Rasberry Pi platforms.
+
+### Download and Install Android NDK ###
+
+https://developer.android.com/tools/sdk/ndk/index.html
+
+### Define System Variables ###
+
+export NDK_ROOT=/usr/local/android
+export NDK_PLAT=android-9
+export PATH=$NDK_ROOT/toolchains/arm-linux-androideabi-4.8/prebuilt/darwin-x86_64/bin:$PATH
+
+### Configure OTP ###
+
+./otp_build configure \
+   --xcomp-conf=./xcomp/erl-xcomp-arm-android.conf  \
+   --without-ssl
+
+### Compile OTP ###
+
+make noboot [-j4]
+
+### Make Release ###
+
+./otp_build release -a /usr/local/otp_R16B03_arm
+
+### Target Deployment ###
+
+Make a tarball out of /usr/local/otp_R16B03_arm and copy it to target device
+(e.g. Raspberry Pi). Extract it and install
+
+./Install /usr/local/otp_R16B03_arm
+
+Android SDK (adb tool) is used to deploy OTP/Erlang to target device for 
+evaluation purpose only.
+
+adb push /usr/local/otp_R16B03_arm /mnt/sdcard/otp_R16B03_arm
+adb shell
+
+### Known Issues ###
+
+ * native inet:gethostbyname/1 return {error, nxdomain} on Raspberry PI. Use dns resolver to by-pass the issue (see http://www.erlang.org/doc/apps/erts/inet_cfg.html) 
+
+### References ###
+
+  The port derives some solutions from https://code.google.com/p/erlang4android/
diff --git a/erts/emulator/Makefile.in b/erts/emulator/Makefile.in
index 2a9a0a5c2f..58e77ed1fa 100644
--- a/erts/emulator/Makefile.in
+++ b/erts/emulator/Makefile.in
@@ -378,7 +378,9 @@ LIBS += -l$(ERTS_INTERNAL_LIB)$(TYPEMARKER)
 
 endif # erts_internal_r
 
+ifneq ($(TARGET),arm-unknown-linux-androideabi)
 LIBS += @LIBRT@
+endif
 
 LIBS += @LIBCARBON@
 
diff --git a/erts/emulator/beam/sys.h b/erts/emulator/beam/sys.h
index e273056a2b..05f07e57b2 100644
--- a/erts/emulator/beam/sys.h
+++ b/erts/emulator/beam/sys.h
@@ -154,10 +154,14 @@ typedef ERTS_SYS_FD_TYPE ErtsSysFdType;
 /* In VC++, noreturn is a declspec that has to be before the types,
  * but in GNUC it is an att ribute to be placed between return type
  * and function name, hence __decl_noreturn <types> __noreturn <function name>
+ *
+ * at some platforms (e.g. Android) __noreturn is defined at sys/cdef.h
  */
 #if __GNUC__
 #  define __decl_noreturn
-#  define __noreturn __attribute__((noreturn))
+#  ifndef __noreturn
+#     define __noreturn __attribute__((noreturn))
+#  endif
 #else
 #  if defined(__WIN32__) && defined(_MSC_VER)
 #    define __noreturn
diff --git a/erts/emulator/sys/unix/erl_child_setup.c b/erts/emulator/sys/unix/erl_child_setup.c
index 7c6e4a2f37..34d7f9e0e5 100644
--- a/erts/emulator/sys/unix/erl_child_setup.c
+++ b/erts/emulator/sys/unix/erl_child_setup.c
@@ -54,6 +54,17 @@ void sys_sigrelease(int sig)
 #endif /* !SIG_SIGNAL */
 #endif /* !SIG_SIGSET */
 
+#if defined(__ANDROID__)
+int __system_properties_fd(void);
+#endif /* __ANDROID__ */
+
+#if defined(__ANDROID__)
+#define SHELL "/system/bin/sh"
+#else
+#define SHELL "/bin/sh"
+#endif /* __ANDROID__ */
+
+
 int
 main(int argc, char *argv[])
 {
@@ -89,8 +100,16 @@ main(int argc, char *argv[])
 
     if (sscanf(argv[CS_ARGV_FD_CR_IX], "%d:%d", &from, &to) != 2)
 	return 1;
+
+#if defined(__ANDROID__)
+    for (i = from; i <= to; i++) {
+	if (i!=__system_properties_fd)
+	    (void) close(i);
+    }
+#else
     for (i = from; i <= to; i++)
 	(void) close(i);
+#endif /* __ANDROID__ */
 
     if (!(argv[CS_ARGV_WD_IX][0] == '.' && argv[CS_ARGV_WD_IX][1] == '\0')
 	&& chdir(argv[CS_ARGV_WD_IX]) < 0)
@@ -116,7 +135,25 @@ main(int argc, char *argv[])
 	    execv(argv[CS_ARGV_NO_OF_ARGS],&(argv[CS_ARGV_NO_OF_ARGS + 1]));
 	}
     } else {
-	execl("/bin/sh", "sh", "-c", argv[CS_ARGV_CMD_IX], (char *) NULL);
+        execl(SHELL, "sh", "-c", argv[CS_ARGV_CMD_IX], (char *) NULL);
     }
     return 1;
 }
+
+
+
+#if defined(__ANDROID__)
+int __system_properties_fd(void)
+{
+    int s, fd;
+    char *env;
+
+    env = getenv("ANDROID_PROPERTY_WORKSPACE");
+    if (!env) {
+        return -1;
+    }
+    fd = atoi(env);
+    return fd;
+}
+#endif /* __ANDROID__ */
+
diff --git a/erts/emulator/sys/unix/erl_unix_sys_ddll.c b/erts/emulator/sys/unix/erl_unix_sys_ddll.c
index 8760b58839..2659d623c7 100644
--- a/erts/emulator/sys/unix/erl_unix_sys_ddll.c
+++ b/erts/emulator/sys/unix/erl_unix_sys_ddll.c
@@ -123,6 +123,7 @@ int erts_sys_ddll_open(const char *full_name, void **handle, ErtsSysDdllError* e
 
 int erts_sys_ddll_open_noext(char *dlname, void **handle, ErtsSysDdllError* err)
 {
+#if defined(HAVE_DLOPEN)   
     int ret = ERL_DE_NO_ERROR;
     char *str;
     dlerror();
@@ -148,6 +149,9 @@ int erts_sys_ddll_open_noext(char *dlname, void **handle, ErtsSysDdllError* err)
 	ret = ERL_DE_DYNAMIC_ERROR_OFFSET - find_errcode(str, err);
     }
     return ret;
+#else
+    return ERL_DE_ERROR_NO_DDLL_FUNCTIONALITY;
+#endif
 }
 
 /* 
diff --git a/erts/emulator/sys/unix/sys.c b/erts/emulator/sys/unix/sys.c
index 865cb50a56..c3d7440409 100644
--- a/erts/emulator/sys/unix/sys.c
+++ b/erts/emulator/sys/unix/sys.c
@@ -149,6 +149,13 @@ extern void erl_crash_dump(char* file, int line, char* fmt, ...);
 
 #define DIR_SEPARATOR_CHAR    '/'
 
+#if defined(__ANDROID__)
+#define SHELL "/system/bin/sh"
+#else
+#define SHELL "/bin/sh"
+#endif /* __ANDROID__ */
+
+
 #if defined(DEBUG)
 #define ERL_BUILD_TYPE_MARKER ".debug"
 #elif defined(PURIFY)
@@ -1596,7 +1603,7 @@ static ErlDrvData spawn_start(ErlDrvPort port_num, char* name, SysDriverOpts* op
 		    }
 		}
 	    } else {
-		execle("/bin/sh", "sh", "-c", cmd_line, (char *) NULL, new_environ);
+		execle(SHELL, "sh", "-c", cmd_line, (char *) NULL, new_environ);
 	    }
 	child_error:
 	    _exit(1);
@@ -1717,7 +1724,7 @@ static ErlDrvData spawn_start(ErlDrvPort port_num, char* name, SysDriverOpts* op
 	fcntl(i, F_SETFD, 1);
 
     qnx_spawn_options.flags = _SPAWN_SETSID;
-    if ((pid = spawnl(P_NOWAIT, "/bin/sh", "/bin/sh", "-c", cmd_line, 
+    if ((pid = spawnl(P_NOWAIT, SHELL, SHELL, "-c", cmd_line, 
                       (char *) 0)) < 0) {
 	erts_free(ERTS_ALC_T_TMP, (void *) cmd_line);
         reset_qnx_spawn();
diff --git a/erts/etc/common/Makefile.in b/erts/etc/common/Makefile.in
index 5c2cd8aded..cfd36af962 100644
--- a/erts/etc/common/Makefile.in
+++ b/erts/etc/common/Makefile.in
@@ -66,7 +66,9 @@ LIBS      = @LIBS@
 LDFLAGS   = @LDFLAGS@
 
 # For clock_gettime in heart
+ifneq ($(TARGET),arm-unknown-linux-androideabi)
 RTLIBS = @LIBRT@
+endif
 
 ifeq ($(TARGET),win32)
 ifeq ($(TYPE),debug)
diff --git a/erts/lib_src/pthread/ethread.c b/erts/lib_src/pthread/ethread.c
index 7f27b5f29c..79784c5b84 100644
--- a/erts/lib_src/pthread/ethread.c
+++ b/erts/lib_src/pthread/ethread.c
@@ -541,7 +541,11 @@ int ethr_sigmask(int how, const sigset_t *set, sigset_t *oset)
 	return EINVAL;
     }
 #endif
-  return pthread_sigmask(how, set, oset);
+#if defined(__ANDROID__)
+   return sigprocmask(how, set, oset);
+#else 
+   return pthread_sigmask(how, set, oset);
+#endif    
 }
 
 int ethr_sigwait(const sigset_t *set, int *sig)
diff --git a/lib/erl_interface/src/connect/ei_connect.c b/lib/erl_interface/src/connect/ei_connect.c
index 3175d1bdfd..2e8418d61e 100644
--- a/lib/erl_interface/src/connect/ei_connect.c
+++ b/lib/erl_interface/src/connect/ei_connect.c
@@ -1166,7 +1166,11 @@ static unsigned int gen_challenge(void)
     uname(&s.name);
     s.cpu  = clock();
     s.pid  = getpid();
+#ifndef __ANDROID__
     s.hid  = gethostid();
+#else
+    s.hid  = 0;
+#endif
     s.uid  = getuid();
     s.gid  = getgid();
 
diff --git a/lib/erl_interface/src/connect/ei_resolve.c b/lib/erl_interface/src/connect/ei_resolve.c
index 74dcba61a7..cffcac801c 100644
--- a/lib/erl_interface/src/connect/ei_resolve.c
+++ b/lib/erl_interface/src/connect/ei_resolve.c
@@ -642,7 +642,7 @@ struct hostent *ei_gethostbyname_r(const char *name,
 #ifndef HAVE_GETHOSTBYNAME_R
   return my_gethostbyname_r(name,hostp,buffer,buflen,h_errnop);
 #else
-#if (defined(__GLIBC__) || (__FreeBSD_version >= 602000) || defined(__DragonFly__))
+#if (defined(__GLIBC__) || (__FreeBSD_version >= 602000) || defined(__DragonFly__) || defined(__ANDROID__))
   struct hostent *result;
 
   gethostbyname_r(name, hostp, buffer, buflen, &result, h_errnop);
diff --git a/lib/kernel/src/os.erl b/lib/kernel/src/os.erl
index 9ffa9adeab..3bda391b8e 100644
--- a/lib/kernel/src/os.erl
+++ b/lib/kernel/src/os.erl
@@ -230,7 +230,9 @@ unix_cmd(Cmd) ->
 %% and the commands are read from standard input. We set the
 %% $1 parameter for easy identification of the resident shell.
 %%
--define(SHELL, "/bin/sh -s unix:cmd 2>&1").
+-define(ROOT,          "/").
+-define(ROOT_ANDROID,  "/system").
+-define(SHELL, "bin/sh -s unix:cmd 2>&1").
 -define(PORT_CREATOR_NAME, os_cmd_port_creator).
 
 %%
@@ -280,7 +282,12 @@ start_port_srv(Request) ->
     end.
 
 start_port_srv_handle({Ref,Client}) ->
-    Reply = try open_port({spawn, ?SHELL},[stream]) of
+    Path  = case lists:reverse(erlang:system_info(system_architecture)) of
+      % androideabi
+      "ibaediordna" ++ _ -> filename:join([?ROOT_ANDROID, ?SHELL]);
+      _ -> filename:join([?ROOT, ?SHELL])
+    end,
+    Reply = try open_port({spawn, Path},[stream]) of
 		Port when is_port(Port) ->
 		    (catch port_connect(Port, Client)),
 		    unlink(Port),
diff --git a/lib/os_mon/c_src/memsup.c b/lib/os_mon/c_src/memsup.c
index b5114d10ed..409db84aa7 100644
--- a/lib/os_mon/c_src/memsup.c
+++ b/lib/os_mon/c_src/memsup.c
@@ -324,7 +324,7 @@ get_mem_procfs(memory_ext *me){
 
 /* arch specific functions */
 
-#if defined(__linux__) /* ifdef SYSINFO */
+#if defined(__linux__) && !defined(__ANDROID__)/* ifdef SYSINFO */
 /* sysinfo does not include cached memory which is a problem. */
 static int
 get_extended_mem_sysinfo(memory_ext *me) {
@@ -395,8 +395,12 @@ get_extended_mem_sgi(memory_ext *me) {
 
 static void
 get_extended_mem(memory_ext *me) {
+/* android */
+#if defined(__ANDROID__)
+    if (get_mem_procfs(me))  return;   
+
 /* linux */
-#if defined(__linux__)
+#elif defined(__linux__)
     if (get_mem_procfs(me))  return;
     if (get_extended_mem_sysinfo(me)) return;
 
diff --git a/xcomp/erl-xcomp-arm-android.conf b/xcomp/erl-xcomp-arm-android.conf
new file mode 100644
index 0000000000..4fd1f270d1
--- /dev/null
+++ b/xcomp/erl-xcomp-arm-android.conf
@@ -0,0 +1,264 @@
+## -*-shell-script-*-
+##
+## %CopyrightBegin%
+##
+## Copyright Ericsson AB 2009-2010. All Rights Reserved.
+##
+## The contents of this file are subject to the Erlang Public License,
+## Version 1.1, (the "License"); you may not use this file except in
+## compliance with the License. You should have received a copy of the
+## Erlang Public License along with this software. If not, it can be
+## retrieved online at http://www.erlang.org/.
+##
+## Software distributed under the License is distributed on an "AS IS"
+## basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See
+## the License for the specific language governing rights and limitations
+## under the License.
+##
+## %CopyrightEnd%
+##
+## File: erl-xcomp.conf.template
+## Author:
+##
+## -----------------------------------------------------------------------------
+## When cross compiling Erlang/OTP using `otp_build', copy this file and set
+## the variables needed below. Then pass the path to the copy of this file as
+## an argument to `otp_build' in the configure stage:
+##   `otp_build configure --xcomp-conf=<FILE>'
+## -----------------------------------------------------------------------------
+
+## Note that you cannot define arbitrary variables in a cross compilation
+## configuration file. Only the ones listed below will be guaranteed to be
+## visible throughout the whole execution of all `configure' scripts. Other
+## variables needs to be defined as arguments to `configure' or exported in
+## the environment.
+
+## -- Variables for `otp_build' Only -------------------------------------------
+
+## Variables in this section are only used, when configuring Erlang/OTP for
+## cross compilation using `$ERL_TOP/otp_build configure'.
+
+## *NOTE*! These variables currently have *no* effect if you configure using
+## the `configure' script directly.
+
+# * `erl_xcomp_build' - The build system used. This value will be passed as
+#   `--build=$erl_xcomp_build' argument to the `configure' script. It does
+#   not have to be a full `CPU-VENDOR-OS' triplet, but can be. The full
+#   `CPU-VENDOR-OS' triplet will be created by
+#   `$ERL_TOP/erts/autoconf/config.sub $erl_xcomp_build'. If set to `guess',
+#   the build system will be guessed using
+#   `$ERL_TOP/erts/autoconf/config.guess'.
+erl_xcomp_build=guess
+
+# * `erl_xcomp_host' - Cross host/target system to build for. This value will
+#   be passed as `--host=$erl_xcomp_host' argument to the `configure' script.
+#   It does not have to be a full `CPU-VENDOR-OS' triplet, but can be. The
+#   full `CPU-VENDOR-OS' triplet will be created by
+#   `$ERL_TOP/erts/autoconf/config.sub $erl_xcomp_host'.
+erl_xcomp_host=arm-linux-androideabi
+
+# * `erl_xcomp_configure_flags' - Extra configure flags to pass to the
+#   `configure' script.
+erl_xcomp_configure_flags="--disable-hipe --without-termcap"
+
+
+## -- Cross Compiler and Other Tools -------------------------------------------
+
+##
+##
+NDK_SYSROOT=$NDK_ROOT/platforms/$NDK_PLAT/arch-arm
+
+## If the cross compilation tools are prefixed by `<HOST>-' you probably do
+## not need to set these variables (where `<HOST>' is what has been passed as
+## `--host=<HOST>' argument to `configure').
+
+## All variables in this section can also be used when native compiling.
+
+# * `CC' - C compiler.
+CC="arm-linux-androideabi-gcc --sysroot=$NDK_SYSROOT"
+
+# * `CFLAGS' - C compiler flags.
+CFLAGS="-static -march=armv7-a -msoft-float -mthumb"
+
+# * `STATIC_CFLAGS' - Static C compiler flags.
+#STATIC_CFLAGS=
+
+# * `CFLAG_RUNTIME_LIBRARY_PATH' - This flag should set runtime library
+#   search path for the shared libraries. Note that this actually is a
+#   linker flag, but it needs to be passed via the compiler.
+#CFLAG_RUNTIME_LIBRARY_PATH=
+
+# * `CPP' - C pre-processor.
+CPP="arm-linux-androideabi-cpp --sysroot=$NDK_SYSROOT"
+
+# * `CPPFLAGS' - C pre-processor flags.
+CPPFLAGS="-static -march=armv7-a -msoft-float -mthumb"
+
+# * `CXX' - C++ compiler.
+CXX="arm-linux-androideabi-c++ --sysroot=$NDK_SYSROOT"
+
+# * `CXXFLAGS' - C++ compiler flags.
+CXXFLAGS="-static -march=armv7-a -msoft-float -mthumb"
+
+# * `LD' - Linker.
+#LD=
+
+# * `LDFLAGS' - Linker flags.
+LDFLAGS="-static -march=armv7-a -msoft-float -mthumb"
+
+# * `LIBS' - Libraries.
+#LIBS=
+
+## -- *D*ynamic *E*rlang *D*river Linking --
+
+## *NOTE*! Either set all or none of the `DED_LD*' variables.
+
+# * `DED_LD' - Linker for Dynamically loaded Erlang Drivers.
+#DED_LD=
+
+# * `DED_LDFLAGS' - Linker flags to use with `DED_LD'.
+#DED_LDFLAGS=
+
+# * `DED_LD_FLAG_RUNTIME_LIBRARY_PATH' - This flag should set runtime library
+#   search path for shared libraries when linking with `DED_LD'.
+#DED_LD_FLAG_RUNTIME_LIBRARY_PATH=
+
+## -- Large File Support --
+
+## *NOTE*! Either set all or none of the `LFS_*' variables.
+
+# * `LFS_CFLAGS' - Large file support C compiler flags.
+#LFS_CFLAGS=
+
+# * `LFS_LDFLAGS' - Large file support linker flags.
+#LFS_LDFLAGS=
+
+# * `LFS_LIBS' - Large file support libraries.
+#LFS_LIBS=
+
+## -- Other Tools --
+
+# * `RANLIB' - `ranlib' archive index tool.
+#RANLIB=
+
+# * `AR' - `ar' archiving tool.
+#AR=
+
+# * `GETCONF' - `getconf' system configuration inspection tool. `getconf' is
+#   currently used for finding out large file support flags to use, and
+#   on Linux systems for finding out if we have an NPTL thread library or
+#   not.
+#GETCONF=
+
+## -- Cross System Root Locations ----------------------------------------------
+
+# * `erl_xcomp_sysroot' - The absolute path to the system root of the cross
+#   compilation environment. Currently, the `crypto', `odbc', `ssh' and
+#   `ssl' applications need the system root. These applications will be
+#   skipped if the system root has not been set. The system root might be
+#   needed for other things too. If this is the case and the system root
+#   has not been set, `configure' will fail and request you to set it.
+erl_xcomp_sysroot="$NDK_SYSROOT"
+
+
+# * `erl_xcomp_isysroot' - The absolute path to the system root for includes
+#   of the cross compilation environment. If not set, this value defaults
+#   to `$erl_xcomp_sysroot', i.e., only set this value if the include system
+#   root path is not the same as the system root path.
+#erl_xcomp_isysroot=
+
+## -- Optional Feature, and Bug Tests ------------------------------------------
+
+## These tests cannot (always) be done automatically when cross compiling. You
+## usually do not need to set these variables. Only set these if you really
+## know what you are doing.
+
+## Note that some of these values will override results of tests performed
+## by `configure', and some will not be used until `configure' is sure that
+## it cannot figure the result out.
+
+## The `configure' script will issue a warning when a default value is used.
+## When a variable has been set, no warning will be issued.
+
+# * `erl_xcomp_after_morecore_hook' - `yes|no'. Defaults to `no'. If `yes',
+#   the target system must have a working `__after_morecore_hook' that can be
+#   used for tracking used `malloc()' implementations core memory usage.
+#   This is currently only used by unsupported features.
+#erl_xcomp_after_morecore_hook=
+
+# * `erl_xcomp_bigendian' - `yes|no'. No default. If `yes', the target system
+#   must be big endian. If `no', little endian. This can often be
+#   automatically detected, but not always. If not automatically detected,
+#   `configure' will fail unless this variable is set. Since no default
+#   value is used, `configure' will try to figure this out automatically.
+#erl_xcomp_bigendian=
+
+# * `erl_xcomp_clock_gettime_cpu_time' - `yes|no'. Defaults to `no'. If `yes',
+#   the target system must have a working `clock_gettime()' implementation
+#   that can be used for retrieving process CPU time.
+#erl_xcomp_clock_gettime_cpu_time=
+
+# * `erl_xcomp_getaddrinfo' - `yes|no'. Defaults to `no'. If `yes', the target
+#   system must have a working `getaddrinfo()' implementation that can
+#   handle both IPv4 and IPv6.
+#erl_xcomp_getaddrinfo=
+
+# * `erl_xcomp_gethrvtime_procfs_ioctl' - `yes|no'. Defaults to `no'. If `yes',
+#   the target system must have a working `gethrvtime()' implementation and
+#   is used with procfs `ioctl()'.
+#erl_xcomp_gethrvtime_procfs_ioctl=
+
+# * `erl_xcomp_dlsym_brk_wrappers' - `yes|no'. Defaults to `no'. If `yes', the
+#   target system must have a working `dlsym(RTLD_NEXT, <S>)' implementation
+#   that can be used on `brk' and `sbrk' symbols used by the `malloc()'
+#   implementation in use, and by this track the `malloc()' implementations
+#   core memory usage. This is currently only used by unsupported features.
+#erl_xcomp_dlsym_brk_wrappers=
+
+# * `erl_xcomp_kqueue' - `yes|no'. Defaults to `no'. If `yes', the target
+#   system must have a working `kqueue()' implementation that returns a file
+#   descriptor which can be used by `poll()' and/or `select()'. If `no' and
+#   the target system has not got `epoll()' or `/dev/poll', the kernel-poll
+#   feature will be disabled.
+#erl_xcomp_kqueue=
+
+# * `erl_xcomp_linux_clock_gettime_correction' - `yes|no'. Defaults to `yes' on
+#   Linux; otherwise, `no'. If `yes', `clock_gettime(CLOCK_MONOTONIC, _)' on
+#   the target system must work. This variable is recommended to be set to
+#   `no' on Linux systems with kernel versions less than 2.6.
+#erl_xcomp_linux_clock_gettime_correction=
+
+# * `erl_xcomp_linux_nptl' - `yes|no'. Defaults to `yes' on Linux; otherwise,
+#   `no'. If `yes', the target system must have NPTL (Native POSIX Thread
+#   Library). Older Linux systems have LinuxThreads instead of NPTL (Linux
+#   kernel versions typically less than 2.6).
+#erl_xcomp_linux_nptl=
+
+# * `erl_xcomp_linux_usable_sigaltstack' - `yes|no'. Defaults to `yes' on Linux;
+#   otherwise, `no'. If `yes', `sigaltstack()' must be usable on the target
+#   system. `sigaltstack()' on Linux kernel versions less than 2.4 are
+#   broken.
+#erl_xcomp_linux_usable_sigaltstack=
+
+# * `erl_xcomp_linux_usable_sigusrx' - `yes|no'. Defaults to `yes'. If `yes',
+#   the `SIGUSR1' and `SIGUSR2' signals must be usable by the ERTS. Old
+#   LinuxThreads thread libraries (Linux kernel versions typically less than
+#   2.2) used these signals and made them unusable by the ERTS.
+#erl_xcomp_linux_usable_sigusrx=
+
+# * `erl_xcomp_poll' - `yes|no'. Defaults to `no' on Darwin/MacOSX; otherwise,
+#   `yes'. If `yes', the target system must have a working `poll()'
+#   implementation that also can handle devices. If `no', `select()' will be
+#   used instead of `poll()'.
+#erl_xcomp_poll=
+
+# * `erl_xcomp_putenv_copy' - `yes|no'. Defaults to `no'. If `yes', the target
+#   system must have a `putenv()' implementation that stores a copy of the
+#   key/value pair.
+#erl_xcomp_putenv_copy=
+
+# * `erl_xcomp_reliable_fpe' - `yes|no'. Defaults to `no'. If `yes', the target
+#   system must have reliable floating point exceptions.
+#erl_xcomp_reliable_fpe=
+
+## -----------------------------------------------------------------------------