Make Erlang installation file system location independent

Previously shell scripts (e.g., `erl` and `start`) and the RELEASES file
for an Erlang installation depended on hard coded absolute path to the
installation's root directory. This made it cumbersome to move a
release to a different directory and can be problematic for platforms
such as Android (erlang#2879) where the
installation directory is unknown at compile time. This is fixed by:

* Changing the shell scripts so that they can dynamically find the
  `ROOTDIR`. The dynamically found `ROOTDIR` is selected if it differs
  from the hard-coded `ROOTDIR` and seems to point to a valid Erlang
  installation. The `dyn_erl` program has been changed so that it can
  return its absolute canonicalized path when given the `--realpath`
  argument (dyn_erl gets its absolute canonicalized path from the
  `realpath` POSIX function). The `dyn_erl`'s `--realpath`
  functionality is used by the scripts to get the root dir dynamically.

* Changing the `release_handler` module that reads and writes to the
  `RELEASES` file so that it prepends `code:root_dir()` whenever it
  encounters relative paths. This is necessary since the current
  working directory can be changed so it is something different than
  `code:root_dir()`.

Makefile.in

@@ -577,10 +577,12 @@ else
 bootstrap_setup: check_recreate_primary_bootstrap bootstrap_setup_target $(BOOTSTRAP_ROOT)/bootstrap/bin/erl $(BOOTSTRAP_ROOT)/bootstrap/bin/erlc $(BOOTSTRAP_ROOT)/bootstrap/bin/escript $(BOOTSTRAP_ROOT)/bootstrap/bin/yielding_c_fun
 
 $(BOOTSTRAP_ROOT)/bootstrap/bin/erl: $(ERL_TOP)/erts/etc/unix/erl.src.src $(BOOTSTRAP_ROOT)/bootstrap/target
-	@rm -f $(BOOTSTRAP_ROOT)/bootstrap/bin/erl 
+	@rm -f $(BOOTSTRAP_ROOT)/bootstrap/bin/erl
 	@sed	-e "s;%FINAL_ROOTDIR%;$(BOOTSTRAP_ROOT)/bootstrap;"   \
 		-e "s;\$$ROOTDIR/erts-.*/bin;$(ERL_TOP)/bin/$(TARGET);"    \
 		-e "s;EMU=.*;EMU=beam$(TYPEMARKER);" \
+		-e "s;%DYN_ERL_PATH%;../../bin/$(TARGET)/dyn_erl;" \
+		-e "s;%DYN_ROOTDIR_BASE_EXT%;/bootstrap;"	\
 	        $(ERL_TOP)/erts/etc/unix/erl.src.src > \
 			$(BOOTSTRAP_ROOT)/bootstrap/bin/erl
 	@chmod 755 $(BOOTSTRAP_ROOT)/bootstrap/bin/erl

erts/Makefile

@@ -90,10 +90,13 @@ local_setup:
 	sed	-e "s;%FINAL_ROOTDIR%;$(ERL_TOP);"   \
 		-e "s;erts-.*/bin;bin/$(TARGET);"    \
 		-e "s;EMU=.*;EMU=beam$(TYPEMARKER);" \
+		-e "s;%DYN_ERL_PATH%;$(TARGET)/dyn_erl;" \
+		-e "s;%DYN_ROOTDIR_BASE_EXT%;;" \
 	        $(ERL_TOP)/erts/etc/unix/erl.src.src > $(ERL_TOP)/bin/erl; \
 	sed	-e "s;%SRC_ROOTDIR%;$(ERL_TOP);"   \
 		-e "s;%TARGET%;$(TARGET);"    \
 		-e "s;%VSN%;$(VSN);"    \
+		-e "s;%DYN_ERL_PATH%;$(TARGET)/dyn_erl;" \
 	        $(ERL_TOP)/erts/etc/unix/cerl.src > $(ERL_TOP)/bin/cerl; \
 		cp $(ERL_TOP)/bin/$(TARGET)/erl_call $(ERL_TOP)/bin/erl_call; \
 		cp $(ERL_TOP)/bin/$(TARGET)/dialyzer $(ERL_TOP)/bin/dialyzer; \

erts/etc/common/Makefile.in

@@ -517,6 +517,8 @@ erl.src: $(UXETC)/erl.src.src ../../vsn.mk $(TARGET)/Makefile
 	$(vsn_verbose)sed -e 's;%EMULATOR%;$(EMULATOR);' \
             -e 's;%EMULATOR_NUMBER%;$(EMULATOR_NUMBER);' \
             -e 's;%VSN%;$(VSN);' \
+            -e 's;%DYN_ERL_PATH%;../erts-$(VSN)/bin/dyn_erl;' \
+            -e 's;%DYN_ROOTDIR_BASE_EXT%;;' \
                   $(UXETC)/erl.src.src > erl.src
 
 # ----------------------------------------------------

erts/etc/unix/Install.src

@@ -81,7 +81,9 @@ chmod 755 erl
 # Create start file for embedded system use,
 #
 (cd "$ERL_ROOT/erts-%I_VSN%/bin";
-  sed -e "s;%FINAL_ROOTDIR%;$TARGET_ERL_ROOT;" start.src > start;
+ sed -e "s;%FINAL_ROOTDIR%;$TARGET_ERL_ROOT;" \
+     -e "s;%VSN%;%I_VSN%;" \
+     start.src > start;
   chmod 755 start)
 
 cd "$ERL_ROOT/bin"
@@ -113,7 +115,7 @@ sed -e "s;%EMU%;%EMULATOR%%EMULATOR_NUMBER%;" "$ERL_ROOT/erts-%I_VSN%/bin/start_
 chmod 755 start_erl
 
 echo %I_VSN% %I_SYSTEM_VSN% > "$ERL_ROOT/releases/start_erl.data"
-sed -e "s;%ERL_ROOT%;$TARGET_ERL_ROOT;" "$ERL_ROOT/releases/RELEASES.src" > "$ERL_ROOT/releases/RELEASES"
+sed -e "s;%ERL_ROOT%/;;" "$ERL_ROOT/releases/RELEASES.src" > "$ERL_ROOT/releases/RELEASES"
 
 if [ "$start_option" = "query" ]
 then

erts/etc/unix/cerl.src

@@ -81,8 +81,27 @@ run_asan=no
 run_rr=no
 skip_erlexec=no
 
+prog="$0"
+progdir="`dirname ${prog}`"
+dyn_erl_path="${progdir}/%DYN_ERL_PATH%"
+if [ -f "$dyn_erl_path" ]
+then
+    dyn_rootdir=`${dyn_erl_path} --realpath`
+    dyn_rootdir=`dirname ${dyn_rootdir}`
+    dyn_rootdir=`dirname ${dyn_rootdir}`
+else
+    dyn_rootdir=""
+fi
+
 # Default rootdir
 ROOTDIR=%SRC_ROOTDIR%
+
+if [ "$dyn_rootdir" != "$ROOTDIR" ] && [ "$dyn_rootdir" != "" ]
+then
+    # It is likely that the files have been copied or moved
+    ROOTDIR="$dyn_rootdir"
+fi
+
 BINDIR="$ROOTDIR/bin/`$ROOTDIR/make/autoconf/config.guess`"
 TARGET=%TARGET%
 #BINDIR="$ROOTDIR/bin/%TARGET%"

erts/etc/unix/dyn_erl.c

@@ -362,6 +362,15 @@ main(int argc, char **argv)
     char progname[PATH_MAX]; /* Name of this program. */
     char erlexec[PATH_MAX];  /* Path to erlexec */
 
+    if (argc == 2 && strcmp(argv[1], "--realpath") == 0) {
+        abspath = find_prog(argv[0]);
+        /* Remove program name from output */
+        for (p = abspath+strlen(abspath)-1;p >= abspath && *p != '/'; --p)
+            ;
+        *p = '\0';
+        printf("%s", abspath);
+        return 0;
+    }
     /* Determine progname */
     abspath = find_prog(argv[0]);
     strcpy(progname, abspath);

erts/etc/unix/erl.src.src

@@ -18,9 +18,32 @@
 #
 # %CopyrightEnd%
 #
+prog="$0"
+progdir="`dirname ${prog}`"
+dyn_erl_path="${progdir}/%DYN_ERL_PATH%"
+if [ ! -f "$dyn_erl_path" ]
+then
+    dyn_erl_path="${progdir}/dyn_erl"
+fi
+
+if [ -f "$dyn_erl_path" ]
+then
+    dyn_rootdir=`${dyn_erl_path} --realpath`
+    dyn_rootdir=`dirname ${dyn_rootdir}`
+    dyn_rootdir=`dirname ${dyn_rootdir}`
+    dyn_rootdir="${dyn_rootdir}%DYN_ROOTDIR_BASE_EXT%"
+else
+    dyn_rootdir=""
+fi
+
 if [ -z "$ERL_ROOTDIR" ]
 then
     ROOTDIR="%FINAL_ROOTDIR%"
+    if [ "$dyn_rootdir" != "$ROOTDIR" ] && [ "$dyn_rootdir" != "" ]
+    then
+        # It is likely that the files have been copied or moved
+        ROOTDIR="$dyn_rootdir"
+    fi
 else
     ROOTDIR="$ERL_ROOTDIR"
 fi

erts/etc/unix/start.src

@@ -25,9 +25,31 @@
 #
 # Usage: start [Data]
 #
+prog="$0"
+progdir="`dirname ${prog}`"
+dyn_erl_path="${progdir}/../erts-%VSN%/bin/dyn_erl"
+if [ ! -f "$dyn_erl_path" ]
+then
+    dyn_erl_path="${progdir}/dyn_erl"
+fi
+
+if [ -f "$dyn_erl_path" ]
+then
+    dyn_rootdir=`${dyn_erl_path} --realpath`
+    dyn_rootdir=`dirname ${dyn_rootdir}`
+    dyn_rootdir=`dirname ${dyn_rootdir}`
+else
+    dyn_rootdir=""
+fi
+
 if [ -z "$ERL_ROOTDIR" ]
 then
     ROOTDIR="%FINAL_ROOTDIR%"
+    if [ "$dyn_rootdir" != "$ROOTDIR" ] && [ "$dyn_rootdir" != "" ]
+    then
+        # It is likely that the files have been copied or moved
+        ROOTDIR="$dyn_rootdir"
+    fi
 else
     ROOTDIR="$ERL_ROOTDIR"
 fi

lib/sasl/doc/src/release_handler.xml

@@ -215,12 +215,19 @@
         <p>Creates an initial <c>RELEASES</c> file to be used by the
           release handler. This file must exist to install new
           releases.</p>
-        <p><c>Root</c> is the root of the installation (<c>$ROOT</c>) as
-          described earlier. <c>RelDir</c> is the directory where
-          the <c>RELEASES</c> file is to be created (normally
-          <c>$ROOT/releases</c>). <c>RelFile</c> is the name
-          of the <c>.rel</c> file that describes the initial release,
-          including the extension <c>.rel</c>.</p>
+        <p><c>Root</c> is the root of the installation (<c>$ROOT</c>)
+        as described earlier. <c>RelDir</c> is the directory where the
+        <c>RELEASES</c> file is to be created (normally
+        <c>$ROOT/releases</c>). <c>RelFile</c> is the name of the
+        <c>.rel</c> file that describes the initial release, including
+        the extension <c>.rel</c>. If <c>Root</c> is an empty string,
+        the <c>RELEASES</c> file will be location independent (i.e, it
+        will not contain absolute paths unless there are absolute
+        paths in <c>AppDirs</c>). A <c>RELEASES</c> file should be
+        made location independent if the installation's <c>$ROOT</c>
+        is unknown. The <c>release_handler</c> module will interpret
+        relative paths in a running system's <c>RELEASES</c> file as
+        being relative to <c>$ROOT</c>.</p>
         <p><c>AppDirs</c> can be used to specify from where the modules
           for the specified applications are to be loaded. <c>App</c> is
           the name of an application, <c>Vsn</c> is the version, and