8290466: Default to --with-source-date=current to avoid unmodified Hotspot recompilation

doc/building.html

@@ -898,13 +898,13 @@ <h2 id="reproducible-builds">Reproducible Builds</h2>
 <pre><code>export SOURCE_DATE_EPOCH=946684800
 bash configure --with-version-opt=adhoc
 make</code></pre>
-<p>Note that regardless if you specify a source date for <code>configure</code> or not, the JDK build system will set <code>SOURCE_DATE_EPOCH</code> for all build tools when building. If <code>--with-source-date</code> has the value <code>updated</code> (which is the default unless <code>SOURCE_DATE_EPOCH</code> is found by in the environment by <code>configure</code>), the source date value will be determined at build time.</p>
+<p>Note that regardless if you specify a source date for <code>configure</code> or not, the JDK build system will set <code>SOURCE_DATE_EPOCH</code> for all build tools when building. If <code>--with-source-date</code> has the value <code>current</code> (which is the default unless <code>SOURCE_DATE_EPOCH</code> is found by in the environment by <code>configure</code>), the source date value will be determined at configure time.</p>
 <p>There are several aspects of reproducible builds that can be individually adjusted by <code>configure</code> arguments. If any of these are given, they will override the value derived from <code>SOURCE_DATE_EPOCH</code>. These arguments are:</p>
 <ul>
 <li><p><code>--with-source-date</code></p>
 <p>This option controls how the JDK build sets <code>SOURCE_DATE_EPOCH</code> when building. It can be set to a value describing a date, either an epoch based timestamp as an integer, or a valid ISO-8601 date.</p>
 <p>It can also be set to one of the special values <code>current</code>, <code>updated</code> or <code>version</code>. <code>current</code> means that the time of running <code>configure</code> will be used. <code>version</code> will use the nominal release date for the current JDK version. <code>updated</code>, which means that <code>SOURCE_DATE_EPOCH</code> will be set to the current time each time you are running <code>make</code>. All choices, except for <code>updated</code>, will set a fixed value for the source date timestamp.</p>
-<p>When <code>SOURCE_DATE_EPOCH</code> is set, the default value for <code>--with-source-date</code> will be the value given by <code>SOURCE_DATE_EPOCH</code>. Otherwise, the default value is <code>updated</code>.</p></li>
+<p>When <code>SOURCE_DATE_EPOCH</code> is set, the default value for <code>--with-source-date</code> will be the value given by <code>SOURCE_DATE_EPOCH</code>. Otherwise, the default value is <code>current</code>.</p></li>
 <li><p><code>--with-hotspot-build-time</code></p>
 <p>This option controls the build time string that will be included in the hotspot library (<code>libjvm.so</code> or <code>jvm.dll</code>). When the source date is fixed (e.g. by setting <code>SOURCE_DATE_EPOCH</code>), the default value for <code>--with-hotspot-build-time</code> will be an ISO 8601 representation of that time stamp. Otherwise the default value will be the current time when building hotspot.</p></li>
 <li><p><code>--with-copyright-year</code></p>

doc/building.md

@@ -1559,9 +1559,9 @@ make
 
 Note that regardless if you specify a source date for `configure` or not, the
 JDK build system will set `SOURCE_DATE_EPOCH` for all build tools when building.
-If `--with-source-date` has the value `updated` (which is the default unless
+If `--with-source-date` has the value `current` (which is the default unless
 `SOURCE_DATE_EPOCH` is found by in the environment by `configure`), the source
-date value will be determined at build time.
+date value will be determined at configure time.
 
 There are several aspects of reproducible builds that can be individually
 adjusted by `configure` arguments. If any of these are given, they will override
@@ -1582,7 +1582,7 @@ the value derived from `SOURCE_DATE_EPOCH`. These arguments are:
 
     When `SOURCE_DATE_EPOCH` is set, the default value for `--with-source-date`
     will be the value given by `SOURCE_DATE_EPOCH`. Otherwise, the default value
-    is `updated`.
+    is `current`.
 
  * `--with-hotspot-build-time`
 

make/autoconf/jdk-options.m4

@@ -648,7 +648,7 @@ AC_DEFUN([JDKOPT_ALLOW_ABSOLUTE_PATHS_IN_OUTPUT],
 AC_DEFUN_ONCE([JDKOPT_SETUP_REPRODUCIBLE_BUILD],
 [
   AC_ARG_WITH([source-date], [AS_HELP_STRING([--with-source-date],
-      [how to set SOURCE_DATE_EPOCH ('updated', 'current', 'version' a timestamp or an ISO-8601 date) @<:@updated/value of SOURCE_DATE_EPOCH@:>@])],
+      [how to set SOURCE_DATE_EPOCH ('updated', 'current', 'version' a timestamp or an ISO-8601 date) @<:@current/value of SOURCE_DATE_EPOCH@:>@])],
       [with_source_date_present=true], [with_source_date_present=false])
 
   if test "x$SOURCE_DATE_EPOCH" != x && test "x$with_source_date" != x; then
@@ -665,9 +665,9 @@ AC_DEFUN_ONCE([JDKOPT_SETUP_REPRODUCIBLE_BUILD],
       with_source_date_present=true
       AC_MSG_RESULT([$SOURCE_DATE, from SOURCE_DATE_EPOCH])
     else
-      # Tell the makefiles to update at each build
-      SOURCE_DATE=updated
-      AC_MSG_RESULT([determined at build time (default)])
+      # Tell makefiles to take the time from configure
+      SOURCE_DATE=$($DATE +"%s")
+      AC_MSG_RESULT([$SOURCE_DATE, from 'current' (default)])
     fi
   elif test "x$with_source_date" = xupdated; then
     SOURCE_DATE=updated