The general rule for building JDK release N is that JDK N-1 should be used as the boot JDK. A check should be added to "configure" that stops with an error if it detects an improper JDK being used as the boot JDK.

See JDK-8016780 and this email thread for further discussion:

http://mail.openjdk.java.net/pipermail/build-dev/2013-June/009318.html

Unfortunately it is entirely possible for configure to pick up a JDK 8 instance as the boot JDK for building JDK 8, either because it was specified by the developer on the command line, or because it happened to occur in the PATH at the time configure was run. This is a mistake, as it might let JDK 8 dependencies creep into parts of the code that are built by JDK 7 (that is, using the JDK 7 class libraries). A configuration with the wrong boot JDK allowed JDK-8015978 to cause a build failure, which subsequently was fixed by JDK-8016701.

It should probably be possible to override configure's boot JDK version check by providing some option explicitly.

Of course, the build system would have to override or otherwise deal with the JDK N-1 requirement when doing a boot cycle build.