JDK 9 RFR of JDK-8072480: javac should support compilation for a specific platform version

Jan Lahoda jan.lahoda at oracle.com
Fri May 22 13:22:39 UTC 2015

On 22.5.2015 14:52, Maurizio Cimadamore wrote:
> Excellent work.
> I think the comment in CreateSymbols could be made clearer w.r.t. Probe
> - i.e. that Probe should be ran on top of the JDK N - i.e.
> <JDK-8>/bin/java Probe --> classes-8
> <JDK-7>/bin/java Probe --> classes-7
> <JDK-6>/bin/java Probe --> classes-7
> etc.

Sure, will do.

I'll also look at generating the make/data/symbols/symbols descriptions 
automatically, per our offline discussion.



> Maurizio
> On 22/05/15 13:38, Jan Lahoda wrote:
>> Hi,
>> I've uploaded a new iteration of the patch(es):
>> top-level repository:
>> http://cr.openjdk.java.net/~jlahoda/8072480/webrev.01/top-level/
>> langtools:
>> http://cr.openjdk.java.net/~jlahoda/8072480/webrev.01/langtools/
>> (besides full webrevs, there are also webrevs showing the differences
>> between .00 and .01 available - see the "Delta webrev" link under
>> "Author's comments")
>> Summary of changes:
>> -applied Eric's build changes
>> -moved CreateSymbols into make/src/classes/build/tools/symbolgenerator
>> -tried to improve the specification of base platforms in
>> CreateSymbols, per Maurizio's comment
>> -other cleanup in langtools per Maurizio's comments.
>> Thanks,
>>     Jan
>> On 21.5.2015 12:31, Maurizio Cimadamore wrote:
>>> Hi Jan,
>>> great work - couple of comments below:
>>> * it seems like some of the routines in Arguments can be simplified
>>> using lambdas - especially lookupPlatformProvider and checkOptionAllowed
>>> * Why JDKPlatformProvider is not called JDKPlatformProvider*Factory* ?
>>> * JavacProcessingEnvironment.JoiningIterator seems to have commonalities
>>> with CompoundScopeIterator - any chance that we might refactor this a
>>> bit?
>>> * What's the rationale for giving an error if -platform is specified and
>>> a non-StandardFileManager is provided? Can't we simply swallow that,
>>> ignore the platform settings and issue a Lint 'options' warning?
>>> * Would it make sense for some of the classfile generation logic in
>>> CreateSymbols to be moved under the classfile API ?
>>> * I had hard time reconciling some of the comments in CreateSymbols with
>>> how the files were laid out. I think in the end, what you mean is that
>>> if you have platforms 7, 8, 9 - you should pick one baseline (i.e. 8)
>>> and then generate diffs for 9 and 7 against the 8 one. If that's the use
>>> case, I think the command line can be simplified a bit in order to
>>> explicitly state which of the platform is the baseline one, and the
>>> remaining parameters can be inferred from the tool (as the
>>> <base-platform-for-platform1,2 ... N> seem to be typically all identical
>>> but one which is set to <none> - the one for the baseline). Maybe the
>>> inference logic should be different (i.e. use 8 as a baseline for 7 and
>>> 7 as a baseline for 6) - but - whatever the logic, I think it should be
>>> chosen once and for all, and live implicitly in the tool? Or are there
>>> reasons as to why it might be handy to customize the baselines?
>>> Maurizio
>>> On 21/05/15 08:01, Jan Lahoda wrote:
>>>> Hi,
>>>> This is a patch adding a new option, -platform, to javac.
>>>> Patch for the top-level repository is here:
>>>> http://cr.openjdk.java.net/~jlahoda/8072480/webrev.00/top-level/
>>>> Patch for the langtools repository is here:
>>>> http://cr.openjdk.java.net/~jlahoda/8072480/webrev.00/langtools/
>>>> These changes also require additional langtools changes as their
>>>> prerequisite:
>>>> http://cr.openjdk.java.net/~jlahoda/8080675/webrev.00/
>>>> Overall, one can imagine '-platform N' to have the same effect as
>>>> '-source N -target N -bootclasspath <APIs-for-N>'. The possible values
>>>> for 'N' are pluggable in a limited way, though (see
>>>> langtools/src/jdk.compiler/share/classes/com/sun/tools/javac/platform/PlatformProvider.java).
>>>> Note that this patch only introduces N=7 and N=8, which correspond to
>>>> Open JDK 7 and 8 GA.
>>>> A tricky problem to solve is where to get the APIs for platform N. The
>>>> proposal is to include history data in the textual format inside the
>>>> OpenJDK repositories (the input data), process them at build time and
>>>> create a lib/ct.sym file holding the data in the JDK image. javac
>>>> running with the -platform option then compiles against the lib/ct.sym
>>>> file. The input history data are placed
>>>> <top-level-repository>/make/data/symbols (the sym.txt files). This
>>>> patches only includes data for OpenJDK 7 and 8, and only for public
>>>> APIs (more or less Java SE and JDK @Exported APIs).
>>>> The size of the history data is currently ~6MB in the JDK checkout and
>>>> ~650kB inside the .hg directory (the size could change significantly
>>>> if additional classes/elements, like non-public API classes, would
>>>> need to be included). The lib/ct.sym file is currently ~4.5MB.
>>>> The ct.sym file is a zip file containing signature files. The
>>>> signature files are similar to classfiles (so javac can read them as
>>>> classfiles), but are missing some attributes, most notably the Code
>>>> attribute. On the top-level, the ct.sym contains directories named
>>>> "7", "78" and "8". When compiling for version 'N', the bootclasspath
>>>> for that version is obtained by using directories which have 'N' in
>>>> their name.
>>>> The sigfiles for ct.sym are created by
>>>> <top-level-repository>/make/tools/symbolgenerator/CreateSymbols.java.
>>>> The same file can also be used to construct the sym.txt files. Concise
>>>> instructions are part of the CreateSymbols.java.
>>>> I am sending this as one review, as the changes together make one
>>>> feature, but the langtools and top-level changes are independent to a
>>>> great degree: the langtools changes add the "-platform" javac; and the
>>>> top-level changes add the history data and ability to build the ct.sym
>>>> file. If desired, these could be pushed and/or reviewed independently.
>>>> Many thanks go to Jon Gibbons, Joe Darcy, Magnus Ihse Bursie, Alan
>>>> Bateman and others who have provided advices and help on the matter
>>>> before.
>>>> Any insights/comments are wholeheartedly welcome.
>>>> Thanks,
>>>>     Jan

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