zero build slow

[Erik Joelsson]

Hello,

On 2017-11-22 08:30, Thomas Stüfe wrote:
> On Wed, Nov 22, 2017 at 4:40 PM, Andrew Haley <aph at redhat.com> wrote:
>
>> On 22/11/17 15:29, Thomas Stüfe wrote:
>>> when building zero on Linux x64, I notice that the build is extremely
>> slow,
>>> due to what I assume is jmod ran from the built image, which would only
>> run
>>> interpreted? Is my guess true, and if yes, is it possible to use a
>>> different jmod? I assume it is not possible to use jmod from the build
>> jdk?
>>
>> No, because the bootstrap JDK is version N-1.
>>
>>
> Ah, right.
>
>
>> Hmm, I wonder if you could cross-compile the JDK from x86 native -> x86
>> zero.
>>
> Does it have to be from the same build? If I build zero and normal product
> from the same head, could I not use the jmod from the product build for
> zero?
>
Yes you can indeed! There is a configure option:

   --with-build-jdk        path to JDK of same version as is being built[the
                           newly built JDK]

If set, this jdk is used instead of the newly built jdk for any tool 
that needs to run, like jmod and jlink. I realize the help text could be 
more elaborate in explaining this. This option is meant for your usecase 
as well as an option to speed up cross compilation builds. (When cross 
compiling, we otherwise have to build a minimal jdk for the host system 
to run jmod and jlink during the build.)

Note that for best performance, point this to the images/jdk directory 
of the release (non debug) build of the jdk for the native platform. 
Also note that it's only guaranteed to work if you use the exact same 
version as you are building zero from. If your build-jdk gets stale, 
weird things can start happening.

/Erik