Should we build jrt-fs.jar again with the "Build JDK" ?

[Magnus Ihse Bursie]

On 2023-09-20 09:38, Andrew Leonard wrote:

> Thanks Alan,
>
> So different gcc, glibc, Xcode,.. agree, they need to be the same for 
> identical bits.
> However, at the moment using the same toolchains, if you do a standard 
> product build,
> and then a bootcycle build, of the same source, jrt-fs.jar will differ.
> I'll do some investigation of the make files to see if a "Build JDK" 
> rebuild of jrt-fs.jar is
> feasible.

I would not in general assume that a normal build and a bootcycle build 
produce identical results. A bootcycle build will build the product 
using a newer version of the JDK (viz. the one you just build from the 
sources), and as such, changes to javac can result in different class 
file outputs, etc. That being said, for large time periods of the JDK 
source code, a normal build and a bootcycle build can certainly result 
in the same output, since no changes have been made in the product that 
affects how .class files are generated. But that is not guaranteed, nor 
is a difference between normal and bootcycle build a sign of trouble or 
a defect.

If jrt-fs.jar is consistently different between a bootcycle build and a 
normal build, that sounds a bit odd, though. Especially since it should 
be built with `--release 8` (or something like that) to ensure it is 
usable on older Java; and that output ought not to really change as the 
JDK develops.

(Also, questions about the build process is preferably handled on the 
build-dev list)

/Magnus


>
> Cheers
> Andrew
>
>
> On Tue, Sep 19, 2023 at 5:42 PM Alan Bateman <Alan.Bateman at oracle.com> 
> wrote:
>
>     On 18/09/2023 14:51, Andrew Leonard wrote:
>     > Thanks for the clarification Alan.
>     >
>     > To ensure the reproducibility of the whole JDK image regardless
>     of the
>     > specific bootjdk used, would it make sense once the "Build JDK" has
>     > been built, we re-build jrt-fs.jar again using the "Build JDK" ?
>     Thus
>     > jrt-fs.jar will be consistent with the rest of the image in
>     terms of
>     > what it is compiled with.
>     >
>
>     The boot JDK will be JDK N-1, or the newly built JDK in the case
>     of boot
>     cycle builds. It seems a bit of a stretch to have builds using
>     different
>     tool chains to produce identical bits but maybe you mean something
>     else.
>
>     In any case, for jrt-fs.jar the important thing is that they are
>     compiled to --release 8 (that might rev at some points) so that
>     IDEs/tools can open a target run-time image as a file system and
>     access
>     the classes/resources.
>
>     -Alan.
>
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