RFR: JDK-8241271 Make hotspot build reproducible

[Magnus Ihse Bursie]

On 2020-03-19 19:01, Erik Joelsson wrote:
> On 2020-03-19 10:20, Magnus Ihse Bursie wrote:
>> Currently, it is not possible two make hotspot builds reproducible, 
>> since the current date and time is always inserted using the special 
>> macros __DATE__ and __TIME__. This patch makes it possible to 
>> override these values from the build system, paving the way for 
>> making re-builds of hotspot bit-by-bit identical.
>>
> I like the ability to achieve this.
>> On linux/gcc, we can now actually get bit-by-bit identical builds of 
>> libjvm.so (if not using precompiled headers), so I've updated the 
>> baseline-cmp profiles and compare script to reflect this.
>>
> I'm not sure this is a good idea though. It means I can't reasonably 
> compare to validate build changes that affect the precompiled header. 
> Similarly, the COMPARE_BUILD make variable argument will not work 
> unless you use both of these configure arguments.
>
> Since compare.sh is generated through configure, perhaps these 
> exceptions can be made conditional on if these configure arguments are 
> setup correctly for a reproducible libjvm.so?

Good thinking! I did not think of this possibility. And yes, I too did 
not like the current solution, but could think of no way around it. 
Here's an improved webrev.

WebRev: 
http://cr.openjdk.java.net/~ihse/JDK-8241271-make-hotspot-reproducible/webrev.02

Technically, you can make this fail by setting HOTSPOT_BUILD_TIME but to 
different values, but hey, there's no need to make this idiot-proof.

/Magnus
>
> /Erik
>
>> Bug: https://bugs.openjdk.java.net/browse/JDK-8241271
>> WebRev: 
>> http://cr.openjdk.java.net/~ihse/JDK-8241271-make-hotspot-reproducible/webrev.01
>>
>> /Magnus