RFR: 8284437: Building from different users/workspace is not always deterministic [v2]

[Magnus Ihse Bursie]

On Thu, 7 Apr 2022 20:15:12 GMT, Erik Joelsson <erikj at openjdk.org> wrote:

>> @magicus 
>> So I did think about this, and the alternative I think would be to hard code a list of which object files are the output from assembly files, of which there is about a dozen. Unless we could capture somehow the list of assembled files as we go ...?
>> As @erikj79 points out this is just for the "linking". As the problem is the assembly file objects don't have the equivalent of debug prefix mapping, and so when stripped the full file path of the object file ends up in the debuginfo file, and results in the libjvm.so non-determinism due to different debug CRC.
>
> It would certainly be possible to identify the objects created from assembly source files based on file extensions, but it wouldn't help. The command line would still be dependent on the current working directory (correctly guessed!) if just one of the argument files is relative.
> 
> The property Magnus is trying to preserve is to be able to copy a command line from the build log and run it in whichever directory you happen to be in, without having to figure out what the CWD was for that particular command. We worked hard to try to figure out ways of preserving that as much as possible, but as you say, if we want true reproducibility, then we have to give it up for link command lines where assembly source files are included.
> 
> Now I realize that you aren't even checking if the link unit contains any objects from assembly files. I think we should be able to deduce that by filtering on the extension in the source file list. That would miss assembly input in EXTRA_OBJS, so perhaps we need an explicit parameter to SetupNativeCompilation for cases where this would happen. I think it applies to gtest, where we add all the object files from libjvm.

One way would be to check if we have either assembly source files, or anything in EXTRA_OBJ, and if so, do the relative linking. That would at least bring down collateral damage significantly, since the majority of libs have neither.

It will still hurt the most important libs (like hotspot) but unless we can't find a way to get this working in some other way, it seems we'll have to accept that.

@andrew-m-leonard Do you know if there is any bug on gcc tracking their inability to set debug prefix mapping for assembly files?

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PR: https://git.openjdk.java.net/jdk/pull/8124