Reproducible Builds on Windows

[Jared Parsons]

The `--pathmap` option just serves to normalize file paths that are emitted
to the EXE / DLL or PDB by the C# compiler. There are a number of cases
where file paths are emitted like the PDB document table, [CallerFileInfo]
parameters, etc ... Using `--pathmap` allows these paths to be normalized
when building in different directories. If you're using the .NET SDK in
many cases you can just pass -p:DeterministicSourcePaths and this will be
done for you (that option should really have been called
ReproducibleSourcePaths).

The original question was more about MSVC though, believe they have a
similar option but unsure what the name is.

On Tue, Dec 3, 2024 at 3:05 AM Andrew Leonard <anleonar at redhat.com> wrote:

> For reproducible Windows builds of OpenJDK, we found the build PATH "hash"
> was an issue,
> i'm not totally sure if all those deterministic options can avoid it. We
> work around the issue
> by always using "relative" build paths for compilation.
> Have you tried also using the --pathmap: option to map source paths
> generated by the compiler?
> Not sure but it may make the "hashes" deterministic maybe...
> ref:
> https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/compiler-options/advanced
>
>
>
> On Mon, Dec 2, 2024 at 11:25 AM Chris Lamb <chris at reproducible-builds.org>
> wrote:
>
>> Danilo wrote:
>>
>> > https://try.diffoscope.org/hxsyehbrkftf.html (link valid for 30 days).
>> > There are no paths embedded in the binary. To me, this looks like some
>> > kind of optimization, but I don't know where it's coming from.
>>
>> I've come across more than one file format that _hashes_ the build
>> path and then uses that value as a debug/interface/build identifier.
>> Crucially, as the build path is hashed, it does not appear as a
>> literal string in the binary, so not seeing the build path in
>> diffoscope is not conclusive.
>>
>> Whilst I've seen this used as part of the Link-Time Optimisation
>> puzzle, the switch to disable stuff like that might be in the linker
>> or debug area of your compiler docs — not the optimisation part.
>>
>> That would be my guess anyway... Am throwing it over the wall given
>> you seem to be working on this as we type. :)  No doubt someone much
>> more informed about this file format will chime in and correct me.
>>
>>
>> Best wishes,
>>
>> --
>>       o
>>     ⬋   ⬊      Chris Lamb
>>    o     o     reproducible-builds.org 💠
>>     ⬊   ⬋
>>       o
>>
>>

-- 
Jared Parsons
http://blog.paranoidcoding.com/
http://twitter.com/jaredpar
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