[Nix-dev] Deterministic(bit-perfect) Builds

[Vladimír Čunát]

On 06/25/2013 11:43 AM, phreedom at yandex.ru wrote:
>> Wouldn't it be more certain/universal to LD_PRELOAD or something to
>> achieve that the system time always looks the same to any build-time
>> tool? (e.g. UNIX time =0)
>
> This is a bit platform-specific and there may be other gotchas like getting the
> mtime using stat instead of querying system time. Other impurities in static
> libs are uid/gid of the file.

I would think that the file timestamps also originate from system time 
so we could kill more birds with one stone... but I don't have a clue 
whether/how such a sandbox can be done easily (in Linux; I assume our 
main target for purity is Linux, the others are impure for other reasons 
as well).

>>> Unstripped binaries: may be contaminated by "build-id". Can be avoided
>>> either by passing ld --build-id=none param or careful stripping. Needs
>>> testing. Luckily this is a very small subset of packages.
>>
>> I looked at "man ld" and I think we rather want --build-id=sha1 as it's
>> explicitly stated that the ID is uniquely determined by the output.
>
> I haven't checked for sure but vandenoever's tests seem to indicate that the
> default build id is in fact sha1 and it depends on the build dir :(

Ah, well, from [buildID docs] it doesn't seems so, but we can do with 
--build-id=none... paths are unique IDs already :-)

[buildID docs] 
https://fedoraproject.org/wiki/Releases/FeatureBuildId#Add_BuildID_Support


Vlada


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