[Buildroot] Build reproducibility
Thomas Petazzoni
thomas.petazzoni at free-electrons.com
Tue Sep 3 07:16:12 UTC 2013
Dear Peter Korsgaard,
On Tue, 03 Sep 2013 08:26:07 +0200, Peter Korsgaard wrote:
> Arnout> Note that doing more randomized build order in the autobuilder also
> Arnout> will not capture the latter scenario. You would have to compare the
> Arnout> build result - but binary differences are likely because of changing
> Arnout> timestamps or changing optimizations depending on memory randomness.
>
> Exactly. I don't have any good ideas about how to detect this (besides
> building all packages in clean staging dirs, E.G. only populated with
> its explicit dependencies like afaik OE lite can do, but that would
> require quite some work), anyone?
Doing a per-package sysroot that is generated for each package before
it gets built, with only the explicitly listed dependencies, is indeed
the only way to ensure that a package is not seeing/using something
that isn't declared as a dependency.
This would certainly be nice to have (as it also helps top-level
parallel build, as was discussed with Fabio Porcedda some time ago),
but:
1) I'm worried about the additional complexity inside Buildroot.
2) I'm worried about the additional build time required to generate a
per-package sysroot for each package. When building large stacks
like X.org that has many small packages, but each have a lot of
dependencies, the cost of creating a sysroot before building each
package could be huge.
3) We still need to provide the user a global sysroot with all
libraries installed, so that he can use the toolchain generated by
Buildroot to build his own libraries/applications. This would mean
we would need to have two sysroots: the global sysroot, that gets
incrementally populated with what all packages are installing, but
that isn't used for building packages inside Buildroot, and a
separate temporary sysroot, used when building the current package.
Since the compiler would default to the 'global sysroot', we would
have to pass --sysroot $(TMPSYSROOT) all the time, or have a
separate wrapper, or something. Not impossible, but see (1).
Best regards,
Thomas
--
Thomas Petazzoni, Free Electrons
Kernel, drivers, real-time and embedded Linux
development, consulting, training and support.
http://free-electrons.com
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