Re: [dpdk-dev] [PATCH v6 00/11] Add ABI compatibility checks to the meson build

[Thomas Monjalon <thomas@monjalon.net>]

19/12/2019 22:58, David Marchand:
> On Fri, Dec 13, 2019 at 5:41 PM Kevin Laatz <kevin.laatz@intel.com> wrote:
> > The proposed solution works as follows:
> > 1. Generate the ABI dump of the baseline. This can be done with the new
> >    script added in this set. This step will only need to be done when the
> >    ABI version changes (so once a year) and can be added to master so it
> >    exists by default. This step can be skipped if the dump files for the
> >    baseline already exist.
> > 2. Build with meson. If there is an ABI incompatibility, the build will
> >    fail and print the incompatibility information.
[...]
> - I asked for the dump files, but I can see that it is impractical.
> 
> The dump files are huge. I did not expect that :-).
> The dump files are architecture specific and maintaining multi arch
> dumps would be even bigger than just what you sent for x86_64.
> (not even considering the changes in ABI if some configuration items
> have an impact...).

I agree that dump files are better managed outside of git.


> As you pointed out, people who don't have all dependencies won't
> create/update those dump files.
> Dealing with ABI updates (thinking of bumping the ABI version) is
> likely a maintainer job, but it will be a source of issues and we
> (maintainers) might miss some updates especially for drivers we can't
> build.
> 
> 
> - Why do we restrict the checks to meson?
> The make build framework is going to disappear ok, but we can't leave
> it untested.
> People still rely on it.
> 
> Checking the ABI is orthogonal to building DPDK.
> Dumping the ABI and checking it against objects can be done externally.

I agree we should not rely on meson for running the check.


> - For those reasons, I have been trying an alternate approach [1]: in
> Travis, generate a reference dump based on the first ancestor tag,
> then build the proposed patches.
> All contributions get picked up by Aaron robot and would have to pass
> through this check.
> 
> As an exercise, I tried to integrate Eelco patch [2], that moves
> symbols from EXPERIMENTAL to a stable ABI. The check passes fine.
> I also tried to bump the ABI major version. The check fails, as
> expected, but I prepared a way to bypass such failures for the
> releases where we will explicitely break ABI.
> 
> For maintainers that integrate patches or developers that get a CI
> failure and want to fix it, we would need to help them to:
> * generate dumps on a reference version, so I would tend to write some
> documentation since playing with the current sources would be too
> dangerous from my pov,
> * run the checks, like adding the check in the
> devtools/test-*-build.sh scripts that already exist, with a new
> configuration item to point at the dumps per target,

We can start with a documented process,
and write a separate script later if we feel it helps.


> Those last two points are still to be done.
> 
> WDYT?
> 
> 
> 1: https://github.com/david-marchand/dpdk/commit/f18de2ec157f3cc1e7b319cb19700e1b5e9cecde
> 2: https://patchwork.dpdk.org/patch/63970/


Thanks to both of you trying some approaches and making progress.