[pkg-GD-devel] Bug#867003: Bug#867003: FTBFS of libgd2 due to test failures

[Ondřej Surý]

Hi,

I think this is reasonable, but I would really appreciate patches for
autopkgtest.

Cheers,
Ondrej

On Mon, 25 Sep 2017 at 04:51 Jiri Palecek <jpalecek at web.de> wrote:

> Hello,
>
> I was looking at the recent FTBFS of libgd2, which prevented security
> fixes to reach debian archive for more than a week. The FTBFS were
> restricted to several architectures.
>
> By the look of it, it seems that the errors are simple arithmetical
> inaccuracies, when the tests expect pixel-exact results. I was
> specifically concerned about gdimagerotate/bug00067 test on i386, and
> the result of the rotate operation, while not comparing equal to the
> expected image, seemed the same to the naked eye.
>
> Slight differences of the computations on different architectures are to
> be expected, eg. if those architectures use different floating point
> formats, although it shouldn't matter that much in the test I mentioned
> (by rough estimate it should need a precision of about 1/2^18 -- 1/2^20,
> while IEE754 float is more precise than that). However, I was surprised
> that when I tested it with optimizations turned off, there were failures
> in the test suite too, but _different_ failures. This should mean
> there's something dodgy going on either in gcc or in the code.
>
> Anyway, I guess libgd2's aim isn't to provide pixel perfect image
> manipulations, but rather accessible image functions for eg. web servers
> in PHP. In that case, the testsuite doesn't really reflect the
> requirements it should fulfill, and it should focus more on security
> than accuracy.
>
> I would propose to ditch the testsuite completely from the building
> process of the package, since in its present state, it is inherently
> unreliable and would cause FTBFS. Instead, an autopkgtest testsuite
> could be made (with the running the same tests), which could be
> automatically ran using ci.debian.org. Such a testsuite could probably
> even be rigged to run under valgrind, which could catch some memory
> errors. At the same time, the testsuite could be made more lenient (or
> the library code more accurate), but that would require substantially
> more work and I don't know whether it would be desirable.
>
> Please let me know what you think.
>
> Regards
>
>      Jiri Palecek
>
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-- 
Ondřej Surý <ondrej at sury.org>
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