[R-pkg-devel] Debugging Clang ASAN errors

[Iñaki Ucar]

On Fri, 3 Jul 2020 at 12:19, Martin R. Smith <martin.smith using durham.ac.uk> wrote:
>
> A package I recently had accepted to CRAN is throwing up a "memory not
> mapped" segfault on CRAN's post-acceptance fedora-clang ASAN test.  This
> error does not occur with debian-clang or gcc.
> (Check results:
> https://cran.r-project.org/web/checks/check_results_TBRDist.html)
>
> I found a similar issue in the r-packages archives (
> https://stat.ethz.ch/pipermail/r-package-devel/2018q3/002907.html). The
> suggestion in that case was that the issue may have been a false positive,
> a possibility that is consistent with a "HINT" in the output log.
>
> I optimistically suspect that this is the case here too: my package is an R
> wrapper to a mature C library, and the segmentation fault arises during a
> routine operation with simple input, not in some obscure corner case.  So
> question one is: how might I confirm that this is indeed a false positive?
>
> If it's not a false positive, then this raises the question of how I might
> reproduce it, as a Windows user without access to a machine running Fedora.
> rhub::check_with_sanitizers() uses debian, and returns 'success':
> https://builder.r-hub.io/status/TBRDist_1.0.0.9000.tar.gz-b965d74e18dd4bdc8e51e4254ee3699a
> Rocker (https://github.com/rocker-org/rocker) only offers a debian (not
> fedora) environment, so looks like it will not reproduce the error.
>
> Any thoughts would be gratefully received!

The error points to this spot:
https://github.com/ms609/uspr-r/blob/04ecc6f6d26d7db957dc7da2d7753e0cec040a92/tbr.h#L2973

If I'm reading this correctly, if the match happens at the beginning
of the loop, then this is decrementing an iterator to
sibling_pairs.begin(), which doesn't sound good. This can't really
have an impact, because there's a break afterwards, but the library
shouldn't be doing that anyway.

-- 
Iñaki Úcar