[llvm-dev] Possible UB in reading coverage mapping with compressed function names

[Vedant Kumar via llvm-dev]

If `Ptr = nullptr`, then ISTM that this would crash consistently unless `Size = 0`.

vedant

> On Apr 18, 2016, at 8:40 PM, Xinliang David Li <davidxl at google.com> wrote:
> 
> I will try to take a look at it some time this week.
> 
> David
> 
> On Mon, Apr 18, 2016 at 8:12 PM, Igor Kudrin <ikudrin.dev at gmail.com> wrote:
> Hi David, Vedant,
> 
> It looks like we might have UB somewhere connected with reading coverage mapping serialized in v2 format (with compressed function names).
> 
> I committed my patch, r266436, using the current format for .covmapping file, and then buildbots complained about it:
> * http://lab.llvm.org:8011/builders/sanitizer-x86_64-linux-fast/builds/11935/steps/check-llvm%20ubsan/logs/stdio
> * http://lab.llvm.org:8011/builders/sanitizer-x86_64-linux-bootstrap/builds/11460/steps/check-llvm%20ubsan/logs/stdio
> 
> I tried to reproduce the issue locally, but didn't succeed. Anyway, I've reapplied my patch (r266620) using the old format
> for .covmapping, and buildbots are happy now.
> 
> Could you take a look on that? Do you have any idea what might cause the problem?
> 
> Best regards,
> Igor Kudrin
>