[PATCH] Annotate our UB to sneak it past the sanitizers

[David Blaikie via llvm-commits]

On Fri, Feb 26, 2016 at 2:56 PM, Justin Bogner via llvm-commits <
llvm-commits at lists.llvm.org> wrote:

> Alexey Samsonov <vonosmas at gmail.com> writes:
> > What are the failures you observe? We're running an UBSan bootstrap on
> our
> > buildbot, and it's usually green:
> >
> http://lab.llvm.org:8011/builders/sanitizer-x86_64-linux-bootstrap/builds/11059
>
> Is that running without any blacklists? These are both the undefined
> behaviour in ilist_node and how we use it, ie:
>
>   runtime error: downcast of address XXX with insufficient space for an
> object of type 'llvm::MachineBasicBlock'
>
> This is because "Sentinel" in both of these functions is an
> ilist_half_node, which is certainly not large enough.
>
> It's certainly been necessary to blacklist MachineFunction on darwin
> since at least October, though the bug existed and wasn't caught by
> ubsan before that:
>
>   http://lists.llvm.org/pipermail/llvm-dev/2015-October/091115.html
>
> The one in MemorySSA just started hitting a month or so ago.
>

MemorySSA was only added a month or so ago, wasn't it? If it was added with
UB in it, it should probably have been removed/fixed, no?


>
> > On Thu, Feb 25, 2016 at 2:42 PM, Kostya Serebryany <kcc at google.com>
> wrote:
> >
> >> Sounds very scary.
> >> At the very least we should specify which flavor of UB we allow here
> (not
> >> just all of it)
>
> The macro expands to no_sanitize("undefined") right now - does
> no_sanitize take a more specific argument?
>
> > +1 I would prefer LLVM_NO_SANITIZE("kind") macro.
>
> Sure. I'll update the patch.
>
> >> And then comment why exactly we allow it.
> >>
> >
> > Or leave a link to PR for eventually fixing this UB.
>
> Apparently a PR for this never got filed, though I know Duncan's done
> some work towards fixing it. I filed llvm.org/PR26753 just now.
>
> >
> >> On Thu, Feb 25, 2016 at 1:19 PM, Justin Bogner <mail at justinbogner.com>
> >> wrote:
> >>
> >>> Attached patch silences -fsanitize=undefined wrt the UB we have for
> >>> ilist node sentinels. Okay to commit?
> >>>
> >>>
> >>
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