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

[Alexey Samsonov via llvm-commits]

LGTM. I'd probably keep the amount of annotations to a minimum for now.

On Fri, Feb 26, 2016 at 5:09 PM, Justin Bogner <mail at justinbogner.com>
wrote:

> Alexey Samsonov <vonosmas at gmail.com> writes:
> > On Fri, Feb 26, 2016 at 2:56 PM, Justin Bogner <mail at justinbogner.com>
> 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?
> >
> > Hm, not really. cmake -DLLVM_USE_SANITIZER=Undefined expands to
> > "-fsanitize=undefined -fno-sanitize=vptr,function",
> > but this specific error seem to be coming from -fsanitize=object-size.
> >
> >> 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.
> >>
> >>> 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.
> >
> > Yes, you can use smth. like
> >   __attribute__((no_sanitize("signed-integer-overflow")))
>
> Here's an updated patch. This ones refers to the PR, renames the macro
> LLVM_NO_SANITIZE() and calls it with "object-size" instead of
> "undefined".
>
> Optionally, I could annotate the 7 other cases of this UB that aren't
> currently caught by running check-all under ubsan. I'm not sure which
> way's better - thoughts?
>
>


-- 
Alexey Samsonov
vonosmas at gmail.com
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