[llvm-dev] Intel MPX support (instrumentation pass similar to gcc's Pointer Checker)
Kostya Serebryany via llvm-dev
llvm-dev at lists.llvm.org
Thu Jan 28 11:29:06 PST 2016
I've recently played with the GCC implementation of pointer checker on a
my recent impressions are here:
(there is also some old pre-hardware content).
In short, I totally agree with what David says above: MPX is a disaster.
(Usual disclaimer: my opinion here is too biased)
I am glad that LLVM already has the support for MPX instructions, but I see
no good reason to add the MPX-based checker to LLVM.
Yes, it will allow us to detect intra-object overflows, something that asan can
not do by default
but it's not worth the extreme complexity of the MPX-based checker.
On Thu, Jan 28, 2016 at 9:14 AM, David Chisnall via llvm-dev <
llvm-dev at lists.llvm.org> wrote:
> On 28 Jan 2016, at 17:03, Dmitrii Kuvaiskii via llvm-dev <
> llvm-dev at lists.llvm.org> wrote:
> > Interestingly, my
> > preliminary experiments indicate that adding MPX bounds checking via
> > Pointer Checker in gcc is usually slower than using software-only
> > AddressSanitizer.
> This corresponds with other results that I have seen. The last time I
> looked at the output from gcc, it also did not generate pointer updates
> that were safe in the presence of concurrency (they must be bracketed in
> transactions if you want the MPX metadata and the pointer updates to be
> atomic) and the overhead of this is likely to be even more.
> I am particularly impressed with Intel for creating a hardware
> implementation that is both slower than a software-only version and can not
> (due to its fail-open policy being embedded in the hardware) be used for
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
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