Re: Request to merge Undefined Behavior Sanitizer in

[Jeff Law <law at redhat dot com>]

On 07/25/2013 04:40 PM, Joseph S. Myers wrote:
> On Thu, 25 Jul 2013, Marek Polacek wrote:
>
> > So far it sanitizes division-by-zeros, shifts and
> > __builtin_unreachable calls.  This is of course far from being
> > complete; I intend to write more features during this 4.9 stage.
>
> Such as everything needed for it to replace -ftrapv (for -ftrapv to become
> an alias for an appropriate subset of this option)?
I'm guessing Marek would probably start with looking to provide feature 
parity with LLVM's -fsanitize=undefined which is defined as:

-fsanitize=undefined: Fast and compatible undefined behavior checker. 
Enables the undefined behavior checks that have small runtime cost and 
no impact on address space layout or ABI. This includes all of the 
checks listed below other than unsigned-integer-overflow.

So I wouldn't necessarily expect ubsan, at least in the near future, to 
catch the -ftrapv stuff.  Though it's something that might be able to be 
added at some point.


> What happens if you bootstrap with this enabled - do whatever failures
> appear look like genuine bugs?  Running the testsuite with a compiler
> built with this option?  Running the testsuite with this option used when
> compiling all these tests.  I guess that initially a bootstrap with this
> option may fail because of existing bugs, and so the other tests mentioned
> can't yet be run - but using this option on GCC itself, and making sure
> that as far as possible it doesn't break compiling things or change
> diagnostics generated at compile time, seem like good goals.
Note that the instrumentation happens in c-family/ so we might not be 
fully instrumenting what comes out of the C++ front-end.  However, if 
we're getting a reasonable amount of sanitization, it'd be real 
interesting to track down any failures that trigger for bootstraps.

There are some projects out there that using ubsan (SpiderMonkey for 
example) from LLVM to root out issues.

Jeff