[llvm-commits] Specification for Run-time Checks

[John Criswell]

On 5/14/12 10:37 AM, Nuno Lopes wrote:
> Hi John et al.,
>
> I read your proposal and all emails in the discussion.

To make things a little more concrete, I've thrown together an initial 
implementation of the simple bounds checks you described in your first 
email.  I implemented them using the SAFECode infrastructure (which is 
the basis of the proposal I wrote).

If anyone's up for trying it out, you can download it from 
http://sva.cs.illinois.edu/fastsc-llvm.tar.gz.

To compile it, just run the top-level configure in the llvm directory 
and type make.  The generated clang executable will be in 
llvm/projects/safecode/<build_type>/bin/clang.

To turn on the lightweight safety checks, use the -fmemsafety option.

The code uses just 4 LLVM passes:

1) One pass to insert checks:
http://llvm.org/viewvc/llvm-project/safecode/trunk/lib/InsertPoolChecks/LoadStoreChecks.cpp?view=log

2) One pass to optimize checks into fastlscheck when the bounds can be 
determined through local data-flow analysis:
http://llvm.org/viewvc/llvm-project/safecode/trunk/lib/OptimizeChecks/OptimizeChecks.cpp?view=log

3) One pass to remove the checks that you consider too slow:
http://llvm.org/viewvc/llvm-project/safecode/trunk/lib/OptimizeChecks/RemoveSlowChecks.cpp?view=log

4) One pass to inline the implementation of fastlscheck:
http://llvm.org/viewvc/llvm-project/safecode/trunk/lib/OptimizeChecks/InlineFastChecks.cpp?view=log

The first two passes have been in SAFECode for a long time.  The other 
two I wrote in the late afternoon and evening.  I think it took me about 
2 to 2.5 hours.

Obviously, I haven't put this code through much testing, but it seems to 
work on a trivial test case and doesn't break small programs.

I have other things that I need to work on, but I'll probably come back 
to it, do some more testing on it, and see if it's a feature that people 
want SAFECode to have.

Feedback is appreciated.

-- John T.