[LLVMdev] LLVM Valgrind

[John Criswell]

Javed Absar wrote:
> Hi: 
>
> I have been working on Valgrind [porting it to non-supported 
> architectures] and wanted to know what you guys think of Valgrind for 
> LLVM. 
> I haven't thought through fully myself - so wanted to get your inputs 
> before becoming rigid in my own opinion. 
>
> Original Valgrind works on object code - translating the asm to its 
> own IR [intermediate representation]. But for LLVM, probably putting 
> the valgrind 
> tool instrumentation [e.g. memcheck] as a pass [[i.e. using LLVM IR 
> itself] probably make more sense....

We have done just that in the SAFECode project 
(http://safecode.cs.illinois.edu).  To be more accurate, we took the old 
SAFECode research code, simplified it a bit (its more advanced features 
have experienced some bitrot; fixing that is on my TODO list), and 
enhanced it to use LLVM debugging information to report when a memory 
safety violation occurs.

SAFECode is a bit like a combination of Valgrind's memcheck and 
exp-ptrcheck tools in that it checks array indexing operations as well 
as loads and stores.  Additionally, SAFECode's array checking should be 
more accurate that Valgrind's because LLVM passes can determine the 
start address and size of stack objects and globals accurately whereas 
Valgrind's ptrcheck tool has to rely upon heuristics to determine this 
information.  SAFECode is also faster since it can employ static 
analysis and does not do dynamic binary translation. 

All of that said, Valgrind is a much more mature piece of software.  
Optimization can weaken SAFECode's ability to provide good debug info 
when used with LLVM 2.6, and testing with LLVM 2.7's improved debug info 
API isn't done yet.  Valgrind is also easier to use; SAFECode currently 
requires whole-program analysis, which means that you have to use it 
either on an LLVM bitcode file or through link-time optimization.

If you're interested in SAFECode, please feel free to try it out.  
SAFECode works with LLVM 2.6 and LLVM 2.7 (although the 2.7 support 
needs some improvement yet).  We have a mailing list 
(http://safecode.cs.illinois.edu/mailing.html) to which you can post 
questions.

-- John T.
>
> cheers 
> J.