On 12/7/10 10:16 AM, Vincent De Bruyne wrote:> Hi,
>
> I'm a student who is going to make a countermeasure for dangling
> pointers in c for his thesis.
> I need to make my source transformation using llvm. Nobody in my
> university already used LLVM.
>
> I already read a some documentation about llvm but i'm still lost.
>
> Do there exist some " examples/Tutorials" for making small source
> transformations.
> Or is there somebody who can help me a bit to get started.
The LLVM Programmer's Manual
(http://llvm.org/docs/ProgrammersManual.html) and the Writing an LLVM
Pass Guide (http://llvm.org/docs/WritingAnLLVMPass.html) are good
documents on how to write transform and analysis passes that plug into
the LLVM opt tool.
Some of the passes in the SAFECode compiler
(http://safecode.cs.illinois.edu) are pretty simple and illustrate
simple tasks like instrumenting loads and stores or modifying calls to
functions. If you check out the mainline code, you can look at
lib/InsertPoolChecks/LoadStoreChecks.cpp,
lib/InsertPoolChecks/insert.cpp, and
lib/DebugInstrumentation/DebugInstrumentation.cpp for examples of
relatively simple passes.
That said, LLVM is not really suitable for Source to Source
transformations. While LLVM can convert C code to LLVM IR and back to C
code, it does not preserve comments, and the generated C code isn't
really designed to be readable by humans. I would normally recommend
Clang for Source to Source transformations, but in your case, working
with Clang's AST is probably more trouble than it's worth (from what I
hear). For dangling pointer detection, working on the LLVM IR is
probably easier.
As an aside, I work on SAFECode which (among other memory safety
guarantees) provides various protections for dangling pointer errors.
It enforces the points-to graph at run-time (as described in Dinakar
Dhurjati's PLDI 2006 paper) and includes a prototype implementation of
Dhurjati's et. al. dangling pointer detection method (DSN 2006). You
may want to take a look the CETS paper by Santosh Nagarakatte et. al.
(ISMM 2010) and Dinakar Dhurjati's PLDI 2006 paper (for which I can
provide an informal explanation if you don't like type-system proofs).
Links to these papers are at:
http://llvm.org/pubs/2006-DSN-DanglingPointers.html
http://www.cis.upenn.edu/~santoshn/ismm10-cets.pdf
http://llvm.org/pubs/2006-06-12-PLDI-SAFECode.html
SAFECode is publicly available at http://safecode.cs.illinois.edu. CETS
may be available from Santosh's website.
-- John T.
>
> Thx
> Vincent
>
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