[llvm-dev] How does sanitizers in compiler-rt work?

[Dipanjan Das via llvm-dev]

Hi Vedant,

Thanks for the pointers. Please find my replies inline.

On 16 June 2017 at 14:48, Vedant Kumar <vsk at apple.com> wrote:

>
> On Jun 16, 2017, at 4:11 AM, Dipanjan Das via llvm-dev <
> llvm-dev at lists.llvm.org> wrote:
>
>
> Can anybody give me any pointer on how compiler-rt, especially the
> sanitizers work? Do they operate on IR as any other LLVM pass? Or are they
> integral part of the frontend itself? I couldn't spot any documentation on
> the internals of compiler-rt project? What happens (sequence of actions)
> when I pass -fsanitizer=dataflow to clang?
>
>
> Passing -fsanitize=dataflow tells clang to insert the dataflow sanitizer's
> instrumentation pass into the normal compilation pipeline. The
> instrumentation occurs at the LLVM IR level. The pass may insert calls into
> runtime functions which are provided by compiler-rt. Therefore, in order to
> link a program compiled with -fsanitize=dataflow, the appropriate runtime
> library from compiler-rt is required.
>
>
> Precisely, I intend to alter the behaviour of DFSan to suit my need.
>
>
> What is your need, exactly?
>
>
Instead of manually inserting the dfsan_create_label() and
dfsan_set_label() calls in the source, I want to automatically insert those
calls in the IR for all the input variables in scanf(). I intend to run the
DFsan pass afterwards, thus instrumenting the IR further as required.


> Therefore, I need to know how it gets integrated in the tool-chain.
> Initially, my idea was to insert the dfsan_set_label() calls to the IR and
> pass it to DFSan. However, I am not sure if it's designed to run on the
> source only, not on IR.
>
>
> You should take a look at lib/Transforms/Instrumentation/DataFlowSanitizer.cpp.
> There doesn't appear to be much done at the source level.
>
> best,
> vedant
>
>
> --
>
> Thanks & Regards,
> Dipanjan
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>
>


-- 

Thanks & Regards,
Dipanjan
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