[LLVMdev] [cfe-dev] Instrumenting all va_arg invocations

[John Criswell]

On 7/31/12 11:47 AM, Evgeniy Stepanov wrote:
> Hi,
>
> I'm looking for a way to add instrumentation that handles all function
> arguments, one by one. With variable argument lists, this can only be
> done at the place of va_arg() call. Unfortunately, Clang lowers va_arg
> into platform-specific code in the frontend, and I can't find a good,
> reliable way to figure it out in our LLVM pass.
>
> I've tried adding a special case of TBAA info to the instruction that
> calculates the address of the next argument, but this metadata gets
> lost in some of the code transformations at -O1 and higher. Anyway,
> this seems like an abuse of TBAA.
>
> There seem to be a number of dirty ways this can be done, like passing
> the "interesting" address to a fake external function that can be
> recognized in the LLVM pass and replaced with the instrumentation
> code.
>
> Is there a good way to mark a certain %temp in the frontend to assist
> instrumentation?

There was a patch to clang awhile ago that added an option to emit 
vararg intrinsics instead of platform-specific code.  You might try 
searching for it through the archives.

-- John T.

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