[llvm-dev] Trace calls to memcpy

[Hideto Ueno via llvm-dev]

Hi Matt,

It looks to me that at least the function type doesn't match.
You have defined a type of `_Z12trace_memcpyPvS_m` as `() -> void` but
`memcpy` doesn't have that type.
You need to pass the same function type as `llvm.memcpy` to
`getOrInsertFunction`.

Regards,
Hideto


2020年3月12日(木) 22:15 Matt Fysh via llvm-dev <llvm-dev at lists.llvm.org>:

> Hello,
>
> I'm trying to use an LLVM Pass to trace calls to memcpy via
> instrumentation, but finding it quite difficult without having much
> knowledge of sound IR structure. Here's my FunctionPass thus far:
>
> // at the beginning of runOnFunction
> FunctionCallee hookFunc = M->getOrInsertFunction("_Z12trace_memcpyPvS_m",
> Type::getVoidTy(M->getContext()));
>
> // further in the same function
> for (BasicBlock &BB : F) {
>   for (Instruction &I : BB) {
>     if (isa<CallInst>(&I)) {
>       CallInst *CI = dyn_cast<CallInst>(&I);
>       Function* FC = CI->getCalledFunction();
>       StringRef SR = FC->getName();
>       if (SR == "llvm.memcpy.p0i8.p0i8.i64") {
>         CallInst* newInstr = dyn_cast<CallInst>(CI->clone());
>         newInstr->setCalledFunction(hookFunc);
>         newInstr->insertBefore(CI);
>       }
>     }
>   }
> }
>
> The issue arises when using `setCalledFunction`. If I remove that, it runs
> successfully and I end up with duplicate calls to memcpy - as expected.
>
> But when I leave it in, and run the pass with `opt`, I get the following
> error:
>
> LLVM ERROR: Broken function found, compilation aborted!
>
> Looking for any clues on how to fix... and would also appreciate  pointers
> in general about how I might learn the general concepts at play here.
>
> Thanks all,.
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