[llvm-dev] Function call replacement (original) (raw)

zxhuan via llvm-dev llvm-dev at lists.llvm.org
Wed Mar 3 16:50:25 PST 2021

One example can be a constructor of a class, say class Foo, in C++. When you have a vector of Foo instances, the constructor will be called by the library function of vector. There are many such functions, that you can't know they are actually executed until the runtime.

Beside that, I have done some research today. This has to be done by modifying the class's vtable. I have manually modified the IR file and it works. But I just can't find an API function of LLVM to modify the vtable of the class.

On Wed, Mar 3, 2021 at 3:03 PM David Blaikie <dblaikie at gmail.com> wrote:

On Wed, Mar 3, 2021 at 11:55 AM zxhuan via llvm-dev <_ _llvm-dev at lists.llvm.org> wrote: Hi all,

I am trying to replace calls to a function, say foo() with calls to myfoo(). In the IR file, there is no call to foo(). However, foo() will be called during execution. Can't say I'm following here ^ there is no call to foo() but it is called during execution? Is it called indirectly (eg: void (*x)() = foo; x(); )? is the call in another module/not this IR file? I can't use the conventional way to do it (i.e. locate the call instruction, create a call site and then create a call to myfoo(), then replace all uses with the return value of myfoo()), because you can't locate the call instruction. So I tried to swap the name of foo() and myfoo(). However, this only results in the original function with the new name being called. I know I must have missed some steps, resulting in the reference to the original function still existing after the renaming. The question is, what is the missing step? Thank you so much for reading my description. I hope I make my question clear. Best, Jason

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