Register function from pointer

[dzonerzy]

Hi,

I have a DLL which export a pointer, this pointer points to a function I need to call, at first I tried with

purego.RegisterFunctionLib(&fnc, handle_lib, "callui")

But obviously this way I was calling the pointer itself rather than what this one is pointing to

then I tried

var fnc uintptr
purego.RegisterFunctionLib(&fnc, handle_lib, "callui")

var callui func(code int) int
purego.RegisterFunc(&callui, fnc)

But RegisterFunctionLib doesn't allow me register something to a uintptr handle it expect a function pointer and fnc is declared as uintptr

Now I'm trying

var fnc func()
purego.RegisterFunctionLib(&fnc, handle_lib, "callui")

var callui func(code int) int
purego.RegisterFunc(&callui, uintptr(unsafe.Pointer(&fnc)))

But I'm crashing I haven't yet analyzed the crash but I suspect that uintptr(unsafe.Pointer(&fnc)) is not returning what I want.

How am I supposed to do this?

[TotallyGamerJet]

On Unix you'd use Dlsym and then dereference the pointer. On windows you'd use GetProcAddress.

https://pkg.go.dev/github.com/ebitengine/purego?GOOS=darwin#Dlsym

[dzonerzy]

This would give me the pointer address same as what RegisterFunctionLib take and assign to the function, I wanted to avoid having to read the memory at that address to get the pointer value, Think would be handy to have such utility in purego.

Also I might be wrong but Dlsym as well as GetProcAddress won't dereference the pointer to my knowledge.

What GetProcAddress does is looping the export directory section find the export with the given name and return the associated address

[TotallyGamerJet]

Also I might be wrong but Dlsym as well as GetProcAddress won't dereference the pointer to my knowledge.

Correct you need to do that yourself. You'd then use that to call the function with either SyscallN or RegisterFunc.