Passing callback function pointer to an enclave (Intel SGX)

App.cpp

void CallMe(int x) {
	printf("Num %d\n",x);
}

int main() {
	/* Setup enclave */
	sgx_enclave_id_t eid;
	sgx_status_t ret;
	sgx_launch_token_t token = { 0 };
	int token_updated = 0;

	ret = sgx_create_enclave(ENCLAVE_FILE, SGX_DEBUG_FLAG, &token,
			&token_updated, &eid, NULL);
	if (ret != SGX_SUCCESS) {
		cout << "sgx_create_enclave failed: 0x" << std::hex << ret << endl;
		return 1;
	}

	FunctionPointer ptr = { &CallMe };

	ecall_pass_func(eid, &ptr);

	sgx_destroy_enclave(eid);

}

Enclave.cpp

void ecall_pass_func(FunctionPointer *ptr){
	ptr->ptr(10);
}

enclave.edl

enclave {
   
    include "user_type.h"

    trusted {    
        public void ecall_pass_func([user_check] FunctionPointer *ptr);
        
    };
    
    untrusted {
    
    };
    
};

user_type.h

struct FunctionPointer{
	void (*ptr)(int);
};
typedef struct FunctionPointer FunctionPointer;

This approach won’t work if you pass class member function.