Issue logging within an embedded C function - simics

Question

I'd like to generate logging messages from within a C function embedded in a DML method. Take the example code below where the fib() function is called from the write() method of the regs bank. The log methods available to C all require a pointer to the current device.
Is there a way to get the device that calls the embedded function? Do I need to pass the device pointer into fib()?
dml 1.2;
device simple_embedded;
parameter documentation = "Embedding C code example for"
+ " Model Builder User's Guide";
parameter desc = "example of C code";
extern int fib(int x);
bank regs {
register r0 size 4 #0x0000 {
parameter allocate = false;
parameter configuration = "none";
method write(val) {
log "info": "Fibonacci(%d) = %d.", val, fib(val);
}
method read() -> (value) {
// Must be implemented to compile
}
}
}
header %{
int fib(int x);
%}
footer %{
int fib(int x) {
SIM_LOG_INFO(1, mydev, 0, "Generating Fibonacci for %d", x);
if (x < 2) return 1;
else return fib(x-1) + fib(x-2);
}
%}
I want to log from an embedded C function.

Answer 1

I solved this by passing the Simics conf_object_t pointer along to C. Just like implied in the question.
So you would use:
int fib(conf_object_t *mydev, int x) {
SIM_LOG_INFO(1, mydev, 0, "Generating Fibonacci for %d", x);
}
And
method write(val) {
log "info": "Fibonacci(%d) = %d.", val, fib(dev.obj,val);
}

Answer 2

Jakob's answer is the right one if your purpose is to offload some computations to C code (which makes sense in many situations, like when functionality is implemented by a lib).
However, if you just want a way to pass a callback to an API that asks for a function pointer, then it is easier to keep the implementation within DML and use a method reference, like:
method init() {
SIM_add_notifier(obj, trigger_fib_notifier_type, obj, &trigger_fib,
&dev.regs.r0.val);
}
method trigger_fib(conf_object_t *_, lang_void *aux) {
value = *cast(aux, uint64 *);
local int result = fib(value);
log info: "result: %d", result;
}
method fib(int x) -> (int) {
log info: "Generating Fibonacci for %d", x;
if (x < 2) return 1;
else return fib(x-1) + fib(x-2);
}