Address of function in a module

I’m writing a module in C. I need to pass, as an argument to a SWI in another module, the address of a function in mine. I’ve used a recipe that worked for an application, but this gives the address as something like 0×81F8. Which would be fine if it were an app, but the module might be anywhere, and the address needs to be computed at run time. How do I do that in C?

Subtract 0×8000 and add the address of the header.

You might also be able to use inline assembler to do an ADR of the function.

Just cast the function to a uintptr_t e.g. _swix(..., (uintptr_t) mylittleponyfn) NB no parentheses following the function name. The module loader will sort out the relocation.

But is the other module guaranteed to be an APCS-32 caller?

You’ll surely want to go via a generic veneer otherwise when called your function won’t refer to the correct data?

Thanks, both. The address I want to give is the address of the veneer.

Pity the compiler doesn’t know what uintptr_t is…

Try “unsigned int”.

stdint.h is your friend

The address I want to give is the address of the veneer.

CMHG will make a header saying something like:

extern void module_veneer_ticker(void);

You can then call it like:

   r.r[0] = val;
   r.r[1] = (int)module_veneer_ticker;
   r.r[2] = (int)wsp;
   _kernel_swi(OS_CallAfter, &r, &r);

You will then be expected to write the handler, which is called in response to the code at that address being entered. The name is the same, with “_handler” suffixed.

_kernel_oserror *module_veneer_ticker_handler(_kernel_swi_regs *ir, void *pw)
{
   ...
}

This code taken from my MIDI module, if you need a working example.