[LLVMdev] STM8 backend for Clang

[Andreas Färber]

Am 21.02.2011 um 02:44 schrieb Eli Friedman:

> On Sun, Feb 20, 2011 at 4:23 PM, Andreas Färber <andreas.faerber at web.de 
> > wrote:
>> The first issue I stumbled upon was that the Program Counter register
>> is 24 bits. [...]
>
> [...] if the only
> 24-bit register is the program counter, you could probably get away
> with pretending it's a 32-bit register.
>
>> Further, as pointer width I chose 16 bits since there currently seems
>> to be no way to distinguish between near and far pointers?
>
> LLVM doesn't support distinguishing between near and far pointers.
> Depending on how much work you want to put in and what exactly you're
> trying to build, you might be able to get away with just pretending
> all pointers are near and implementing __builtin_stm8_far_loadn() and
> __builtin_stm8_far_storen() intrinsics, though.

The example C code uses far pointers, e.g., to set up interrupt vectors:

typedef void @far (*interrupt_handler_t)(void);

struct interrupt_vector
{
   unsigned char interrupt_instruction;
   interrupt_handler_t interrupt_handler;
};

So I do need support for 24-bit pointers in the Clang frontend, in  
order for the struct to fill four bytes here.
Not sure how intrinsics could help there. I assume that @far is a non- 
standard keyword. Is it possible to derive a new language standard  
similar to GCC's --std=gnu99 to handle such extensions? The only guide  
I could find was on how to add an attribute...

Andreas