Re: [GXemul-devel] GXemul 0.4 target PPC

[Anders G. <ga...@gm...>]

Ons 2008-07-16 klockan 09:12 +0200 skrev claude vittoria:
> Hi,
> 
> I implement Float instructions in PPC target with softfloat.
> 
> I m looking for an advice.
> 
> Each float instruction, need to test if FPU is enable. Thus I
> need the reel PC to launch fpu exception.
> In ic->args, I can only give 3 parameters (Rd, Ra, Rb). I don't
> want to provide the word in args and to decode it in the
> instruction.
> 
> I try to use this code.
> 
> int low_pc = ((size_t)cpu->cd.DYNTRANS_ARCH.next_ic - 
>        (size_t)cpu->cd.DYNTRANS_ARCH.cur_ic_page) 
>        sizeof(struct DYNTRANS_IC);   
>    cpu->pc &= ~((DYNTRANS_IC_ENTRIES_PER_PAGE-1) << 
>        DYNTRANS_INSTR_ALIGNMENT_SHIFT);  
>    cpu->pc += (low_pc << DYNTRANS_INSTR_ALIGNMENT_SHIFT);

There is already a macro for this, CHECK_FOR_FPU_EXCEPTION, in
cpu_ppc_instr.c. See e.g. the implementation of the fctiwz or fneg
instructions for example on how it is used.

..
> I get the pc+4 where is the instruction. It seems fine.
> 
> But I see your implementation of mtmsr and I don't understand why you
> don't use the code, above, when the instruction is executed. 
> I don't find argument...

mtmsr is not a good example to copy, because it contains a special hack.
fneg is better.

> Other question
> If I want to give a fourth argument in ic (arch ## _instr_call), I
> need to reduce the number of translated instructions ? I don't test
> this modification because I don't see all impacts...

If you really need to expand the number of arguments, then edit
PPC_N_IC_ARGS in src/include/cpu_ppc.h.


Anders