RE: [PATCH] MIPS function attributes for interrupt handlers

["Fu, Chao-Ying" <fu@mips.com>]

Nemet wrote:
> > +
> > +      /* If this interrupt is using a shadow register set, 
> we need to
> > +         get the stack pointer from the previous register set.  */
> > +      /* Trumping that concern, at least for the time 
> being, is that we
> > +         want the first four instructions of the interrupt 
> handler to be
> > +         the same for all handler functions.  This lets 
> there be cache lines
> > +         locked to those instructions, lowering the latency.  */
> > +      /* if (current_function_type == SRS_CONTEXT_SAVE) */
> > +	  fprintf (file, "\trdpgpr\t$sp, $sp\n");
> 
> You seems to be using MIPS32r2 instructions in the prologue.  
> I think this should be emitted in RTL.

  Ok.

> It seems that ipl7 implies two things: use the shadow 
> register set and that all interrupts should remain masked.  
> It seems the second can be useful even if the processor does 
> not support shadow registers.  One idea would be to split the 
> two and make them explicit (e.g. use_shadow_register_set and 
> keep_interrupts_masked attributes).
> 

  Yes. You are right.  Single and ipl0-ipl6 generate
same code that doesn't use shadow register sets, and allows nested
interrupts.  Ipl7 uses a shadow register set and doesn't allow
nested interrupts.
Using your two attributes allow a new combination.

> > +@item at_vector
> > +@cindex install interrupt handler at the address of 
> exception vector 
> > +on MIPS Using this attribute on MIPS indicates that the specific 
> > +interrupt handler should be located at the address of the 
> exception 
> > +vector (from 0 to 63).
> > +
> > +@smallexample
> > +void f ()  __attribute__ ((interrupt(single))) 
> > +__attribute__((at_vector (20))); @end smallexample
> > +
> > +The single interrupt handler f is installed at the 
> exception vectors 
> > +20 which section name is ".vector_20".
> 
> I think we shouldn't suggest here that we install this 
> function at a certain address but be clear that all this does 
> is to put the function into a named section.

  Ok.

Regards,
Chao-ying