Re: [avr] gas support for cfi info

[Richard Henderson <rth at redhat dot com>]

On 02/15/2011 02:44 PM, Petr HluzÃn wrote:
> In avr-tdep.c [1] near avr_dwarf_reg_to_regnum():
> /* Unfortunately dwarf2 register for SP is 32.  */

Excellent.  We're all on the same page for this.

> (I can't help you with the value for #define DWARF2_DEFAULT_RETURN_COLUMN  36)
> AFAIK there is no written ABI. Only the calling convention is
> documented (and only the easy cases), the rest is in gdb/gcc/binutils
> sources and people's heads.

As I recall, GCC defaults to using FIRST_PSEUDO_REGISTER for this,
so as to not overlap any hard registers.  I'll continue to so the same.

>   /* Avr-6 call instructions save 3 bytes.  */
>   switch (info.bfd_arch_info->mach)

Thanks.  That value is readily available in the assembler as well.

Anitha pointed out to me via gcc pr17994 that AVR uses post-decrement
for its pushes.  I had a brief read over the AVR insn manual, and it's
not crystal clear how multi-byte post-decrement pushes operate.

I've made an assumption that it happens as-if each byte is pushed
separately.  I.e.

  caller:           callee:
    save rN
    save rM
    trash    <- SP  hi(ret)  <- CFA
                    lo(ret)
                    trash    <- SP

This is the only way I can imagine that call insns interoperate with
byte push/pop insns.

All of which means that the return address is at a different offset
from the CFA than I originally thought.  This ought to be fixed in
the following.

Can someone please test these two patches and see if they actually
agree with the hardware?


r~

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