Re: [avr] gas support for cfi info

["Petr Hluzín" <petr.hluzin@gmail.com>]

On 15 February 2011 20:03, Richard Henderson <rth@redhat.com> wrote:
> On 02/15/2011 09:41 AM, Richard Henderson wrote:
>> On 02/13/2011 07:10 AM, Petr Hluzín wrote:
>>> http://xfree86.cygwin.ru/ml/binutils/2010-08/msg00109.html
>>
>> I'll agree that a better error message would be helpful.
>>
>> To answer a question within that message:
>>
>>> By the way: Why AVR target does not understand CFI? What needs to be
>>> done in binutils? And in GDB?
>>
>>   TARGET_USE_CFIPOP
>>   DWARF2_DEFAULT_RETURN_COLUMN
>>   DWARF2_CIE_DATA_ALIGNMENT
>>   DWARF2_LINE_MIN_INSN_LENGTH
>>
>> are the macros that need to be defined,
>>
>>   tc_cfi_frame_initial_instructions
>>
>> may be required depending on what the state of the unwind
>> info incoming to a function.  Have a look at tc-i386.c,
>> tc_x86_frame_initial_instructions for a typical stack-based
>> call mechanism.
>>
>> For the nearly related task of dwarf2 line numbers, you need
>> a call to dwarf2_emit_insn emitted immediately before each
>> insn is added to the frags.  Again, see tc-i386.c for ideas.
>
> To follow up on myself, it appears as if avr already has dwarf2
> line number support, and only needs a few things in order to
> enable cfi support.
>
> CC'd to gcc and gdb because the dwarf2 register numbers for SP
> and the return address column need to be coordinated.  This is
> part of the target's ABI.

In avr-tdep.c [1] near avr_dwarf_reg_to_regnum():
/* Unfortunately dwarf2 register for SP is 32.  */

(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.

> I've left a ??? marker for when AVR_3_BYTE_PC would be true in
> gcc; I haven't tracked down how that maps into the assembler,
> or even if there is a simple mapping.

In avr_gdbarch_init() in avr-tdep.c [1]:
  /* Avr-6 call instructions save 3 bytes.  */
  switch (info.bfd_arch_info->mach)
    ...
    case bfd_mach_avr6:
      call_length = 3;
      break;

[1] http://sourceware.org/cgi-bin/cvsweb.cgi/~checkout~/src/gdb/avr-tdep.c?rev=1.128&content-type=text/plain&cvsroot=src

-- 
Petr Hluzin