Re: RFA: Generate normal DWARF DW_LOC descriptors for non integer mode pointers

[Nick Clifton <nickc@redhat.com>]

Hi Jeff,

>>   Currently dwarf2out.c:mem_loc_descriptor() has some special case
>>   code to handle the situation where an address is held in a register
>>   whose mode is not of type MODE_INT.  It generates a
>>   DW_OP_GNU_regval_type expression which may later on be converted into
>>   a frame pointer based expression.  This is a problem for targets which
>>   use a partial integer mode for their pointers (eg the msp430).  In
>>   such cases the conversion to a frame pointer based expression could
>>   be wrong if the frame pointer is not being used.

> I may be missing something, but isn't it the transition to an FP 
> relative address rather than a SP relative address that's the problem 
> here?

Yes, I believe so.

> Where does that happen?  

I did not track it down.  But whilst I was searching for the cause I came
across the code that is modified by the patch.  Reading the code it seemed
obvious to me that the special case for handling non INT_MODE register modes
was not intended for pointers, and when I tried out a small patch it worked.

> Is it possible we've got the wrong DECL_RTL or somesuch?

I don't think so.  I am not familiar with this code myself, but the dump from 
the dwarf2 pass shows:

  (insn 5 2 6 (set (mem/c:HI (plus:PSI (reg/f:PSI 1 R1)
                (const_int 4 [0x4])) [1 c+0 S2 A16])
        (const_int 5 [0x5])) /work/sources/binutils/current/gdb/testsuite/gdb.base/advance.c:41 12 {movhi}
     (nil))

which to me pretty clearly shows that "c" is being stored at R1+4.

Cheers
  Nick