Re: [rfa/6.0] Better handle unspecified CFI values

[Daniel Jacobowitz <drow@mvista.com>]

On Wed, Sep 10, 2003 at 12:47:54PM -0700, Richard Henderson wrote:
> On Mon, Sep 08, 2003 at 11:30:53PM -0400, Daniel Jacobowitz wrote:
> > We can only compute expressions
> > describing a memory location where the register is saved, not computed
> > values.
> 
> False.  See DW_CFA_expression.

True.  See DW_CFA_expression.

20. DW_CFA_expression

    The DW_CFA_expression instruction takes two operands: an unsigned
    LEB128 value representing a register number, and a DW_FORM_block
    value representing a DWARF expression. The required action is to
    establish the DWARF expression as the means by which the address in
    which the given register contents are found may be computed. The
    value of the CFA is pushed on the DWARF evaluation stack prior to
    execution of the DWARF expression.

    The DW_OP_call2, DW_OP_call4, DW_OP_call_ref and
    DW_OP_push_object_address DWARF operators (see Section 2.4.1)
    cannot be used in such a DWARF expression.

It computes "the address in which the given register contents are
found".  That's not ambiguous, and that's precisely how GCC uses it:
          _Unwind_SetGRPtr (context, i, (void *) val);


-- 
Daniel Jacobowitz
MontaVista Software                         Debian GNU/Linux Developer