On Dec 19, 2007, "Daniel Berlin" <[EMAIL PROTECTED]> wrote:
> On 12/18/07, Alexandre Oliva <[EMAIL PROTECTED]> wrote: >> Dwarf enables arbitrary value expressions too. > Well, uh, no. > The only way to directly specify the value of a variable is for > constants. DW_AT_const_value does not allow location descriptions. DW_AT_const_value is irrelevant for location lists. It's DW_OP_* that I'm talking about. That said... I can't find any more the equivalent of DW_CFA_val_expression in DW_OP_*s that could be used in location expressions. I just *knew* it was there, but I guess I just imagined it. This is embarrassing. At this point, there are three options available: - go back to the drawing board - discard altogether expressions that don't represent lvalues (maybe don't even keep track of them) - introduce a DWARF extension that enables value expressions to be used in location lists (say DW_OP_value, DW_OP_temp_location, or even DW_OP_self_location (*)) (*) maps value to a virtual location that, if dereferenced, evaluates to the value. Could be "easily" implemented through a virtual out-of-range base address, plus the offset that represents the value on dereference, but there are many other ways to implement this in debug information consumers. > I'm still curious where you think it describes value expressions for > variables other than constants Me too :-) :-( Thanks for drawing my attention to this incorrect assumption I made about DWARF location lists. > i'd support such an extension Cool. Do you happen to know the procedure to propose DWARF standard extensions? -- Alexandre Oliva http://www.lsd.ic.unicamp.br/~oliva/ FSF Latin America Board Member http://www.fsfla.org/ Red Hat Compiler Engineer [EMAIL PROTECTED], gcc.gnu.org} Free Software Evangelist [EMAIL PROTECTED], gnu.org}
