https://gcc.gnu.org/bugzilla/show_bug.cgi?id=77589
--- Comment #4 from rguenther at suse dot de <rguenther at suse dot de> --- On Thu, 15 Sep 2016, jakub at gcc dot gnu.org wrote: > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=77589 > > Jakub Jelinek <jakub at gcc dot gnu.org> changed: > > What |Removed |Added > ---------------------------------------------------------------------------- > CC| |aldyh at gcc dot gnu.org, > | |rguenth at gcc dot gnu.org > > --- Comment #3 from Jakub Jelinek <jakub at gcc dot gnu.org> --- > I'm afraid this is similar to the DW_AT_string_length troubles (but not to the > direct reference to a DIE of some local variable, which can be besides the > hack > we have now solved using DWARF extension, but to the indirect one where we > only > have the hack which won't really work for LTO). > > In this case, when the FE fills in the array_descr_info, it fills in: > (gdb) p debug_generic_stmt (info->dimen[0].lower_bound) > *(D#1 + 32); > > $4 = void > (gdb) p debug_generic_stmt (info->dimen[0].upper_bound) > *(D#1 + 40); > > $5 = void > (gdb) p debug_generic_stmt (info->dimen[0].stride) > *(D#1 + 24) * span.0; > > The first two are representable just fine, > .uleb128 0x4 # DW_AT_lower_bound > .byte 0x97 # DW_OP_push_object_address > .byte 0x23 # DW_OP_plus_uconst > .uleb128 0x20 > .byte 0x6 # DW_OP_deref > and > .uleb128 0x4 # DW_AT_upper_bound > .byte 0x97 # DW_OP_push_object_address > .byte 0x23 # DW_OP_plus_uconst > .uleb128 0x28 > .byte 0x6 # DW_OP_deref > but the problem is with the stride, it refers to a local variable, but > obviously during early debug we don't really have location description for > that > variable. And like for DW_AT_string_lenght, DW_OP_call{2,4,_ref} isn't the > 100% answer here, because those expect the referenced DIE has DWARF expression > rather than location description. So we'd need DW_OP_variable_value or > something similar. So DW_OP_GNU_implicit_ptr doesn't work here? Not sure I understand how DW_OP_GNU_implicit_ptr works fully. That is, ... *(D#1 + 24) DW_OP_GNU_implicit_ptr <span.0> + 0 DW_OP_mul the examples in the specification always finish the dwarf expression with DW_OP_GNU_implicit_ptr which wouldn't be the case here.
