Fix Issue 10311 - GDB prints wrong value for variable updated from closure

[tramker]

https://issues.dlang.org/show_bug.cgi?id=10311

The main problem is how to get the offset data from toir.c to dwarf.c. I have modified struct Symbol to do this, not sure if it is the proper approach. Comment please.

[WalterBright]

A closure is implemented as a struct with fields for each variable. Would that work better?

[ibuclaw]

This seems to be correct based on what GDC does. We emit frames/closures as structs, and in the debug codegen alias the var decl to the field offset.

So in the following example:

auto outer()
{
  int val;
  int inner() { return val * 2; }
  return &inner;
}

We have the closure (at fbreg -40):

 <4><84>: Abbrev Number: 7 (DW_TAG_variable)
    <85>   DW_AT_name        : (indirect string, offset: 0xc5): __closptr
    <8d>   DW_AT_location    : 2 byte block: 91 58      (DW_OP_fbreg: -40)

The field in the closure (at position 8):

 <2><125>: Abbrev Number: 19 (DW_TAG_member)
    <126>   DW_AT_name        : val
    <130>   DW_AT_data_member_location: 8

And the variable proper which has it's location pointing to the offset in the closure.

 <4><73>: Abbrev Number: 6 (DW_TAG_variable)
    <74>   DW_AT_name        : val
    <7e>   DW_AT_location    : 5 byte block: 91 58 6 23 8       (DW_OP_fbreg: -40; DW_OP_deref; DW_OP_plus_uconst: 8)

@tramker - does this get emitted for parameters too? (You shouldn't need to).

[tramker]

I need more time on this issue, I'm closing for now.

[tramker]

Iain, I'm not sure what you mean by "in the debug codegen alias the var decl to the field offset" or how to do it, so if you can point me to the GDC source, it would be helpful.

[ibuclaw]

@tramker - I describe it in the post above. See the DW_AT_location. You are doing it in this PR.