In the DWARF info, what do they exactly mean by the DW_OP registers?

Question

I am trying to parse the DWARF info and then using that information get the local variables from a program using a pin tool. It is kind of like using pin as GDB on steroids. However, I am having troubles understanding what they mean by the registers they have for the local variables and allocated ones.

For example,

<2>< 1214>  DW_TAG_variable
    DW_AT_name                  mts
    DW_AT_decl_line             69
    DW_AT_type                  <90>
    DW_AT_location              DW_OP_breg4+44

I understand that, in order to get the data from the variable mts, I have to add 44 to some register, my problem is that I don't exactly which register they are talking about. How should I interpret this? I couldn't find anything online.

Another examples are the DW_OP_fbreg, DW_OP_breg5 and so on.

Anyone knows which registers are they talking about in an x86 context? Are they talking about ebp or esp? Thanks.

Answer 1

It's a symbolic register name. See the xxx_map_dwarf_register methods in WineHQ's source for:

• i386
• x86_64
• sparc
• arm

For example, DW_OP_breg4 is ESP on i386.

Also see the following if you haven't done so already.

• http://source.winehq.org/source/dlls/dbghelp/dwarf.c
• http://www.dwarfstd.org/doc/040408.1.html