[Dwarf-discuss] Question about variable location in Dwarf

[Sebastian Krawczuk]

Jun,

You can almost blindly assume that this has to be (but not necessarily) 
a frame pointer register.  Unfortunately mapping between DWARF register 
IDs and H/W registers is compiler-centric.  For gcc (and some other 
compilers too) Reg #5 happens to be EBP ;)

Good luck!
Sebastian.

Jun Koi wrote:
> Hello,
>
> I am having some problem interpreting Dwarf format. I am trying to get
> the address of a local variable in my C program by analyzing the Dwarf
> format. Here is my simple code:
>
> .....
> int main()
> {
>         static char buffer[512];
>         struct old_utsname old;
> ....
> }
>
> I use dwarfdump on the debugged binary of my code, and get the below data:
>
> ....
> <1><  578>      DW_TAG_subprogram
>                 DW_AT_sibling               <655>
>                 DW_AT_external              yes(1)
>                 DW_AT_name                  main
>                 DW_AT_decl_file             1 /home/jun/projects/olduname.c
>                 DW_AT_decl_line             24
>                 DW_AT_type                  <208>
>                 DW_AT_low_pc                0x8048433
>                 DW_AT_high_pc               0x804854e
>                 DW_AT_frame_base            DW_OP_reg5
> <2><  605>      DW_TAG_variable
>                 DW_AT_name                  buffer
>                 DW_AT_decl_file             1 /home/bun/projects/olduname.c
>                 DW_AT_decl_line             25
>                 DW_AT_type                  <655>
>                 DW_AT_location              DW_OP_addr 0x80497c0
> <2><  625>      DW_TAG_variable
>                 DW_AT_name                  old
>                 DW_AT_decl_file             1 /home/bun/projects/olduname.c
>                 DW_AT_decl_line             26
>                 DW_AT_type                  <291>
>                 DW_AT_location              DW_OP_breg5-329
>
> ......
>
> So I understand that the (run-time) virtual address of the variable
> "buffer" is at 0x80497c0. But how can I get the virtual address of the
> variable "old"? It seems that I must get it by computing "DW_OP_breg5
> - 329"? But how can I get the value of DW_OP_breg5 in this case?
>
> I understand that DW_OP_breg5 is the value of a register, right? But
> what is that register? (ebp? I am on Intel x86)
>
> Thank you a lot,
> Jun
>
> _______________________________________________
> Dwarf-discuss mailing list
> Dwarf-discuss at lists.freestandards.org
> http://lists.freestandards.org/mailman/listinfo/dwarf-discuss
>   

-- 
Sebastian Krawczuk
OC Systems, Inc.
Office: 703-279-2770
Cell:   703-855-2323
Email:  syk at ocsystems.com

# make sense
make: 1254-002 Cannot find a rule to create target sense from dependencies.
Stop.