Re: Reference to .debug_loc

[Daniel Jacobowitz <drow@mvista.com>]

On Fri, Feb 14, 2003 at 02:24:43PM -0500, Daniel Berlin wrote:
> 
> On Friday, February 14, 2003, at 10:26  AM, Daniel Jacobowitz wrote:
> 
> >On Fri, Feb 14, 2003 at 03:57:55PM +0100, Michal Ludvig wrote:
> >>Hi again,
> >>when location lists are in use, .debug_info looks like this:
> >>
> >>        .section        .debug_info
> >>        .long   0x187   # Length of Compilation Unit Info
> >>        .value  0x2     # DWARF version number
> >>        .long   .Ldebug_abbrev0 # Offset Into Abbrev. Section
> >>        .byte   0x8     # Pointer Size (in bytes)
> >>        .uleb128 0x1    # (DIE (0xb) DW_TAG_compile_unit)
> >>        .long   .Ldebug_line0   # DW_AT_stmt_list
> >>        .quad   .Letext0        # DW_AT_high_pc
> >>        .quad   .Ltext0 # DW_AT_low_pc
> >>        .byte   0x1     # DW_AT_language
> >>         [...]
> >>        .uleb128 0x3    # (DIE (0x50) DW_TAG_formal_parameter)
> >>        .long   .LASF2  # DW_AT_name: "value"
> >>        .byte   0x1     # DW_AT_decl_file
> >>        .byte   0x2     # DW_AT_decl_line
> >>        .long   0x8f    # DW_AT_type
> >>        .long   .LLST0-.Ldebug_loc0     # DW_AT_location
> >>
> >>So, the reference to .debug_loc on the last line of the example
> >>(DW_AT_location) is an offset within that section, ie. it's 0 (NULL) 
> >>for
> >>the first entry with a location list. However when I link several .o
> >>files together, each of them have DW_AT_location entries based at the
> >>same NULL.
> >>
> 
> Err, why?
> If they are in different files, it should be adjusting the offsets when 
> it merges the sections together, no?

Look at that operand.  It's the difference of two local labels - it
gets resolved at assembly time.

> >>Or is there another way?
> >
> >At a guess it should be like DW_AT_ranges:
> >        .long   .Ldebug_ranges0+0x0     # DW_AT_ranges
> >
> >I.E. dw2_asm_output_offset, rather than dw2_asm_output_delta, in GCC.
> >
> 
> It's supposed to be the offset from the beginning of the debug_loc 
> section.
> Will this do that?

I think so.  The result will be something like .Ldebug_ranges0 +
(.LLST0-.Ldebug_loc0).  If the assembler won't take that then we'll
have to track addresses for loclists the same as we do for rangelists.

-- 
Daniel Jacobowitz
MontaVista Software                         Debian GNU/Linux Developer