Re: Reference to .debug_loc

[Daniel Berlin <dberlin@dberlin.org>]

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?

>> This time I realy can't see a way to find out at what position in the
>> resulting (ie. linked from several ones) .debug_loc should I start
>> reading for a given compilation unit.
>>
>> Should there be something more in the CU header? Something similar to
>> .long   .Ldebug_abbrev0 # Offset Into Abbrev. Section
>> For example
>> .long   .Ldebug_loc0 # Offset Into Loclist Section
>>
No.

>> 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?

> -- 
> Daniel Jacobowitz
> MontaVista Software                         Debian GNU/Linux Developer