Re: support for compilation units with discontiguous address ranges? (.debug_ranges)

[Daniel Berlin <dan@cgsoftware.com>]

Jim Blandy <jimb@zwingli.cygnus.com> writes:

> Brian Grant <grant@transmeta.com> writes:
>> Has anyone implemented dwarf2 support in gdb for compilation units with 
>> discontiguous ranges of addresses?
> 
> No.  Patches are welcome!
> 
>> gcc 3.x doesn't seem to produce .debug_ranges and gdb 5.0 doesn't
>> read it at all. gdb also seems to ignore .debug_aranges.
> 
> That's right.
> 
>> What currently happens in gdb is that all functions in .text1 
>> and .text2 at addresses between foo() and bar() are attributed
>> the file and line number of the last line of foo(). Their real,
>> accurate line-number info is overshadowed completely.
> 
> Right --- GDB misidentifies which compilation unit they belong to, so
> it never looks at the right compilation units' line tables.
> 
>> I noticed that gcc doesn't produce DW_AT_low_pc/high_pc fields for
>> foobar.c, as it normally would for a DW_TAG_compilation_unit record,
>> where all functions in the compilation unit were in the same
>> section.
> 
> Right, that's as required by the Dwarf 2 spec:
> 
>         The presence of low and high pc attributes in a compilation
>         unit entry imply that the code generated for that compilation
>         unit is contiguous and exists totally within the boundaries
>         specified by those two attributes.  If that is not the case,
>         no low and high pc attributes should be produced.
> 
> The Dwarf 2.1 spec says something similar.
> 
>> Does anyone know of a workaround for this problem?
> 
> I can only think of two options:
> 
> 1) Don't do that.  Put functions that need to go in separate segments
>    in separate .c files.
> 
> 2) Implement DW_AT_ranges support in GCC and GDB.

I have the first part of this done.
I just haven't submitted the patch yet, because i haven't had time to
update hte new dwarf2 reader to support it.


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