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

[Jim Blandy <jimb at zwingli dot cygnus dot com>]

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.