Re: [PATCH v2 3/4] libdw: Apply DWARF package file section offsets where appropriate

[Omar Sandoval <osandov@osandov.com>]

On Thu, Feb 22, 2024 at 04:53:19PM -0800, Omar Sandoval wrote:
> On Fri, Feb 16, 2024 at 04:00:47PM +0100, Mark Wielaard wrote:
> > Hi Omar,
> > 
> > On Wed, 2023-12-06 at 01:22 -0800, Omar Sandoval wrote:
> > > The final piece of DWARF package file support is that offsets have to be
> > > interpreted relative to the section offset from the package index.
> > > .debug_abbrev.dwo is already covered, so sprinkle around calls to
> > > dwarf_cu_dwp_section_info for the remaining sections: .debug_line.dwo,
> > > .debug_loclists.dwo/.debug_loc.dwo, .debug_str_offsets.dwo,
> > > .debug_macro.dwo/.debug_macinfo.dwo, and .debug_rnglists.dwo.  With all
> > > of that in place, we can finally test various libdw functions on dwp
> > > files.
> > 
> > So the offsets for DW_SECT_INFO, DW_SECT_TYPES and DW_SECT_ABBREV were
> > already taken into account when setting up a cu from a dwp.
> > 
> > With this patch __libdw_cu_str_off_base/str_offsets_base_off handles
> > DW_SECT_STR_OFFSETS which is used in dwarf_formstring and
> > dwarf_getmacros.
> > 
> > __libdw_cu_ranges_base handles DW_SECT_RNGLISTS, which is used by
> > dwarf_ranges. And __libdw_formptr has a special case for
> > DW_FORM_sec_offset for IDX_debug_ranges && version < 5 && unit_type ==
> > DW_UT_split_compile to also uses __libdw_cu_ranges_base.
> > 
> > __libdw_cu_locs_base handles DW_SECT_LOCLISTS which is used in
> > dwarf_getlocation through initial_offset. I do wonder why the special
> > case in __libdw_formptr isn't needed here too.
> > 
> > dwarf_getmacros handles DW_SECT_MACRO through get_offset_from. And when
> > the macros need to refer to the line table, it also handles
> > DW_SECT_LINE.
> > 
> > Don't we also need to handle DW_SECT_LINE in dwarf_getsrclines and
> > dwarf_next_lines when looking for DW_AT_stmt_list?
> 
> .debug_line is the odd one out in split DWARF: the skeleton file
> contains the full .debug_line, and the DWO or DWP files have a skeleton
> .debug_line.dwo that only contains the directory and file name tables
> (for DW_AT_file and macro info to reference). dwarf_getsrclines and co.
> read from the skeleton file, not the DWP file, meaning they shouldn't
> use DW_SECT_LINE.

Ah, I guess you can call dwarf_getsrclines/dwarf_next_lines on the dwp
file itself, where DW_SECT_LINE may be applicable. I need to think about
that some more...