Re: [RFC] More compact (100x) -g3 .debug_macinfo (take 2)

[Jakub Jelinek <jakub@redhat.com>]

On Fri, Jul 15, 2011 at 12:15:48PM -0600, Tom Tromey wrote:
> >>>>> "Jakub" == Jakub Jelinek <jakub@redhat.com> writes:
> 
> Jakub> The patch below implements that slight change, in particular the
> Jakub> "4" suffixes from the op names were dropped,
> Jakub> DW_MACINFO_GNU_*_indirect have DW_FORM_udata and DW_FORM_strp
> Jakub> arguments now (i.e. DWARF_OFFSET_SIZE large) and
> Jakub> DW_MACINFO_GNU_transparent_include has DW_FORM_sec_offset
> Jakub> argument (i.e. again 4 bytes long for 32-bit DWARF and 8 bytes
> Jakub> long for 64-bit DWARF).  GCC assures that no merging will happen
> Jakub> between .debug_macinfo chunks with 32-bit and 64-bit DWARF by
> Jakub> adding the byte size in the comdat GROUP name.  I think that's
> Jakub> cleaner than hardcoding 4 bytes and not optimizing anything on
> Jakub> MIPS.
> 
> The .debug_macinfo section doesn't have any header describing its
> contents.  How would a consumer know which offset size to use?

The same way as it knows how to interpret the second operands of
DW_MACINFO_start_file.  They aren't meaningful without knowing what
.debug_line section they refer to.  For .debug_line, you need to remember
DW_AT_stmt_list of the CU that refers to the .debug_macinfo section
through DW_AT_macro_info, and you'd remember whether the referencing
CU is 32-bit DWARF or 64-bit DWARF.  And the producer would need to arange
that DW_MACINFO_GNU_transparent_include referenced chunks have the same
properties (i.e. same offset size, and, if they use DW_MACINFO_start_file,
also the same .debug_line).

	Jakub