DWARF v4 .debug_line and .debug_frame formats

Roland McGrath roland@redhat.com
Thu Jun 17 00:06:00 GMT 2010


Are there any plans to make GCC and/or GAS emit the version 4 variants of
the .debug_line and/or .debug_frame formats?

The .debug_line version 4 format only adds the "maximum operations per
instruction" header field and associated logic, which is only meaningful
for VLIW machines (i.e. ia64--are there others?).  The old format is
specified such that it's always safe to use the new line-number program
operations without changing the header version field, so there is no real
reason to emit the new header format unless using the VLIW support.  But it
seems consistent with the rest of the behavior of -gdwarf-4 to emit the v4
format with that option.  I'd like to know when or if to expect ever to see
this format.

Similarly, the .debug_frame version 4 format only adds the address_size and
segment_size header fields.  I don't know if there are any GCC/GAS target
configurations that support segmented addresses for code so as to need
segment_size, or any that support using an address size other than that
implied by the ELF file class (or another container format's explicit or
implicit address size, or the architecture's implicit address size) so as
to need address_size.  But the same logic and questions apply as for
.debug_line even so.  OTOH, e.g. x86-64 -mcmodel=small could use
address_size 4 and save some space in the .debug_frame output.


Thanks,
Roland



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