On Mon, 2011-03-07 at 09:56 -0800, Roland McGrath wrote:
> $ echo > empty.c
> $ gcc -g -c empty.c
> $ dwarflint empty.o
> error: .debug_abbrev: couldn't load CU headers; assuming CUs are of
> latest DWARF flavor.
> error: .debug_abbrev: no abbreviations.
> error: .debug_info: data not found.
This produces zero-length .debug_info and .debug_line sections. There
is nothing wrong with that, though it would of course also be fine if
it didn't emit the ".section" directives at all.
It produces a .debug_abbrev section that is nothing but a single 0
byte. That is superfluous and it would be better if it omitted it
entirely, so I would recommend reporting that as a GCC bug. (Many
such files will add up to lots of wasted zero bytes in the linked
output.)
Bug and proposed patch:
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48041
> $ echo "static int empty;" > empty.c
> $ gcc -g -c empty.c
> $ eu-dwarflint empty.o
> error: .debug_line: table 0: sequence of opcodes not terminated with
> DW_LNE_end_sequence.
This produces a zero-length .debug_line section but a CU with a
DW_AT_stmt_list attribute pointing to its start. That is invalid
DWARF and hence a GCC bug. The place where DW_AT_stmt_list points
must have a valid line information header, even if that says it's an
empty table. I think what would be most correct here is to omit the
DW_AT_stmt_list attribute entirely from that CU DIE.
Actually, the header is there, but there are no tables.
Reported with possible patch:
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48045
But since the debug_line table header is actually there, dwarflint is
still not really happy. empty.o as produced by my patched gcc attached.
$ eu-dwarflint empty.o
warning: .debug_line: table 0: the file #1 `empty.c' is not used.
error: .debug_line: table 0: sequence of opcodes not terminated with
DW_LNE_end_sequence.
So maybe a better solution would be to just add a dummy end_sequence.
Cheers,
Mark