Hi Cary! On Thu, 16 May 2013 16:58:12 -0000, GCC Wiki <nore...@gcc.gnu.org> wrote: > The "DebugFission" page has been changed by CaryCoutant: > http://gcc.gnu.org/wiki/DebugFission?action=diff&rev1=18&rev2=19 > > = DWARF Extensions for Separate Debug Information Files = > > Updated January 24, 2013 > + > + The "Fission" project was started in response to the problems caused by > huge amounts of debug information in large applications. By splitting the > debug information into two parts at compile time -- one part that remains in > the .o file and another part that is written to a parallel .dwo ("DWARF > object") file -- we can reduce the total size of the object files processed > by the linker.
Yay, a quite noticeable link-time speedup! \o/
> + Fission is implemented in GCC 4.7, and requires support from recent
> versions of objcopy and the gold linker.
Is my understanding correct that the gold linker is not actually a
requirement -- at least nowadays? In my (very limited, so far) testing,
this also seems to work with ld.bfd. (I do see objcopy's --extract-dwo
and --split-dwo options being used in gcc/gcc.c:ASM_FINAL_SPEC, so I
suspect that's what "recent versions of objcopy" hints at?)
> + Use the {{{-gsplit-dwarf}}} option to enable the generation of split DWARF
> at compile time. This option must be used in conjunction with {{{-c}}};
> Fission cannot be used when compiling and linking in the same step.
According to the following -- admittedly very minimal -- testing, this is
not actually (no longer?) true?
$ [gcc] [...] -gsplit-dwarf
$ ls *.dwo
ccF9JYjE.dwo subroutines.dwo
$ gdb -q a.out
Reading symbols from a.out...done.
(gdb) list main
[...]
(gdb) quit
$ rm *.dwo
$ gdb -q a.out
Reading symbols from a.out...
warning: Could not find DWO CU subroutines.dwo(0x2d85cdd539df6900)
referenced by CU at offset 0x0 [in module [...]/a.out]
warning: Could not find DWO CU ccF9JYjE.dwo(0xa6936555a636518) referenced
by CU at offset 0x35 [in module [...]/a.out]
done.
(gdb) list main
warning: Could not find DWO CU subroutines.dwo(0x2d85cdd539df6900)
referenced by CU at offset 0x0 [in module [...]/a.out]
Have I been testing the wrong thing?
> + Use the gold linker's {{{--gdb-index}}} option ({{{-Wl,--gdb-index}}} when
> linking with gcc or g++) at link time to create the .gdb_index section that
> allows GDB to locate and read the .dwo files as it needs them.
Unless told otherwise, I'll re-word that to the effect that gold, and
usage of its --gdb-index option are optional.
Grüße
Thomas
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