On Mon, 27 Nov 2017, Jim Wilson wrote: > On 11/27/2017 12:21 AM, Richard Biener wrote: > > Let's formally deprecate any non-DWARF debugging format support > > in GCC 8 changes.html? > > I think we need to be careful about that. I've been looking at the stabs > support after I finished removing the sdb/coff debug info support. We have 3 > cpu targets that only support stabs (avr, pdp11, vax). We have two OS targets > that only support stabs, though in both cases the cpus do support dwarf and > hence they could switch. We have two embedded targets that support the > --with-stabs configure option. We have a few targets that might default to > stabs if used with old obsolete assembler versions that probably don't work > anymore anyways. And we have AIX which continues to use XCOFF_DEBUG which is > a variant of stabs, and shares some of the same code. We also have vms which > apparently uses a mixture of vms and dwarf2 debugging. Does that count as a > non-DWARF debugging format? > > I think a good first step would be to emit a compile-time warning if gcc was > configured to emit stabs by default. E.g. maybe something like > #if PREFERRED_DEBUGGING_TYPE == DBX_DEBUG > #warning "dbx/stabs debug info support is being deprecated" > #endif > in a popular header file. That gives maintainers a chance to fix their ports. > I was planning to propose this after gcc-8, but we could maybe add it to > gcc-8. Then maybe in the next version this changes to a #error, so you can't > build a gcc that emits stabs by default, but users can still get stabs with > -gstabs. We can then emit a run-time warning when a user uses -gstabs, and > then later a run-time error when -gstabs is used. That gives users a chance > to migrate before it breaks. Then we can remove -gstabs, careful to avoid > breaking xcoff support, until IBM agrees in the futility of continuing to > maintain it and lets us remove xcoff too.
I think we want to decomission -gstabs for all targets that do not default to it (or variants of it) and adjust documentation to reflect that -gstabs is unmaintained and deprecated. We also want to deprecate --with-stabs if there is an alternative, preferable emit a warning for this configure option for GCC 8 and remove support for GCC 9. I think embedded folks stick to STABS because of its smaller size, not because it is anywhere useful. Richard.
