On Wed, Oct 25, 2017 at 12:27 PM, asb at lowrisc dot org <gcc-bugzi...@gcc.gnu.org> wrote: > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82717 > > --- Comment #2 from Alex Bradbury <asb at lowrisc dot org> --- > (In reply to palmer from comment #1) >> Thanks Alex -- you're correct that this is a documentation/code mismatch. I >> just talked to Andrew and we think it's best to change the documentation. >> How does this sound: >> >> """ >> @item -mabi=@var{ABI-string} >> @opindex mabi >> Specify integer and floating-point calling convention. The default for this >> argument is system dependent, users who want a specific calling convention >> should specify one explicitly. The valid calling conventions are: ilp32, >> ilp32f, ilp32d, lp64, lp64f, and lp64d. >> """ > > I can see how a doc fix probably makes most sense at this point, as the > behaviour has been shipping in GCC for a while. Although I like the idea of > less typing it could be that inferring a default ABI from the target -march > was > a little too magic in the first place.
I think so. The desired mapping from ISA to ABI depends on the platform (e.g., -march=rv32imaf should probably use the ilp32 ABI on a Linux system because the standard libraries will be ilp32, but probably should use the ilp32f ABI on an embedded system). While we could define platform-specific mappings from -march to -mabi, things would get confusing quickly. Better, IMO, to specify -mabi explicitly. And of course this is mostly only a headache for cross-compilation; most native compilations will pass neither -mabi nor -march explicitly. > > I'd also suggest adding another sentence or two to explain that ilp32 and lp64 > describe soft-float calling conventions, while the f and d suffixes indicate > hard single or double precision floating point calling conventions.
