On Wed, 9 Nov 2022 at 04:00, Palmer Dabbelt <pal...@rivosinc.com> wrote: > > On Tue, 08 Nov 2022 05:40:10 PST (-0800), christoph.muell...@vrull.eu wrote: > > On Mon, Nov 7, 2022 at 8:01 PM Palmer Dabbelt <pal...@rivosinc.com> wrote: > > > >> The docs say we take ISA strings, but that's never really been the case: > >> at a bare minimum we've required lower case strings, but there's > >> generally been some subtle differences as well in things like version > >> handling and such. We talked about removing the lower case requirement > >> in the last GNU toolchain meeting and we've always called other > >> differences just bugs. We don't have profile support yet, but based on > >> the discussions on the RISC-V lists it looks like we're going to have > >> some differences there as well. > > > > > >> So let's just stop pretending these are ISA strings. That's been a > >> headache for years now, if we're meant to just be ISA-string-like here > >> then we don't have to worry about all these long-tail ISA string parsing > >> issues. > >> > > > > You are right, we should first properly specify the -march string, > > before we talk about the implementation details of the parser. > > > > I tried to collect all the recent change requests and undocumented > > properties of the -march string and worked on a first draft specification. > > As the -march flag should share a common behavior across different > > compilers and tools, I've made a PR to the RISC-V toolchain-conventions > > repo: > > https://github.com/riscv-non-isa/riscv-toolchain-conventions/pull/26 > > > > Do you mind if we continue the discussion there? > > IMO trying to handle this with another RISC-V spec is a waste of time: > we've spent many years trying to follow the specs here, it's pretty > clear they're just not meant to be read in that level of detail. This > sort of problem is all over the place in RISC-V land, moving to a > different spec doesn't fix the problem.
Consider this repo as "hosted by RISC-V" and not as a RISC-V specification (e.g., it doesn't go through the lifecycle and never gets ratified/approved). Maybe that's easier to digest. Within RISC-V, some participants try hard to enforce a requirement for end-to-end implementations before a spec lands. This continually leads to some friction between the software community within RISC-V and those that "just need the specs done". If you see something in a spec going for public review (or even better: before it goes to public review and is at the committee sign-off stage) that is underspecified, let us know and we can request remedial action: the ABI effort in Zc is a good example of this. Anytime someone tries to skip these requirements, I point them to the 'bset' instruction (which—even though most people assume it—does not implement 'a | (1 << b)'; instead it implements 'a | (1 << (b & (XLEN-1)))'). Things like that get caught only if there are end-to-end software implementations to allow experimentation and review with various workloads and by a wide community. Philipp. > >> Link: https://lists.riscv.org/g/sig-toolchains/message/486 > >> > >> gcc/ChangeLog > >> > >> doc/invoke.texi (RISC-V): -march doesn't take ISA strings. > >> > >> --- > >> > >> This is now woefully under-documented, as we can't even fall back on the > >> "it's just an ISA string" excuse any more. I'm happy to go document > >> that, but figured I'd just send this along now so we can have the > >> discussion. > >> --- > >> gcc/doc/invoke.texi | 8 ++++---- > >> 1 file changed, 4 insertions(+), 4 deletions(-) > >> > >> diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi > >> index 94a2e20cfc1..780b0364c52 100644 > >> --- a/gcc/doc/invoke.texi > >> +++ b/gcc/doc/invoke.texi > >> @@ -28617,11 +28617,11 @@ Produce code conforming to version 20191213. > >> The default is @option{-misa-spec=20191213} unless GCC has been configured > >> with @option{--with-isa-spec=} specifying a different default version. > >> > >> -@item -march=@var{ISA-string} > >> +@item -march=@var{target-string} > >> @opindex march > >> -Generate code for given RISC-V ISA (e.g.@: @samp{rv64im}). ISA strings > >> must be > >> -lower-case. Examples include @samp{rv64i}, @samp{rv32g}, @samp{rv32e}, > >> and > >> -@samp{rv32imaf}. > >> +Generate code for given target (e.g.@: @samp{rv64im}). Target strings > >> are > >> +similar to ISA strings, but must be lower-case. Examples include > >> @samp{rv64i}, > >> +@samp{rv32g}, @samp{rv32e}, and @samp{rv32imaf}. > >> > >> When @option{-march=} is not specified, use the setting from > >> @option{-mcpu}. > >> > >> -- > >> 2.38.1 > >> > >>
