On Wed, Nov 30, 2022 at 11:41:26PM +0000, Conor Dooley wrote: > From: Conor Dooley <conor.dooley@xxxxxxxxxxxxx> > > The RISC-V specs are permissive in what they allow as the ISA string, > but how we output this to userspace in /proc/cpuinfo is quasi uAPI. > > Formalise this as part of the uAPI, by documenting the list of rules > we use at this point in time. > > Signed-off-by: Conor Dooley <conor.dooley@xxxxxxxxxxxxx> > --- > I've not "tested" these docs. The NIPA-esque pwbot should go and > test it AFAICT. If it doesn't, I'll go add that. > --- > Documentation/riscv/uabi.rst | 42 ++++++++++++++++++++++++++++++++++++ > 1 file changed, 42 insertions(+) > > diff --git a/Documentation/riscv/uabi.rst b/Documentation/riscv/uabi.rst > index 21a82cfb6c4d..bc3c8ced644b 100644 > --- a/Documentation/riscv/uabi.rst > +++ b/Documentation/riscv/uabi.rst > @@ -3,4 +3,46 @@ > RISC-V Linux User ABI > ===================== > > +Misaligned accesses > +------------------- > + > Misaligned accesses are supported in userspace, but they may perform poorly. > + > +ISA string ordering in /proc/cpuinfo > +------------------------------------ > + > +The canonical order of ISA extension names in the ISA string is defined in > +chapter 27 of the unprivileged specification. > +The specification uses vague wording, such as should, when it comes to > +ordering, so for our purposes the following rules apply: > + > +#. Single-letter extensions come first, in "canonical order", so > + "IMAFDQLCBKJTPVH". > + > +#. All multi-letter extensions will be separated from other multi-letter > + extensions by an underscore. > + > +#. Additional standard extensions (starting with 'Z') will be sorted after > + single-letter extensions and before any higher-privileged extensions. > + > +#. The first letter following the 'Z' conventionally indicates the most > + closely related alphabetical extension category, IMAFDQLCBKJTPVH. > + If multiple 'Z' extensions are named, they should be ordered first by > + category, then alphabetically within a category. > + > +#. Standard supervisor-level extensions (starting with 'S') will be listed > + after standard unprivileged extensions. If multiple > + supervisor-level extensions are listed, they will be ordered > + alphabetically. > + > +#. Standard machine-level extensions (starting with 'Zxm') will be listed > + after any lower-privileged, standard extensions. If multiple > + machine-level extensions are listed, they will be ordered > + alphabetically. > + > +#. Non-standard extensions (starts with 'X') will be listed after all Ehh, it's always the read *after* sending something that I notice the inconsistency. This should be s/starts/starting/ for consistency. > + standard extensions. > + > +An example string following the order is: > + rv64imadc_zifoo_zigoo_zafoo_sbar_scar_zxmbaz_xqux_xrux > + > -- > 2.38.1 >
