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 + standard extensions. + +An example string following the order is: + rv64imadc_zifoo_zigoo_zafoo_sbar_scar_zxmbaz_xqux_xrux + -- 2.38.1
