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| author | Palmer Dabbelt <palmer@rivosinc.com> | 2023-01-19 16:39:53 -0800 |
|---|---|---|
| committer | Palmer Dabbelt <palmer@rivosinc.com> | 2023-01-19 16:41:04 -0800 |
| commit | 61a9b7129070e07c207d89fffbce577223507327 (patch) | |
| tree | 780873ef048723b9c4668c38463facdee9aebf29 /Documentation/riscv | |
| parent | ae4d39f753080aff01830a607c22e5abc6012f41 (diff) | |
| parent | f07b2b3f9d47fea308af3ae05613b6b4801e68a3 (diff) | |
Merge patch series "Putting some basic order on isa extension lists"
This cleans up the ISA string handling to more closely match a version
of the ISA spec. This is visible in /proc/cpuinfo and the ordering
changes may break something in userspace, but these orderings have
changed before without issues so with any luck that's still the case.
This also adds documentation so userspace has a better idea of what is
intended when it comes to compatibility for /proc/cpuinfo, which should
help everyone as this will likely keep changing.
* b4-shazam-merge:
Documentation: riscv: add a section about ISA string ordering in /proc/cpuinfo
RISC-V: resort all extensions in consistent orders
RISC-V: clarify ISA string ordering rules in cpu.c
Link: https://lore.kernel.org/r/20221205144525.2148448-1-conor.dooley@microchip.com
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
Diffstat (limited to 'Documentation/riscv')
| -rw-r--r-- | Documentation/riscv/uabi.rst | 42 |
1 files changed, 42 insertions, 0 deletions
diff --git a/Documentation/riscv/uabi.rst b/Documentation/riscv/uabi.rst index 21a82cfb6c4d..2ebec4c52230 100644 --- a/Documentation/riscv/uabi.rst +++ b/Documentation/riscv/uabi.rst @@ -3,4 +3,46 @@ RISC-V Linux User ABI ===================== +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. + The canonical order is "IMAFDQLCBKJTPVH". + +#. All multi-letter extensions will be separated from other extensions by an + underscore. + +#. Additional standard extensions (starting with 'Z') will be sorted after + single-letter extensions and before any higher-privileged extensions. + +#. For additional standard extensions, the first letter following the 'Z' + conventionally indicates the most closely related alphabetical + extension category. If multiple 'Z' extensions are named, they will be ordered + first by category, in canonical order, as listed above, 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 (starting with 'X') will be listed after all standard + extensions. If multiple non-standard extensions are listed, they will be + ordered alphabetically. + +An example string following the order is:: + + rv64imadc_zifoo_zigoo_zafoo_sbar_scar_zxmbaz_xqux_xrux + +Misaligned accesses +------------------- + Misaligned accesses are supported in userspace, but they may perform poorly. |