1.. SPDX-License-Identifier: GPL-2.0 2 3RISC-V Linux User ABI 4===================== 5 6ISA string ordering in /proc/cpuinfo 7------------------------------------ 8 9The canonical order of ISA extension names in the ISA string is defined in 10chapter 27 of the unprivileged specification. 11The specification uses vague wording, such as should, when it comes to ordering, 12so for our purposes the following rules apply: 13 14#. Single-letter extensions come first, in canonical order. 15 The canonical order is "IMAFDQLCBKJTPVH". 16 17#. All multi-letter extensions will be separated from other extensions by an 18 underscore. 19 20#. Additional standard extensions (starting with 'Z') will be sorted after 21 single-letter extensions and before any higher-privileged extensions. 22 23#. For additional standard extensions, the first letter following the 'Z' 24 conventionally indicates the most closely related alphabetical 25 extension category. If multiple 'Z' extensions are named, they will be 26 ordered first by category, in canonical order, as listed above, then 27 alphabetically within a category. 28 29#. Standard supervisor-level extensions (starting with 'S') will be listed 30 after standard unprivileged extensions. If multiple supervisor-level 31 extensions are listed, they will be ordered alphabetically. 32 33#. Standard machine-level extensions (starting with 'Zxm') will be listed 34 after any lower-privileged, standard extensions. If multiple machine-level 35 extensions are listed, they will be ordered alphabetically. 36 37#. Non-standard extensions (starting with 'X') will be listed after all standard 38 extensions. If multiple non-standard extensions are listed, they will be 39 ordered alphabetically. 40 41An example string following the order is:: 42 43 rv64imadc_zifoo_zigoo_zafoo_sbar_scar_zxmbaz_xqux_xrux 44 45Misaligned accesses 46------------------- 47 48Misaligned accesses are supported in userspace, but they may perform poorly. 49