49 lines
1.9 KiB
ReStructuredText
49 lines
1.9 KiB
ReStructuredText
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.. SPDX-License-Identifier: GPL-2.0
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RISC-V Linux User ABI
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=====================
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ISA string ordering in /proc/cpuinfo
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------------------------------------
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The canonical order of ISA extension names in the ISA string is defined in
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chapter 27 of the unprivileged specification.
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The specification uses vague wording, such as should, when it comes to ordering,
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so for our purposes the following rules apply:
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#. Single-letter extensions come first, in canonical order.
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The canonical order is "IMAFDQLCBKJTPVH".
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#. All multi-letter extensions will be separated from other extensions by an
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underscore.
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#. Additional standard extensions (starting with 'Z') will be sorted after
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single-letter extensions and before any higher-privileged extensions.
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#. For additional standard extensions, the first letter following the 'Z'
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conventionally indicates the most closely related alphabetical
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extension category. If multiple 'Z' extensions are named, they will be
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ordered first by category, in canonical order, as listed above, then
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alphabetically within a category.
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#. Standard supervisor-level extensions (starting with 'S') will be listed
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after standard unprivileged extensions. If multiple supervisor-level
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extensions are listed, they will be ordered alphabetically.
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#. Standard machine-level extensions (starting with 'Zxm') will be listed
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after any lower-privileged, standard extensions. If multiple machine-level
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extensions are listed, they will be ordered alphabetically.
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#. Non-standard extensions (starting with 'X') will be listed after all standard
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extensions. If multiple non-standard extensions are listed, they will be
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ordered alphabetically.
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An example string following the order is::
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rv64imadc_zifoo_zigoo_zafoo_sbar_scar_zxmbaz_xqux_xrux
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Misaligned accesses
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-------------------
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Misaligned accesses are supported in userspace, but they may perform poorly.
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