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bpf, docs: Expand set of initial conformance groups

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This patch attempts to update the ISA specification according
to the latest mailing list discussion about conformance groups,
in a way that is intended to be consistent with IANA registry
processes and IETF 118 WG meeting discussion.

It does the following:
* Split basic into base32 and base64 for 32-bit vs 64-bit base
  instructions
* Split division/multiplication/modulo instructions out of base groups
* Split atomic instructions out of base groups

There may be additional changes as discussion continues,
but there seems to be consensus on the principles above.

v1->v2: fixed typo pointed out by David Vernet

v2->v3: Moved multiplication to same groups as division/modulo

Signed-off-by: Dave Thaler <dthaler1968@gmail.com>
Acked-by: David Vernet <void@manifault.com>
Link: https://lore.kernel.org/r/20240202221110.3872-1-dthaler1968@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Dave Thaler 2024-02-02 14:11:10 -08:00 committed by Alexei Starovoitov
parent e7f3187317
commit 2d9a925d0f
1 changed files with 36 additions and 12 deletions
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48
Documentation/bpf/standardization/instruction-set.rst
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@ -102,7 +102,7 @@ Conformance groups
An implementation does not need to support all instructions specified in this
document (e.g., deprecated instructions). Instead, a number of conformance
groups are specified. An implementation must support the "basic" conformance
groups are specified. An implementation must support the base32 conformance
group and may support additional conformance groups, where supporting a
conformance group means it must support all instructions in that conformance
group.
@ -112,12 +112,21 @@ that executes instructions, and tools as such compilers that generate
instructions for the runtime. Thus, capability discovery in terms of
conformance groups might be done manually by users or automatically by tools.
Each conformance group has a short ASCII label (e.g., "basic") that
Each conformance group has a short ASCII label (e.g., "base32") that
corresponds to a set of instructions that are mandatory. That is, each
instruction has one or more conformance groups of which it is a member.
The "basic" conformance group includes all instructions defined in this
specification unless otherwise noted.
This document defines the following conformance groups:
* base32: includes all instructions defined in this
specification unless otherwise noted.
* base64: includes base32, plus instructions explicitly noted
as being in the base64 conformance group.
* atomic32: includes 32-bit atomic operation instructions (see `Atomic operations`_).
* atomic64: includes atomic32, plus 64-bit atomic operation instructions.
* divmul32: includes 32-bit division, multiplication, and modulo instructions.
* divmul64: includes divmul32, plus 64-bit division, multiplication,
and modulo instructions.
* legacy: deprecated packet access instructions.
Instruction encoding
====================
@ -234,7 +243,8 @@ Arithmetic instructions
-----------------------
``BPF_ALU`` uses 32-bit wide operands while ``BPF_ALU64`` uses 64-bit wide operands for
otherwise identical operations.
otherwise identical operations. ``BPF_ALU64`` instructions belong to the
base64 conformance group unless noted otherwise.
The 'code' field encodes the operation as below, where 'src' and 'dst' refer
to the values of the source and destination registers, respectively.
@ -288,6 +298,10 @@ where '(u32)' indicates that the upper 32 bits are zeroed.
Note that most instructions have instruction offset of 0. Only three instructions
(``BPF_SDIV``, ``BPF_SMOD``, ``BPF_MOVSX``) have a non-zero offset.
Division, multiplication, and modulo operations for ``BPF_ALU`` are part
of the "divmul32" conformance group, and division, multiplication, and
modulo operations for ``BPF_ALU64`` are part of the "divmul64" conformance
group.
The division and modulo operations support both unsigned and signed flavors.
For unsigned operations (``BPF_DIV`` and ``BPF_MOD``), for ``BPF_ALU``,
@ -344,7 +358,9 @@ BPF_ALU64 Reserved 0x00 do byte swap unconditionally
========= ========= ===== =================================================
The 'imm' field encodes the width of the swap operations. The following widths
are supported: 16, 32 and 64.
are supported: 16, 32 and 64. Width 64 operations belong to the base64
conformance group and other swap operations belong to the base32
conformance group.
Examples:
@ -369,8 +385,10 @@ Examples:
Jump instructions
-----------------
``BPF_JMP32`` uses 32-bit wide operands while ``BPF_JMP`` uses 64-bit wide operands for
otherwise identical operations.
``BPF_JMP32`` uses 32-bit wide operands and indicates the base32
conformance group, while ``BPF_JMP`` uses 64-bit wide operands for
otherwise identical operations, and indicates the base64 conformance
group unless otherwise specified.
The 'code' field encodes the operation as below:
======== ===== === =============================== =============================================
@ -419,6 +437,9 @@ specified by the 'imm' field. A > 16-bit conditional jump may be
converted to a < 16-bit conditional jump plus a 32-bit unconditional
jump.
All ``BPF_CALL`` and ``BPF_JA`` instructions belong to the
base32 conformance group.
Helper functions
~~~~~~~~~~~~~~~~
@ -476,6 +497,8 @@ The size modifier is one of:
BPF_DW 0x18 double word (8 bytes)
============= ===== =====================
Instructions using ``BPF_DW`` belong to the base64 conformance group.
Regular load and store operations
---------------------------------
@ -520,8 +543,10 @@ by other BPF programs or means outside of this specification.
All atomic operations supported by BPF are encoded as store operations
that use the ``BPF_ATOMIC`` mode modifier as follows:
* ``BPF_ATOMIC | BPF_W | BPF_STX`` for 32-bit operations
* ``BPF_ATOMIC | BPF_DW | BPF_STX`` for 64-bit operations
* ``BPF_ATOMIC | BPF_W | BPF_STX`` for 32-bit operations, which are
part of the "atomic32" conformance group.
* ``BPF_ATOMIC | BPF_DW | BPF_STX`` for 64-bit operations, which are
part of the "atomic64" conformance group.
* 8-bit and 16-bit wide atomic operations are not supported.
The 'imm' field is used to encode the actual atomic operation.
@ -634,5 +659,4 @@ carried over from classic BPF. These instructions used an instruction
class of BPF_LD, a size modifier of BPF_W, BPF_H, or BPF_B, and a
mode modifier of BPF_ABS or BPF_IND. However, these instructions are
deprecated and should no longer be used. All legacy packet access
instructions belong to the "legacy" conformance group instead of the "basic"
conformance group.
instructions belong to the "legacy" conformance group.