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bpf, docs: Editorial nits in instruction-set.rst

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This patch addresses a number of editorial nits including
spelling, punctuation, grammar, and wording consistency issues
in instruction-set.rst.

Signed-off-by: Dave Thaler <dthaler1968@gmail.com>
Acked-by: David Vernet <void@manifault.com>
Link: https://lore.kernel.org/r/20240405155245.3618-1-dthaler1968@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Dave Thaler 2024-04-05 08:52:45 -07:00 committed by Alexei Starovoitov
parent ba0cbe2bb4
commit 00d5d22a5b
1 changed files with 26 additions and 21 deletions
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47
Documentation/bpf/standardization/instruction-set.rst
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@ -43,7 +43,7 @@ a type's signedness (`S`) and bit width (`N`), respectively.
===== =========
For example, `u32` is a type whose valid values are all the 32-bit unsigned
numbers and `s16` is a types whose valid values are all the 16-bit signed
numbers and `s16` is a type whose valid values are all the 16-bit signed
numbers.
Functions
@ -108,7 +108,7 @@ conformance group means it must support all instructions in that conformance
group.
The use of named conformance groups enables interoperability between a runtime
that executes instructions, and tools as such compilers that generate
that executes instructions, and tools such as 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.
@ -181,10 +181,13 @@ A basic instruction is encoded as follows::
(`64-bit immediate instructions`_ reuse this field for other purposes)
**dst_reg**
destination register number (0-10)
destination register number (0-10), unless otherwise specified
(future instructions might reuse this field for other purposes)
**offset**
signed integer offset used with pointer arithmetic
signed integer offset used with pointer arithmetic, except where
otherwise specified (some arithmetic instructions reuse this field
for other purposes)
**imm**
signed integer immediate value
@ -228,10 +231,12 @@ This is depicted in the following figure::
operation to perform, encoded as explained above
**regs**
The source and destination register numbers, encoded as explained above
The source and destination register numbers (unless otherwise
specified), encoded as explained above
**offset**
signed integer offset used with pointer arithmetic
signed integer offset used with pointer arithmetic, unless
otherwise specified
**imm**
signed integer immediate value
@ -342,8 +347,8 @@ where '(u32)' indicates that the upper 32 bits are zeroed.
dst = dst ^ imm
Note that most instructions have instruction offset of 0. Only three instructions
(``SDIV``, ``SMOD``, ``MOVSX``) have a non-zero offset.
Note that most arithmetic instructions have 'offset' set to 0. Only three instructions
(``SDIV``, ``SMOD``, ``MOVSX``) have a non-zero 'offset'.
Division, multiplication, and modulo operations for ``ALU`` are part
of the "divmul32" conformance group, and division, multiplication, and
@ -370,10 +375,10 @@ etc. This specification requires that signed modulo use truncated division
a % n = a - n * trunc(a / n)
The ``MOVSX`` instruction does a move operation with sign extension.
``{MOVSX, X, ALU}`` :term:`sign extends<Sign Extend>` 8-bit and 16-bit operands into 32
bit operands, and zeroes the remaining upper 32 bits.
``{MOVSX, X, ALU}`` :term:`sign extends<Sign Extend>` 8-bit and 16-bit operands into
32-bit operands, and zeroes the remaining upper 32 bits.
``{MOVSX, X, ALU64}`` :term:`sign extends<Sign Extend>` 8-bit, 16-bit, and 32-bit
operands into 64 bit operands. Unlike other arithmetic instructions,
operands into 64-bit operands. Unlike other arithmetic instructions,
``MOVSX`` is only defined for register source operands (``X``).
The ``NEG`` instruction is only defined when the source bit is clear
@ -411,19 +416,19 @@ conformance group.
Examples:
``{END, TO_LE, ALU}`` with imm = 16/32/64 means::
``{END, TO_LE, ALU}`` with 'imm' = 16/32/64 means::
dst = htole16(dst)
dst = htole32(dst)
dst = htole64(dst)
``{END, TO_BE, ALU}`` with imm = 16/32/64 means::
``{END, TO_BE, ALU}`` with 'imm' = 16/32/64 means::
dst = htobe16(dst)
dst = htobe32(dst)
dst = htobe64(dst)
``{END, TO_LE, ALU64}`` with imm = 16/32/64 means::
``{END, TO_LE, ALU64}`` with 'imm' = 16/32/64 means::
dst = bswap16(dst)
dst = bswap32(dst)
@ -475,7 +480,7 @@ where 's>=' indicates a signed '>=' comparison.
gotol +imm
where 'imm' means the branch offset comes from insn 'imm' field.
where 'imm' means the branch offset comes from the 'imm' field.
Note that there are two flavors of ``JA`` instructions. The
``JMP`` class permits a 16-bit jump offset specified by the 'offset'
@ -494,25 +499,25 @@ Helper functions are a concept whereby BPF programs can call into a
set of function calls exposed by the underlying platform.
Historically, each helper function was identified by an address
encoded in the imm field. The available helper functions may differ
encoded in the 'imm' field. The available helper functions may differ
for each program type, but address values are unique across all program types.
Platforms that support the BPF Type Format (BTF) support identifying
a helper function by a BTF ID encoded in the imm field, where the BTF ID
a helper function by a BTF ID encoded in the 'imm' field, where the BTF ID
identifies the helper name and type.
Program-local functions
~~~~~~~~~~~~~~~~~~~~~~~
Program-local functions are functions exposed by the same BPF program as the
caller, and are referenced by offset from the call instruction, similar to
``JA``. The offset is encoded in the imm field of the call instruction.
A ``EXIT`` within the program-local function will return to the caller.
``JA``. The offset is encoded in the 'imm' field of the call instruction.
An ``EXIT`` within the program-local function will return to the caller.
Load and store instructions
===========================
For load and store instructions (``LD``, ``LDX``, ``ST``, and ``STX``), the
8-bit 'opcode' field is divided as::
8-bit 'opcode' field is divided as follows::
+-+-+-+-+-+-+-+-+
|mode |sz |class|
@ -580,7 +585,7 @@ instructions that transfer data between a register and memory.
dst = *(signed size *) (src + offset)
Where size is one of: ``B``, ``H``, or ``W``, and
Where '<size>' is one of: ``B``, ``H``, or ``W``, and
'signed size' is one of: s8, s16, or s32.
Atomic operations