[PATCH v2] bpf, docs: Formalize type notation and function semantics in ISA standard

* [PATCH v2] bpf, docs: Formalize type notation and function semantics in ISA standard
@ 2023-08-03  0:44 Will Hawkins
  2023-08-03  0:44 ` [Bpf] " Will Hawkins
  2023-08-04 22:04 ` Martin KaFai Lau
  0 siblings, 2 replies; 3+ messages in thread
From: Will Hawkins @ 2023-08-03  0:44 UTC (permalink / raw)
  To: bpf, bpf; +Cc: Will Hawkins

Give a single place where the shorthand for types are defined and the
semantics of helper functions are described.

Signed-off-by: Will Hawkins <hawkinsw@obs.cr>
---
 .../bpf/standardization/instruction-set.rst   | 79 +++++++++++++++++--
 1 file changed, 71 insertions(+), 8 deletions(-)

 Changelog:
   v1 -> v2:
	   - Remove change to Sphinx version
		 - Address David's comments
		 - Address Dave's comments

diff --git a/Documentation/bpf/standardization/instruction-set.rst b/Documentation/bpf/standardization/instruction-set.rst
index 655494ac7af6..fe296f35e5a7 100644
--- a/Documentation/bpf/standardization/instruction-set.rst
+++ b/Documentation/bpf/standardization/instruction-set.rst
@@ -10,9 +10,68 @@ This document specifies version 1.0 of the eBPF instruction set.
 Documentation conventions
 =========================
 
-For brevity, this document uses the type notion "u64", "u32", etc.
-to mean an unsigned integer whose width is the specified number of bits,
-and "s32", etc. to mean a signed integer of the specified number of bits.
+For brevity and consistency, this document refers to families
+of types using a shorthand syntax and refers to several expository,
+mnemonic functions when describing the semantics of opcodes. The range
+of valid values for those types and the semantics of those functions
+are defined in the following subsections.
+
+Types
+-----
+This document refers to integer types with a notation of the form `SN`
+that succinctly defines whether their values are signed or unsigned
+numbers and the bit widths:
+
+=== =======
+`S` Meaning
+=== =======
+`u` unsigned
+`s` signed
+=== =======
+
+===== =========
+`N`   Bit width
+===== =========
+`8`   8 bits
+`16`  16 bits
+`32`  32 bits
+`64`  64 bits
+`128` 128 bits
+===== =========
+
+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.
+
+Functions
+---------
+* `htobe16`: Takes an unsigned 16-bit number in host-endian format and
+  returns the equivalent number as an unsigned 16-bit number in big-endian
+  format.
+* `htobe32`: Takes an unsigned 32-bit number in host-endian format and
+  returns the equivalent number as an unsigned 32-bit number in big-endian
+  format.
+* `htobe64`: Takes an unsigned 64-bit number in host-endian format and
+  returns the equivalent number as an unsigned 64-bit number in big-endian
+  format.
+* `htole16`: Takes an unsigned 16-bit number in host-endian format and
+  returns the equivalent number as an unsigned 16-bit number in little-endian
+  format.
+* `htole32`: Takes an unsigned 32-bit number in host-endian format and
+  returns the equivalent number as an unsigned 32-bit number in little-endian
+  format.
+* `htole64`: Takes an unsigned 64-bit number in host-endian format and
+  returns the equivalent number as an unsigned 64-bit number in little-endian
+  format.
+* `bswap16`: Takes an unsigned 16-bit number in either big- or little-endian
+  format and returns the equivalent number with the same bit width but
+  opposite endianness.
+* `bswap32`: Takes an unsigned 32-bit number in either big- or little-endian
+  format and returns the equivalent number with the same bit width but
+  opposite endianness.
+* `bswap64`: Takes an unsigned 64-bit number in either big- or little-endian
+  format and returns the equivalent number with the same bit width but
+  opposite endianness.
 
 Registers and calling convention
 ================================
@@ -252,19 +311,23 @@ are supported: 16, 32 and 64.
 
 Examples:
 
-``BPF_ALU | BPF_TO_LE | BPF_END`` with imm = 16 means::
+``BPF_ALU | BPF_TO_LE | BPF_END`` with imm = 16/32/64 means::
 
   dst = htole16(dst)
+  dst = htole32(dst)
+  dst = htole64(dst)
 
-``BPF_ALU | BPF_TO_BE | BPF_END`` with imm = 64 means::
+``BPF_ALU | BPF_TO_BE | BPF_END`` with imm = 16/32/64 means::
 
+  dst = htobe16(dst)
+  dst = htobe32(dst)
   dst = htobe64(dst)
 
 ``BPF_ALU64 | BPF_TO_LE | BPF_END`` with imm = 16/32/64 means::
 
-  dst = bswap16 dst
-  dst = bswap32 dst
-  dst = bswap64 dst
+  dst = bswap16(dst)
+  dst = bswap32(dst)
+  dst = bswap64(dst)
 
 Jump instructions
 -----------------
-- 
2.40.1


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