Dave Thaler wrote:
> From: Dave Thaler <dthaler@xxxxxxxxxxxxx>
>
> Add extended call instructions. Since BPF can be used in userland
> or SmartNICs, this uses the more generic "Platform-specific helper functions"
> term as suggested by David Vernet, rather than the kernel specific "kfuncs".
>
> ---
> V1 -> V2: addressed comments from David Vernet
>
> Signed-off-by: Dave Thaler <dthaler@xxxxxxxxxxxxx>
> ---
> Documentation/bpf/instruction-set.rst | 63 +++++++++++++++++----------
> Documentation/bpf/linux-notes.rst | 4 ++
> 2 files changed, 44 insertions(+), 23 deletions(-)
>
> diff --git a/Documentation/bpf/instruction-set.rst b/Documentation/bpf/instruction-set.rst
> index 5e43e14abe8..dc348544542 100644
> --- a/Documentation/bpf/instruction-set.rst
> +++ b/Documentation/bpf/instruction-set.rst
> @@ -242,35 +242,52 @@ Jump instructions
> otherwise identical operations.
> The 'code' field encodes the operation as below:
>
> -======== ===== ========================= ============
> -code value description notes
> -======== ===== ========================= ============
> -BPF_JA 0x00 PC += off BPF_JMP only
> -BPF_JEQ 0x10 PC += off if dst == src
> -BPF_JGT 0x20 PC += off if dst > src unsigned
> -BPF_JGE 0x30 PC += off if dst >= src unsigned
> -BPF_JSET 0x40 PC += off if dst & src
> -BPF_JNE 0x50 PC += off if dst != src
> -BPF_JSGT 0x60 PC += off if dst > src signed
> -BPF_JSGE 0x70 PC += off if dst >= src signed
> -BPF_CALL 0x80 function call see `Helper functions`_
> -BPF_EXIT 0x90 function / program return BPF_JMP only
> -BPF_JLT 0xa0 PC += off if dst < src unsigned
> -BPF_JLE 0xb0 PC += off if dst <= src unsigned
> -BPF_JSLT 0xc0 PC += off if dst < src signed
> -BPF_JSLE 0xd0 PC += off if dst <= src signed
> -======== ===== ========================= ============
> +======== ===== === ========================== =========================================
> +code value src description notes
> +======== ===== === ========================== =========================================
> +BPF_JA 0x0 0x0 PC += offset BPF_JMP only
> +BPF_JEQ 0x1 any PC += offset if dst == src
> +BPF_JGT 0x2 any PC += offset if dst > src unsigned
> +BPF_JGE 0x3 any PC += offset if dst >= src unsigned
> +BPF_JSET 0x4 any PC += offset if dst & src
> +BPF_JNE 0x5 any PC += offset if dst != src
> +BPF_JSGT 0x6 any PC += offset if dst > src signed
> +BPF_JSGE 0x7 any PC += offset if dst >= src signed
> +BPF_CALL 0x8 0x0 call helper function imm see `Platform-agnostic helper functions`_
> +BPF_CALL 0x8 0x1 call PC += offset see `BPF-local functions`_
> +BPF_CALL 0x8 0x2 call runtime function imm see `Platform-specific helper functions`_
> +BPF_EXIT 0x9 0x0 return BPF_JMP only
> +BPF_JLT 0xa any PC += offset if dst < src unsigned
> +BPF_JLE 0xb any PC += offset if dst <= src unsigned
> +BPF_JSLT 0xc any PC += offset if dst < src signed
> +BPF_JSLE 0xd any PC += offset if dst <= src signed
> +======== ===== === ========================== =========================================
>
> The eBPF program needs to store the return value into register R0 before doing a
> BPF_EXIT.
>
> -Helper functions
> -~~~~~~~~~~~~~~~~
> +Platform-agnostic helper functions
> +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>
> -Helper functions are a concept whereby BPF programs can call into a
> -set of function calls exposed by the runtime. Each helper
> +Platform-agnostic helper functions are a concept whereby BPF programs can call
> +into a set of function calls exposed by the runtime. Each helper
> function is identified by an integer used in a ``BPF_CALL`` instruction.
> -The available helper functions may differ for each program type.
> +The available platform-agnostic helper functions may differ for each program
> +type, but integer values are unique across all program types.
> +
> +Platform-specific helper functions
> +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> +Platform-specific helper functions are helper functions that are unique to
> +a particular platform. They use a separate integer numbering space from
> +platform-agnostic helper functions, but otherwise the same considerations
How does the separate integer numbering space work in Linux? Here I guess
we have platform agnostic and Linux specific helpers all mingled together
correct?
> +apply. Platforms are not required to implement any platform-specific
> +functions.
> +
> +BPF-local functions
> +~~~~~~~~~~~~~~
> +BPF-local functions are functions exposed by the same BPF program as the caller,
> +and are referenced by offset from the call instruction, similar to ``BPF_JA``.
> +A ``BPF_EXIT`` within the BPF-local function will return to the caller.
>
> Load and store instructions
> ===========================
> diff --git a/Documentation/bpf/linux-notes.rst b/Documentation/bpf/linux-notes.rst
> index f43b9c797bc..bdc41293e8a 100644
> --- a/Documentation/bpf/linux-notes.rst
> +++ b/Documentation/bpf/linux-notes.rst
> @@ -20,6 +20,10 @@ integer would be read from a specified register, is not currently supported
> by the verifier. Any programs with this instruction will fail to load
> until such support is added.
>
> +For historical reasons, Linux has a number of Linux-specific helper functions
> +that are encoded as platform-agnostic helper functions rather than
> + platform-specific helper functions ("kfuncs").
Is this the comment to address above integer numbering space on Linux
being inconsistent with above docs?
> +
> Legacy BPF Packet access instructions
> =====================================
>
> --
> 2.33.4
>
