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
+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").
+
Legacy BPF Packet access instructions
=====================================
--
2.33.4
