[PATCH bpf-next] bpf, docs: Add extended call instructions

[Dave Thaler <dthaler1968@googlemail.com>]

From: Dave Thaler <dthaler@microsoft.com>

Add extended call instructions.  Since BPF can be used in userland
or SmartNICs, this uses the more generic "runtime functions"
rather than the kernel specific "kfuncs" as a term.

Signed-off-by: Dave Thaler <dthaler@microsoft.com>
---
 Documentation/bpf/instruction-set.rst | 50 +++++++++++++++++----------
 1 file changed, 32 insertions(+), 18 deletions(-)

diff --git a/Documentation/bpf/instruction-set.rst b/Documentation/bpf/instruction-set.rst
index 5e43e14abe8..bc2319a7707 100644
--- a/Documentation/bpf/instruction-set.rst
+++ b/Documentation/bpf/instruction-set.rst
@@ -242,24 +242,26 @@ 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 `Helper functions`_
+BPF_CALL  0x8    0x1  call PC += offset           see `eBPF functions`_
+BPF_CALL  0x8    0x2  call runtime function imm   see `Runtime 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.
@@ -272,6 +274,18 @@ 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.
 
+Runtime functions
+~~~~~~~~~~~~~~~~~
+Runtime functions are like helper functions except that they are not specific
+to eBPF programs.  They use a different numbering space from helper functions,
+but otherwise the same considerations apply.
+
+eBPF functions
+~~~~~~~~~~~~~~
+eBPF functions are functions exposed by the same eBPF program as the caller,
+and are referenced by offset from the call instruction, similar to ``BPF_JA``.
+A ``BPF_EXIT`` within the eBPF function will return to the caller.
+
 Load and store instructions
 ===========================
 
-- 
2.33.4