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bpf, docs: Add extended call instructions

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Add extended call instructions.  Uses the term "program-local" for
call by offset.  And there are instructions for calling helper functions
by "address" (the old way of using integer values), and for calling
helper functions by BTF ID (for kfuncs).

V1 -> V2: addressed comments from David Vernet

V2 -> V3: make descriptions in table consistent with updated names

V3 -> V4: addressed comments from Alexei

V4 -> V5: fixed alignment

Signed-off-by: Dave Thaler <dthaler@microsoft.com>
Acked-by: David Vernet <void@manifault.com>
Link: https://lore.kernel.org/r/20230326033117.1075-1-dthaler1968@googlemail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Dave Thaler 2023-03-26 03:31:17 +00:00 committed by Alexei Starovoitov
parent 8d2759608c
commit 8cfee11071
1 changed files with 37 additions and 22 deletions
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59
Documentation/bpf/instruction-set.rst
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@ -243,27 +243,29 @@ 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 by address see `Helper functions`_
BPF_CALL 0x8 0x1 call PC += offset see `Program-local functions`_
BPF_CALL 0x8 0x2 call helper function by BTF ID see `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.
``BPF_EXIT``.
Example:
@ -277,9 +279,22 @@ Helper functions
~~~~~~~~~~~~~~~~
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.
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
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
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
``BPF_JA``. A ``BPF_EXIT`` within the program-local function will return to
the caller.
Load and store instructions
===========================