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bpf, docs: Fully document the JMP opcodes 

Add pseudo-code to document all the different BPF_JMP / BPF_JMP64
opcodes.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20220103183556.41040-6-hch@lst.de
This commit is contained in:
Christoph Hellwig 2022-01-03 19:35:55 +01:00 committed by Alexei Starovoitov
parent 03c517ee9e
commit 9e533e22b5
1 changed files with 17 additions and 17 deletions
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34
Documentation/bpf/instruction-set.rst
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@ -125,24 +125,24 @@ BPF_JMP32 uses 32-bit wide operands while BPF_JMP uses 64-bit wide operands for
otherwise identical operations.
The code field encodes the operation as below:
======== ===== =========================
code value description
======== ===== =========================
BPF_JA 0x00 BPF_JMP only
BPF_JEQ 0x10
BPF_JGT 0x20
BPF_JGE 0x30
BPF_JSET 0x40
BPF_JNE 0x50 jump '!='
BPF_JSGT 0x60 signed '>'
BPF_JSGE 0x70 signed '>='
======== ===== ========================= ============
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
BPF_EXIT 0x90 function return
BPF_JLT 0xa0 unsigned '<'
BPF_JLE 0xb0 unsigned '<='
BPF_JSLT 0xc0 signed '<'
BPF_JSLE 0xd0 signed '<='
======== ===== =========================
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
======== ===== ========================= ============
The eBPF program needs to store the return value into register R0 before doing a
BPF_EXIT.