Commit 9e533e22 authored by Christoph Hellwig's avatar Christoph Hellwig Committed by Alexei Starovoitov
Browse files

bpf, docs: Fully document the JMP opcodes 



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

Signed-off-by: default avatarChristoph Hellwig <hch@lst.de>
Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20220103183556.41040-6-hch@lst.de
parent 03c517ee

Documentation/bpf/instruction-set.rst

+17 −17
Original line number Diff line number Diff line
@@ -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.