From e48f0f4a9bfed8947e4d1123e8b6a15c18ee1708 Mon Sep 17 00:00:00 2001 From: Dave Thaler Date: Thu, 25 Jan 2024 20:00:50 -0800 Subject: bpf, docs: Clarify definitions of various instructions Clarify definitions of several instructions: * BPF_NEG does not support BPF_X * BPF_CALL does not support BPF_JMP32 or BPF_X * BPF_EXIT does not support BPF_X * BPF_JA does not support BPF_X (was implied but not explicitly stated) Also fix a typo in the wide instruction figure where the field is actually named "opcode" not "code". Signed-off-by: Dave Thaler Signed-off-by: Daniel Borkmann Acked-by: Yonghong Song Link: https://lore.kernel.org/bpf/20240126040050.8464-1-dthaler1968@gmail.com --- .../bpf/standardization/instruction-set.rst | 51 ++++++++++++---------- 1 file changed, 27 insertions(+), 24 deletions(-) diff --git a/Documentation/bpf/standardization/instruction-set.rst b/Documentation/bpf/standardization/instruction-set.rst index d17a96c6254f..af43227b6ee4 100644 --- a/Documentation/bpf/standardization/instruction-set.rst +++ b/Documentation/bpf/standardization/instruction-set.rst @@ -174,12 +174,12 @@ and imm containing the high 32 bits of the immediate value. This is depicted in the following figure:: basic_instruction - .-----------------------------. - | | - code:8 regs:8 offset:16 imm:32 unused:32 imm:32 - | | - '--------------' - pseudo instruction + .------------------------------. + | | + opcode:8 regs:8 offset:16 imm:32 unused:32 imm:32 + | | + '--------------' + pseudo instruction Thus the 64-bit immediate value is constructed as follows: @@ -320,6 +320,9 @@ bit operands, and zeroes the remaining upper 32 bits. operands into 64 bit operands. Unlike other arithmetic instructions, ``BPF_MOVSX`` is only defined for register source operands (``BPF_X``). +The ``BPF_NEG`` instruction is only defined when the source bit is clear +(``BPF_K``). + Shift operations use a mask of 0x3F (63) for 64-bit operations and 0x1F (31) for 32-bit operations. @@ -375,27 +378,27 @@ Jump instructions otherwise identical operations. The 'code' field encodes the operation as below: -======== ===== === =========================================== ========================================= -code value src description notes -======== ===== === =========================================== ========================================= -BPF_JA 0x0 0x0 PC += offset BPF_JMP class -BPF_JA 0x0 0x0 PC += imm BPF_JMP32 class +======== ===== === =============================== ============================================= +code value src description notes +======== ===== === =============================== ============================================= +BPF_JA 0x0 0x0 PC += offset BPF_JMP | BPF_K only +BPF_JA 0x0 0x0 PC += imm BPF_JMP32 | BPF_K 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_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 += imm 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 -======== ===== === =========================================== ========================================= +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 BPF_JMP | BPF_K only, see `Helper functions`_ +BPF_CALL 0x8 0x1 call PC += imm BPF_JMP | BPF_K only, see `Program-local functions`_ +BPF_CALL 0x8 0x2 call helper function by BTF ID BPF_JMP | BPF_K only, see `Helper functions`_ +BPF_EXIT 0x9 0x0 return BPF_JMP | BPF_K 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 BPF program needs to store the return value into register R0 before doing a ``BPF_EXIT``. -- cgit