UbiquitousOS
/
OpenCloudOS-Kernel
mirror of https://gitee.com/OpenCloudOS/OpenCloudOS-Kernel.git
11
0
Fork 0
Code Issues Projects Releases Wiki Activity
OpenCloudOS-Kernel/Documentation/bpf/instruction-set.rst

280 lines
8.9 KiB
ReStructuredText
Raw Normal View History

bpf, docs: Split general purpose eBPF documentation out of filter.rst filter.rst starts out documenting the classic BPF and then spills into introducing and documentating eBPF. Move the eBPF documentation into rwo new files under Documentation/bpf/ for the instruction set and the verifier and link to the BPF documentation from filter.rst. Signed-off-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Acked-by: Song Liu <songliubraving@fb.com> Link: https://lore.kernel.org/bpf/20211119163215.971383-6-hch@lst.de
2021-11-20 00:32:15 +08:00
====================
eBPF Instruction Set
====================
bpf, docs: Split the comparism to classic BPF from instruction-set.rst Split the introductory that explain eBPF vs classic BPF and how it maps to hardware from the instruction set specification into a standalone document. This duplicates a little bit of information but gives us a useful reference for the eBPF instrution set that is not encumbered by classic BPF. Signed-off-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Link: https://lore.kernel.org/bpf/20211223101906.977624-3-hch@lst.de
2021-12-23 18:19:04 +08:00
Registers and calling convention
================================
eBPF has 10 general purpose registers and a read-only frame pointer register,
all of which are 64-bits wide.
The eBPF calling convention is defined as:
* R0: return value from function calls, and exit value for eBPF programs
* R1 - R5: arguments for function calls
* R6 - R9: callee saved registers that function calls will preserve
* R10: read-only frame pointer to access stack
R0 - R5 are scratch registers and eBPF programs needs to spill/fill them if
necessary across calls.
bpf, docs: Split general purpose eBPF documentation out of filter.rst filter.rst starts out documenting the classic BPF and then spills into introducing and documentating eBPF. Move the eBPF documentation into rwo new files under Documentation/bpf/ for the instruction set and the verifier and link to the BPF documentation from filter.rst. Signed-off-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Acked-by: Song Liu <songliubraving@fb.com> Link: https://lore.kernel.org/bpf/20211119163215.971383-6-hch@lst.de
2021-11-20 00:32:15 +08:00
bpf, docs: Add a setion to explain the basic instruction encoding The eBPF instruction set document does not currently document the basic instruction encoding. Add a section to do that. Signed-off-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Link: https://lore.kernel.org/bpf/20220103183556.41040-2-hch@lst.de
2022-01-04 02:35:51 +08:00
Instruction encoding
====================
eBPF uses 64-bit instructions with the following encoding:
============= ======= =============== ==================== ============
32 bits (MSB) 16 bits 4 bits 4 bits 8 bits (LSB)
============= ======= =============== ==================== ============
immediate offset source register destination register opcode
============= ======= =============== ==================== ============
Note that most instructions do not use all of the fields.
Unused fields shall be cleared to zero.
bpf, docs: Generate nicer tables for instruction encodings Use RST tables that are nicely readable both in plain ascii as well as in html to render the instruction encodings, and add a few subheadings to better structure the text. Signed-off-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Link: https://lore.kernel.org/bpf/20211223101906.977624-4-hch@lst.de
2021-12-23 18:19:05 +08:00
Instruction classes
bpf, docs: Add a setion to explain the basic instruction encoding The eBPF instruction set document does not currently document the basic instruction encoding. Add a section to do that. Signed-off-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Link: https://lore.kernel.org/bpf/20220103183556.41040-2-hch@lst.de
2022-01-04 02:35:51 +08:00
-------------------
bpf, docs: Split general purpose eBPF documentation out of filter.rst filter.rst starts out documenting the classic BPF and then spills into introducing and documentating eBPF. Move the eBPF documentation into rwo new files under Documentation/bpf/ for the instruction set and the verifier and link to the BPF documentation from filter.rst. Signed-off-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Acked-by: Song Liu <songliubraving@fb.com> Link: https://lore.kernel.org/bpf/20211119163215.971383-6-hch@lst.de
2021-11-20 00:32:15 +08:00
bpf, docs: Generate nicer tables for instruction encodings Use RST tables that are nicely readable both in plain ascii as well as in html to render the instruction encodings, and add a few subheadings to better structure the text. Signed-off-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Link: https://lore.kernel.org/bpf/20211223101906.977624-4-hch@lst.de
2021-12-23 18:19:05 +08:00
The three LSB bits of the 'opcode' field store the instruction class:
bpf, docs: Split general purpose eBPF documentation out of filter.rst filter.rst starts out documenting the classic BPF and then spills into introducing and documentating eBPF. Move the eBPF documentation into rwo new files under Documentation/bpf/ for the instruction set and the verifier and link to the BPF documentation from filter.rst. Signed-off-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Acked-by: Song Liu <songliubraving@fb.com> Link: https://lore.kernel.org/bpf/20211119163215.971383-6-hch@lst.de
2021-11-20 00:32:15 +08:00
bpf, docs: Document the opcode classes Add a description for each opcode class. Signed-off-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Link: https://lore.kernel.org/bpf/20220103183556.41040-4-hch@lst.de
2022-01-04 02:35:53 +08:00
========= ===== ===============================
class value description
========= ===== ===============================
BPF_LD 0x00 non-standard load operations
BPF_LDX 0x01 load into register operations
BPF_ST 0x02 store from immediate operations
BPF_STX 0x03 store from register operations
BPF_ALU 0x04 32-bit arithmetic operations
BPF_JMP 0x05 64-bit jump operations
BPF_JMP32 0x06 32-bit jump operations
BPF_ALU64 0x07 64-bit arithmetic operations
========= ===== ===============================
bpf, docs: Split general purpose eBPF documentation out of filter.rst filter.rst starts out documenting the classic BPF and then spills into introducing and documentating eBPF. Move the eBPF documentation into rwo new files under Documentation/bpf/ for the instruction set and the verifier and link to the BPF documentation from filter.rst. Signed-off-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Acked-by: Song Liu <songliubraving@fb.com> Link: https://lore.kernel.org/bpf/20211119163215.971383-6-hch@lst.de
2021-11-20 00:32:15 +08:00
bpf, docs: Generate nicer tables for instruction encodings Use RST tables that are nicely readable both in plain ascii as well as in html to render the instruction encodings, and add a few subheadings to better structure the text. Signed-off-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Link: https://lore.kernel.org/bpf/20211223101906.977624-4-hch@lst.de
2021-12-23 18:19:05 +08:00
Arithmetic and jump instructions
================================
For arithmetic and jump instructions (BPF_ALU, BPF_ALU64, BPF_JMP and
BPF_JMP32), the 8-bit 'opcode' field is divided into three parts:
bpf, docs: Split general purpose eBPF documentation out of filter.rst filter.rst starts out documenting the classic BPF and then spills into introducing and documentating eBPF. Move the eBPF documentation into rwo new files under Documentation/bpf/ for the instruction set and the verifier and link to the BPF documentation from filter.rst. Signed-off-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Acked-by: Song Liu <songliubraving@fb.com> Link: https://lore.kernel.org/bpf/20211119163215.971383-6-hch@lst.de
2021-11-20 00:32:15 +08:00
bpf, docs: Generate nicer tables for instruction encodings Use RST tables that are nicely readable both in plain ascii as well as in html to render the instruction encodings, and add a few subheadings to better structure the text. Signed-off-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Link: https://lore.kernel.org/bpf/20211223101906.977624-4-hch@lst.de
2021-12-23 18:19:05 +08:00
============== ====== =================
4 bits (MSB) 1 bit 3 bits (LSB)
============== ====== =================
operation code source instruction class
============== ====== =================
bpf, docs: Split general purpose eBPF documentation out of filter.rst filter.rst starts out documenting the classic BPF and then spills into introducing and documentating eBPF. Move the eBPF documentation into rwo new files under Documentation/bpf/ for the instruction set and the verifier and link to the BPF documentation from filter.rst. Signed-off-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Acked-by: Song Liu <songliubraving@fb.com> Link: https://lore.kernel.org/bpf/20211119163215.971383-6-hch@lst.de
2021-11-20 00:32:15 +08:00
bpf, docs: Generate nicer tables for instruction encodings Use RST tables that are nicely readable both in plain ascii as well as in html to render the instruction encodings, and add a few subheadings to better structure the text. Signed-off-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Link: https://lore.kernel.org/bpf/20211223101906.977624-4-hch@lst.de
2021-12-23 18:19:05 +08:00
The 4th bit encodes the source operand:
bpf, docs: Split general purpose eBPF documentation out of filter.rst filter.rst starts out documenting the classic BPF and then spills into introducing and documentating eBPF. Move the eBPF documentation into rwo new files under Documentation/bpf/ for the instruction set and the verifier and link to the BPF documentation from filter.rst. Signed-off-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Acked-by: Song Liu <songliubraving@fb.com> Link: https://lore.kernel.org/bpf/20211119163215.971383-6-hch@lst.de
2021-11-20 00:32:15 +08:00
bpf, docs: Generate nicer tables for instruction encodings Use RST tables that are nicely readable both in plain ascii as well as in html to render the instruction encodings, and add a few subheadings to better structure the text. Signed-off-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Link: https://lore.kernel.org/bpf/20211223101906.977624-4-hch@lst.de
2021-12-23 18:19:05 +08:00
====== ===== ========================================
source value description
====== ===== ========================================
BPF_K 0x00 use 32-bit immediate as source operand
BPF_X 0x08 use 'src_reg' register as source operand
====== ===== ========================================
bpf, docs: Split general purpose eBPF documentation out of filter.rst filter.rst starts out documenting the classic BPF and then spills into introducing and documentating eBPF. Move the eBPF documentation into rwo new files under Documentation/bpf/ for the instruction set and the verifier and link to the BPF documentation from filter.rst. Signed-off-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Acked-by: Song Liu <songliubraving@fb.com> Link: https://lore.kernel.org/bpf/20211119163215.971383-6-hch@lst.de
2021-11-20 00:32:15 +08:00
bpf, docs: Generate nicer tables for instruction encodings Use RST tables that are nicely readable both in plain ascii as well as in html to render the instruction encodings, and add a few subheadings to better structure the text. Signed-off-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Link: https://lore.kernel.org/bpf/20211223101906.977624-4-hch@lst.de
2021-12-23 18:19:05 +08:00
The four MSB bits store the operation code.
bpf, docs: Split general purpose eBPF documentation out of filter.rst filter.rst starts out documenting the classic BPF and then spills into introducing and documentating eBPF. Move the eBPF documentation into rwo new files under Documentation/bpf/ for the instruction set and the verifier and link to the BPF documentation from filter.rst. Signed-off-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Acked-by: Song Liu <songliubraving@fb.com> Link: https://lore.kernel.org/bpf/20211119163215.971383-6-hch@lst.de
2021-11-20 00:32:15 +08:00
bpf, docs: Add subsections for ALU and JMP instructions Add a little more stucture to the ALU/JMP documentation with sections and improve the example text. Signed-off-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Link: https://lore.kernel.org/bpf/20220103183556.41040-3-hch@lst.de
2022-01-04 02:35:52 +08:00
Arithmetic instructions
-----------------------
BPF_ALU uses 32-bit wide operands while BPF_ALU64 uses 64-bit wide operands for
otherwise identical operations.
The code field encodes the operation as below:
bpf, docs: Generate nicer tables for instruction encodings Use RST tables that are nicely readable both in plain ascii as well as in html to render the instruction encodings, and add a few subheadings to better structure the text. Signed-off-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Link: https://lore.kernel.org/bpf/20211223101906.977624-4-hch@lst.de
2021-12-23 18:19:05 +08:00
======== ===== =========================
code value description
======== ===== =========================
bpf, docs: Split general purpose eBPF documentation out of filter.rst filter.rst starts out documenting the classic BPF and then spills into introducing and documentating eBPF. Move the eBPF documentation into rwo new files under Documentation/bpf/ for the instruction set and the verifier and link to the BPF documentation from filter.rst. Signed-off-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Acked-by: Song Liu <songliubraving@fb.com> Link: https://lore.kernel.org/bpf/20211119163215.971383-6-hch@lst.de
2021-11-20 00:32:15 +08:00
BPF_ADD 0x00
BPF_SUB 0x10
BPF_MUL 0x20
BPF_DIV 0x30
BPF_OR 0x40
BPF_AND 0x50
BPF_LSH 0x60
BPF_RSH 0x70
BPF_NEG 0x80
BPF_MOD 0x90
BPF_XOR 0xa0
bpf, docs: Generate nicer tables for instruction encodings Use RST tables that are nicely readable both in plain ascii as well as in html to render the instruction encodings, and add a few subheadings to better structure the text. Signed-off-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Link: https://lore.kernel.org/bpf/20211223101906.977624-4-hch@lst.de
2021-12-23 18:19:05 +08:00
BPF_MOV 0xb0 mov reg to reg
BPF_ARSH 0xc0 sign extending shift right
BPF_END 0xd0 endianness conversion
======== ===== =========================
bpf, docs: Split general purpose eBPF documentation out of filter.rst filter.rst starts out documenting the classic BPF and then spills into introducing and documentating eBPF. Move the eBPF documentation into rwo new files under Documentation/bpf/ for the instruction set and the verifier and link to the BPF documentation from filter.rst. Signed-off-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Acked-by: Song Liu <songliubraving@fb.com> Link: https://lore.kernel.org/bpf/20211119163215.971383-6-hch@lst.de
2021-11-20 00:32:15 +08:00
bpf, docs: Add subsections for ALU and JMP instructions Add a little more stucture to the ALU/JMP documentation with sections and improve the example text. Signed-off-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Link: https://lore.kernel.org/bpf/20220103183556.41040-3-hch@lst.de
2022-01-04 02:35:52 +08:00
BPF_ADD | BPF_X | BPF_ALU means::
dst_reg = (u32) dst_reg + (u32) src_reg;
BPF_ADD | BPF_X | BPF_ALU64 means::
dst_reg = dst_reg + src_reg
BPF_XOR | BPF_K | BPF_ALU means::
src_reg = (u32) src_reg ^ (u32) imm32
BPF_XOR | BPF_K | BPF_ALU64 means::
src_reg = src_reg ^ imm32
Jump instructions
-----------------
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:
bpf, docs: Split general purpose eBPF documentation out of filter.rst filter.rst starts out documenting the classic BPF and then spills into introducing and documentating eBPF. Move the eBPF documentation into rwo new files under Documentation/bpf/ for the instruction set and the verifier and link to the BPF documentation from filter.rst. Signed-off-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Acked-by: Song Liu <songliubraving@fb.com> Link: https://lore.kernel.org/bpf/20211119163215.971383-6-hch@lst.de
2021-11-20 00:32:15 +08:00
bpf, docs: Generate nicer tables for instruction encodings Use RST tables that are nicely readable both in plain ascii as well as in html to render the instruction encodings, and add a few subheadings to better structure the text. Signed-off-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Link: https://lore.kernel.org/bpf/20211223101906.977624-4-hch@lst.de
2021-12-23 18:19:05 +08:00
======== ===== =========================
code value description
======== ===== =========================
BPF_JA 0x00 BPF_JMP only
bpf, docs: Split general purpose eBPF documentation out of filter.rst filter.rst starts out documenting the classic BPF and then spills into introducing and documentating eBPF. Move the eBPF documentation into rwo new files under Documentation/bpf/ for the instruction set and the verifier and link to the BPF documentation from filter.rst. Signed-off-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Acked-by: Song Liu <songliubraving@fb.com> Link: https://lore.kernel.org/bpf/20211119163215.971383-6-hch@lst.de
2021-11-20 00:32:15 +08:00
BPF_JEQ 0x10
BPF_JGT 0x20
BPF_JGE 0x30
BPF_JSET 0x40
bpf, docs: Generate nicer tables for instruction encodings Use RST tables that are nicely readable both in plain ascii as well as in html to render the instruction encodings, and add a few subheadings to better structure the text. Signed-off-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Link: https://lore.kernel.org/bpf/20211223101906.977624-4-hch@lst.de
2021-12-23 18:19:05 +08:00
BPF_JNE 0x50 jump '!='
BPF_JSGT 0x60 signed '>'
BPF_JSGE 0x70 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, docs: Split the comparism to classic BPF from instruction-set.rst Split the introductory that explain eBPF vs classic BPF and how it maps to hardware from the instruction set specification into a standalone document. This duplicates a little bit of information but gives us a useful reference for the eBPF instrution set that is not encumbered by classic BPF. Signed-off-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Link: https://lore.kernel.org/bpf/20211223101906.977624-3-hch@lst.de
2021-12-23 18:19:04 +08:00
bpf, docs: Add subsections for ALU and JMP instructions Add a little more stucture to the ALU/JMP documentation with sections and improve the example text. Signed-off-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Link: https://lore.kernel.org/bpf/20220103183556.41040-3-hch@lst.de
2022-01-04 02:35:52 +08:00
The eBPF program needs to store the return value into register R0 before doing a
BPF_EXIT.
bpf, docs: Split general purpose eBPF documentation out of filter.rst filter.rst starts out documenting the classic BPF and then spills into introducing and documentating eBPF. Move the eBPF documentation into rwo new files under Documentation/bpf/ for the instruction set and the verifier and link to the BPF documentation from filter.rst. Signed-off-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Acked-by: Song Liu <songliubraving@fb.com> Link: https://lore.kernel.org/bpf/20211119163215.971383-6-hch@lst.de
2021-11-20 00:32:15 +08:00
bpf, docs: Generate nicer tables for instruction encodings Use RST tables that are nicely readable both in plain ascii as well as in html to render the instruction encodings, and add a few subheadings to better structure the text. Signed-off-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Link: https://lore.kernel.org/bpf/20211223101906.977624-4-hch@lst.de
2021-12-23 18:19:05 +08:00
Load and store instructions
===========================
For load and store instructions (BPF_LD, BPF_LDX, BPF_ST and BPF_STX), the
8-bit 'opcode' field is divided as:
============ ====== =================
3 bits (MSB) 2 bits 3 bits (LSB)
============ ====== =================
mode size instruction class
============ ====== =================
The size modifier is one of:
bpf, docs: Split general purpose eBPF documentation out of filter.rst filter.rst starts out documenting the classic BPF and then spills into introducing and documentating eBPF. Move the eBPF documentation into rwo new files under Documentation/bpf/ for the instruction set and the verifier and link to the BPF documentation from filter.rst. Signed-off-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Acked-by: Song Liu <songliubraving@fb.com> Link: https://lore.kernel.org/bpf/20211119163215.971383-6-hch@lst.de
2021-11-20 00:32:15 +08:00
bpf, docs: Generate nicer tables for instruction encodings Use RST tables that are nicely readable both in plain ascii as well as in html to render the instruction encodings, and add a few subheadings to better structure the text. Signed-off-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Link: https://lore.kernel.org/bpf/20211223101906.977624-4-hch@lst.de
2021-12-23 18:19:05 +08:00
============= ===== =====================
size modifier value description
============= ===== =====================
BPF_W 0x00 word (4 bytes)
BPF_H 0x08 half word (2 bytes)
BPF_B 0x10 byte
BPF_DW 0x18 double word (8 bytes)
============= ===== =====================
bpf, docs: Split general purpose eBPF documentation out of filter.rst filter.rst starts out documenting the classic BPF and then spills into introducing and documentating eBPF. Move the eBPF documentation into rwo new files under Documentation/bpf/ for the instruction set and the verifier and link to the BPF documentation from filter.rst. Signed-off-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Acked-by: Song Liu <songliubraving@fb.com> Link: https://lore.kernel.org/bpf/20211119163215.971383-6-hch@lst.de
2021-11-20 00:32:15 +08:00
bpf, docs: Generate nicer tables for instruction encodings Use RST tables that are nicely readable both in plain ascii as well as in html to render the instruction encodings, and add a few subheadings to better structure the text. Signed-off-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Link: https://lore.kernel.org/bpf/20211223101906.977624-4-hch@lst.de
2021-12-23 18:19:05 +08:00
The mode modifier is one of:
bpf, docs: Split general purpose eBPF documentation out of filter.rst filter.rst starts out documenting the classic BPF and then spills into introducing and documentating eBPF. Move the eBPF documentation into rwo new files under Documentation/bpf/ for the instruction set and the verifier and link to the BPF documentation from filter.rst. Signed-off-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Acked-by: Song Liu <songliubraving@fb.com> Link: https://lore.kernel.org/bpf/20211119163215.971383-6-hch@lst.de
2021-11-20 00:32:15 +08:00
bpf, docs: Generate nicer tables for instruction encodings Use RST tables that are nicely readable both in plain ascii as well as in html to render the instruction encodings, and add a few subheadings to better structure the text. Signed-off-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Link: https://lore.kernel.org/bpf/20211223101906.977624-4-hch@lst.de
2021-12-23 18:19:05 +08:00
============= ===== =====================
mode modifier value description
============= ===== =====================
BPF_IMM 0x00 used for 64-bit mov
BPF_ABS 0x20
BPF_IND 0x40
BPF_MEM 0x60
BPF_ATOMIC 0xc0 atomic operations
============= ===== =====================
bpf, docs: Split general purpose eBPF documentation out of filter.rst filter.rst starts out documenting the classic BPF and then spills into introducing and documentating eBPF. Move the eBPF documentation into rwo new files under Documentation/bpf/ for the instruction set and the verifier and link to the BPF documentation from filter.rst. Signed-off-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Acked-by: Song Liu <songliubraving@fb.com> Link: https://lore.kernel.org/bpf/20211119163215.971383-6-hch@lst.de
2021-11-20 00:32:15 +08:00
bpf, docs: Generate nicer tables for instruction encodings Use RST tables that are nicely readable both in plain ascii as well as in html to render the instruction encodings, and add a few subheadings to better structure the text. Signed-off-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Link: https://lore.kernel.org/bpf/20211223101906.977624-4-hch@lst.de
2021-12-23 18:19:05 +08:00
BPF_MEM | <size> | BPF_STX means::
bpf, docs: Split general purpose eBPF documentation out of filter.rst filter.rst starts out documenting the classic BPF and then spills into introducing and documentating eBPF. Move the eBPF documentation into rwo new files under Documentation/bpf/ for the instruction set and the verifier and link to the BPF documentation from filter.rst. Signed-off-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Acked-by: Song Liu <songliubraving@fb.com> Link: https://lore.kernel.org/bpf/20211119163215.971383-6-hch@lst.de
2021-11-20 00:32:15 +08:00
bpf, docs: Generate nicer tables for instruction encodings Use RST tables that are nicely readable both in plain ascii as well as in html to render the instruction encodings, and add a few subheadings to better structure the text. Signed-off-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Link: https://lore.kernel.org/bpf/20211223101906.977624-4-hch@lst.de
2021-12-23 18:19:05 +08:00
*(size *) (dst_reg + off) = src_reg
bpf, docs: Split general purpose eBPF documentation out of filter.rst filter.rst starts out documenting the classic BPF and then spills into introducing and documentating eBPF. Move the eBPF documentation into rwo new files under Documentation/bpf/ for the instruction set and the verifier and link to the BPF documentation from filter.rst. Signed-off-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Acked-by: Song Liu <songliubraving@fb.com> Link: https://lore.kernel.org/bpf/20211119163215.971383-6-hch@lst.de
2021-11-20 00:32:15 +08:00
bpf, docs: Generate nicer tables for instruction encodings Use RST tables that are nicely readable both in plain ascii as well as in html to render the instruction encodings, and add a few subheadings to better structure the text. Signed-off-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Link: https://lore.kernel.org/bpf/20211223101906.977624-4-hch@lst.de
2021-12-23 18:19:05 +08:00
BPF_MEM | <size> | BPF_ST means::
bpf, docs: Split general purpose eBPF documentation out of filter.rst filter.rst starts out documenting the classic BPF and then spills into introducing and documentating eBPF. Move the eBPF documentation into rwo new files under Documentation/bpf/ for the instruction set and the verifier and link to the BPF documentation from filter.rst. Signed-off-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Acked-by: Song Liu <songliubraving@fb.com> Link: https://lore.kernel.org/bpf/20211119163215.971383-6-hch@lst.de
2021-11-20 00:32:15 +08:00
bpf, docs: Generate nicer tables for instruction encodings Use RST tables that are nicely readable both in plain ascii as well as in html to render the instruction encodings, and add a few subheadings to better structure the text. Signed-off-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Link: https://lore.kernel.org/bpf/20211223101906.977624-4-hch@lst.de
2021-12-23 18:19:05 +08:00
*(size *) (dst_reg + off) = imm32
BPF_MEM | <size> | BPF_LDX means::
dst_reg = *(size *) (src_reg + off)
Where size is one of: BPF_B or BPF_H or BPF_W or BPF_DW.
Atomic operations
-----------------
bpf, docs: Split general purpose eBPF documentation out of filter.rst filter.rst starts out documenting the classic BPF and then spills into introducing and documentating eBPF. Move the eBPF documentation into rwo new files under Documentation/bpf/ for the instruction set and the verifier and link to the BPF documentation from filter.rst. Signed-off-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Acked-by: Song Liu <songliubraving@fb.com> Link: https://lore.kernel.org/bpf/20211119163215.971383-6-hch@lst.de
2021-11-20 00:32:15 +08:00
bpf, docs: Generate nicer tables for instruction encodings Use RST tables that are nicely readable both in plain ascii as well as in html to render the instruction encodings, and add a few subheadings to better structure the text. Signed-off-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Link: https://lore.kernel.org/bpf/20211223101906.977624-4-hch@lst.de
2021-12-23 18:19:05 +08:00
eBPF includes atomic operations, which use the immediate field for extra
bpf, docs: Split general purpose eBPF documentation out of filter.rst filter.rst starts out documenting the classic BPF and then spills into introducing and documentating eBPF. Move the eBPF documentation into rwo new files under Documentation/bpf/ for the instruction set and the verifier and link to the BPF documentation from filter.rst. Signed-off-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Acked-by: Song Liu <songliubraving@fb.com> Link: https://lore.kernel.org/bpf/20211119163215.971383-6-hch@lst.de
2021-11-20 00:32:15 +08:00
encoding::
.imm = BPF_ADD, .code = BPF_ATOMIC | BPF_W | BPF_STX: lock xadd *(u32 *)(dst_reg + off16) += src_reg
.imm = BPF_ADD, .code = BPF_ATOMIC | BPF_DW | BPF_STX: lock xadd *(u64 *)(dst_reg + off16) += src_reg
The basic atomic operations supported are::
BPF_ADD
BPF_AND
BPF_OR
BPF_XOR
Each having equivalent semantics with the ``BPF_ADD`` example, that is: the
memory location addresed by ``dst_reg + off`` is atomically modified, with
``src_reg`` as the other operand. If the ``BPF_FETCH`` flag is set in the
immediate, then these operations also overwrite ``src_reg`` with the
value that was in memory before it was modified.
The more special operations are::
BPF_XCHG
This atomically exchanges ``src_reg`` with the value addressed by ``dst_reg +
off``. ::
BPF_CMPXCHG
This atomically compares the value addressed by ``dst_reg + off`` with
``R0``. If they match it is replaced with ``src_reg``. In either case, the
value that was there before is zero-extended and loaded back to ``R0``.
Note that 1 and 2 byte atomic operations are not supported.
Clang can generate atomic instructions by default when ``-mcpu=v3`` is
enabled. If a lower version for ``-mcpu`` is set, the only atomic instruction
Clang can generate is ``BPF_ADD`` *without* ``BPF_FETCH``. If you need to enable
the atomics features, while keeping a lower ``-mcpu`` version, you can use
``-Xclang -target-feature -Xclang +alu32``.
You may encounter ``BPF_XADD`` - this is a legacy name for ``BPF_ATOMIC``,
referring to the exclusive-add operation encoded when the immediate field is
zero.
bpf, docs: Generate nicer tables for instruction encodings Use RST tables that are nicely readable both in plain ascii as well as in html to render the instruction encodings, and add a few subheadings to better structure the text. Signed-off-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Link: https://lore.kernel.org/bpf/20211223101906.977624-4-hch@lst.de
2021-12-23 18:19:05 +08:00
16-byte instructions
--------------------
bpf, docs: Split general purpose eBPF documentation out of filter.rst filter.rst starts out documenting the classic BPF and then spills into introducing and documentating eBPF. Move the eBPF documentation into rwo new files under Documentation/bpf/ for the instruction set and the verifier and link to the BPF documentation from filter.rst. Signed-off-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Acked-by: Song Liu <songliubraving@fb.com> Link: https://lore.kernel.org/bpf/20211119163215.971383-6-hch@lst.de
2021-11-20 00:32:15 +08:00
eBPF has one 16-byte instruction: ``BPF_LD | BPF_DW | BPF_IMM`` which consists
of two consecutive ``struct bpf_insn`` 8-byte blocks and interpreted as single
instruction that loads 64-bit immediate value into a dst_reg.
bpf, docs: Move the packet access instructions last in instruction-set.rst The packet access instructions are a convoluted leftover from classic BPF. Move them last past the much more important atomic operations, and improve the rendering of the code example. Signed-off-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Link: https://lore.kernel.org/bpf/20211223101906.977624-5-hch@lst.de
2021-12-23 18:19:06 +08:00
Packet access instructions
--------------------------
eBPF has two non-generic instructions: (BPF_ABS | <size> | BPF_LD) and
(BPF_IND | <size> | BPF_LD) which are used to access packet data.
They had to be carried over from classic BPF to have strong performance of
socket filters running in eBPF interpreter. These instructions can only
be used when interpreter context is a pointer to ``struct sk_buff`` and
have seven implicit operands. Register R6 is an implicit input that must
contain pointer to sk_buff. Register R0 is an implicit output which contains
the data fetched from the packet. Registers R1-R5 are scratch registers
and must not be used to store the data across BPF_ABS | BPF_LD or
BPF_IND | BPF_LD instructions.
These instructions have implicit program exit condition as well. When
eBPF program is trying to access the data beyond the packet boundary,
the interpreter will abort the execution of the program. JIT compilers
therefore must preserve this property. src_reg and imm32 fields are
explicit inputs to these instructions.
For example, BPF_IND | BPF_W | BPF_LD means::
R0 = ntohl(*(u32 *) (((struct sk_buff *) R6)->data + src_reg + imm32))
and R1 - R5 are clobbered.