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Diffstat (limited to 'Documentation/networking/filter.rst')
| -rw-r--r-- | Documentation/networking/filter.rst | 30 |
1 files changed, 19 insertions, 11 deletions
diff --git a/Documentation/networking/filter.rst b/Documentation/networking/filter.rst index debb59e374de..1583d59d806d 100644 --- a/Documentation/networking/filter.rst +++ b/Documentation/networking/filter.rst @@ -1006,13 +1006,13 @@ Size modifier is one of ... Mode modifier is one of:: - BPF_IMM 0x00 /* used for 32-bit mov in classic BPF and 64-bit in eBPF */ - BPF_ABS 0x20 - BPF_IND 0x40 - BPF_MEM 0x60 - BPF_LEN 0x80 /* classic BPF only, reserved in eBPF */ - BPF_MSH 0xa0 /* classic BPF only, reserved in eBPF */ - BPF_XADD 0xc0 /* eBPF only, exclusive add */ + BPF_IMM 0x00 /* used for 32-bit mov in classic BPF and 64-bit in eBPF */ + BPF_ABS 0x20 + BPF_IND 0x40 + BPF_MEM 0x60 + BPF_LEN 0x80 /* classic BPF only, reserved in eBPF */ + BPF_MSH 0xa0 /* classic BPF only, reserved in eBPF */ + BPF_ATOMIC 0xc0 /* eBPF only, atomic operations */ eBPF has two non-generic instructions: (BPF_ABS | <size> | BPF_LD) and (BPF_IND | <size> | BPF_LD) which are used to access packet data. @@ -1044,11 +1044,19 @@ Unlike classic BPF instruction set, eBPF has generic load/store operations:: BPF_MEM | <size> | BPF_STX: *(size *) (dst_reg + off) = src_reg BPF_MEM | <size> | BPF_ST: *(size *) (dst_reg + off) = imm32 BPF_MEM | <size> | BPF_LDX: dst_reg = *(size *) (src_reg + off) - BPF_XADD | BPF_W | BPF_STX: lock xadd *(u32 *)(dst_reg + off16) += src_reg - BPF_XADD | BPF_DW | BPF_STX: lock xadd *(u64 *)(dst_reg + off16) += src_reg -Where size is one of: BPF_B or BPF_H or BPF_W or BPF_DW. Note that 1 and -2 byte atomic increments are not supported. +Where size is one of: BPF_B or BPF_H or BPF_W or BPF_DW. + +It also includes atomic operations, which use the immediate field for extra +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 + +Note that 1 and 2 byte atomic operations are not supported. + +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. 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 |