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| author | Arthur Fabre <arthur@arthurfabre.com> | 2018-10-07 09:45:19 +0100 |
|---|---|---|
| committer | Daniel Borkmann <daniel@iogearbox.net> | 2018-10-08 10:20:56 +0200 |
| commit | 31ce8c4a1ad26852c91de900ebf6888a4d53fc1a (patch) | |
| tree | 59dbd066ccb6f534a85b2b00d0664c0f4ea58c3a | |
| parent | 1bc38b8ff6cc54b1cd925525c0a9ffa7eef4d23b (diff) | |
| download | linux-31ce8c4a1ad26852c91de900ebf6888a4d53fc1a.tar.bz2 | |
bpf, doc: Document Jump X addressing mode
bpf_asm and the other classic BPF tools support jump conditions
comparing register A to register X, in addition to comparing
register A with constant K.
Only the latter was documented in filter.txt, add two new addressing
modes that describe the former.
Signed-off-by: Arthur Fabre <arthur@arthurfabre.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
| -rw-r--r-- | Documentation/networking/filter.txt | 30 |
1 files changed, 16 insertions, 14 deletions
diff --git a/Documentation/networking/filter.txt b/Documentation/networking/filter.txt index 4443ce958862..2196b824e96c 100644 --- a/Documentation/networking/filter.txt +++ b/Documentation/networking/filter.txt @@ -203,11 +203,11 @@ opcodes as defined in linux/filter.h stand for: Instruction Addressing mode Description - ld 1, 2, 3, 4, 10 Load word into A + ld 1, 2, 3, 4, 12 Load word into A ldi 4 Load word into A ldh 1, 2 Load half-word into A ldb 1, 2 Load byte into A - ldx 3, 4, 5, 10 Load word into X + ldx 3, 4, 5, 12 Load word into X ldxi 4 Load word into X ldxb 5 Load byte into X @@ -216,14 +216,14 @@ opcodes as defined in linux/filter.h stand for: jmp 6 Jump to label ja 6 Jump to label - jeq 7, 8 Jump on A == k - jneq 8 Jump on A != k - jne 8 Jump on A != k - jlt 8 Jump on A < k - jle 8 Jump on A <= k - jgt 7, 8 Jump on A > k - jge 7, 8 Jump on A >= k - jset 7, 8 Jump on A & k + jeq 7, 8, 9, 10 Jump on A == <x> + jneq 9, 10 Jump on A != <x> + jne 9, 10 Jump on A != <x> + jlt 9, 10 Jump on A < <x> + jle 9, 10 Jump on A <= <x> + jgt 7, 8, 9, 10 Jump on A > <x> + jge 7, 8, 9, 10 Jump on A >= <x> + jset 7, 8, 9, 10 Jump on A & <x> add 0, 4 A + <x> sub 0, 4 A - <x> @@ -240,7 +240,7 @@ opcodes as defined in linux/filter.h stand for: tax Copy A into X txa Copy X into A - ret 4, 9 Return + ret 4, 11 Return The next table shows addressing formats from the 2nd column: @@ -254,9 +254,11 @@ The next table shows addressing formats from the 2nd column: 5 4*([k]&0xf) Lower nibble * 4 at byte offset k in the packet 6 L Jump label L 7 #k,Lt,Lf Jump to Lt if true, otherwise jump to Lf - 8 #k,Lt Jump to Lt if predicate is true - 9 a/%a Accumulator A - 10 extension BPF extension + 8 x/%x,Lt,Lf Jump to Lt if true, otherwise jump to Lf + 9 #k,Lt Jump to Lt if predicate is true + 10 x/%x,Lt Jump to Lt if predicate is true + 11 a/%a Accumulator A + 12 extension BPF extension The Linux kernel also has a couple of BPF extensions that are used along with the class of load instructions by "overloading" the k argument with |