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authorArthur Fabre <arthur@arthurfabre.com>2018-10-07 09:45:19 +0100
committerDaniel Borkmann <daniel@iogearbox.net>2018-10-08 10:20:56 +0200
commit31ce8c4a1ad26852c91de900ebf6888a4d53fc1a (patch)
tree59dbd066ccb6f534a85b2b00d0664c0f4ea58c3a /Documentation/networking/filter.txt
parentlibbpf: relicense libbpf as LGPL-2.1 OR BSD-2-Clause (diff)
downloadlinux-dev-31ce8c4a1ad26852c91de900ebf6888a4d53fc1a.tar.xz
linux-dev-31ce8c4a1ad26852c91de900ebf6888a4d53fc1a.zip
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>
Diffstat (limited to '')
-rw-r--r--Documentation/networking/filter.txt30
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