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Date: Sun, 7 Oct 2018 09:45:19 +0100
From: Arthur Fabre <arthur@...hurfabre.com>
To: Alexei Starovoitov <ast@...nel.org>,
Daniel Borkmann <daniel@...earbox.net>,
"David S. Miller" <davem@...emloft.net>,
Jonathan Corbet <corbet@....net>, netdev@...r.kernel.org,
linux-doc@...r.kernel.org
Cc: Arthur Fabre <arthur@...hurfabre.com>
Subject: [PATCH] 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@...hurfabre.com>
---
Documentation/networking/filter.txt | 30 +++++++++++++++--------------
1 file changed, 16 insertions(+), 14 deletions(-)
diff --git a/Documentation/networking/filter.txt b/Documentation/networking/filter.txt
index e6b4ebb2b243..b90dad6fea6d 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
--
2.19.1
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