[PATCH] bpf, doc: Correct one wrong value in "Register value tracking"
From: Wang YanQing
Date: Wed Jan 24 2018 - 08:08:59 EST
If we then OR this with 0x40, then the value of 6th bit (0th is first bit)
become known, so the right mask is 0xbf instead of 0xcf.
Signed-off-by: Wang YanQing <udknight@xxxxxxxxx>
---
Documentation/networking/filter.txt | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/Documentation/networking/filter.txt b/Documentation/networking/filter.txt
index 8781485..a4508ec 100644
--- a/Documentation/networking/filter.txt
+++ b/Documentation/networking/filter.txt
@@ -1134,7 +1134,7 @@ The verifier's knowledge about the variable offset consists of:
mask and value; no bit should ever be 1 in both. For example, if a byte is read
into a register from memory, the register's top 56 bits are known zero, while
the low 8 are unknown - which is represented as the tnum (0x0; 0xff). If we
-then OR this with 0x40, we get (0x40; 0xcf), then if we add 1 we get (0x0;
+then OR this with 0x40, we get (0x40; 0xbf), then if we add 1 we get (0x0;
0x1ff), because of potential carries.
Besides arithmetic, the register state can also be updated by conditional
branches. For instance, if a SCALAR_VALUE is compared > 8, in the 'true' branch
--
1.8.5.6.2.g3d8a54e.dirty