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bpf, doc: Correct one wrong value in "Register value tracking"

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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@gmail.com>
Acked-by: Edward Cree <ecree@solarflare.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
This commit is contained in:
Wang YanQing 2018-01-24 15:48:26 +08:00 committed by Daniel Borkmann
parent 1fc0bf49e4
commit e9dcd80b9d
1 changed files with 1 additions and 1 deletions
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Documentation/networking/filter.txt
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@ -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