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

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