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Commit e9dcd80b authored by Wang YanQing's avatar Wang YanQing Committed by Daniel Borkmann
Browse files

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: default avatarWang YanQing <udknight@gmail.com>
Acked-by: default avatarEdward Cree <ecree@solarflare.com>
Signed-off-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
parent 1fc0bf49

Documentation/networking/filter.txt

+1 −1
Original line number Diff line number Diff line
@@ -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