Re: [PATCH] bpf, doc: Correct one wrong value in "Register value tracking"
On 01/24/2018 08:48 AM, Wang YanQing wrote: > 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 Applied to bpf-next, thanks Wang!
Re: [PATCH] bpf, doc: Correct one wrong value in "Register value tracking"
On 24/01/18 07:48, Wang YanQing wrote: > 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 > --- > 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 Acked-by: Edward Cree
[PATCH] 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 --- 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
