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

PATCH Applied Wang YanQing 3 participants 3 messages Jan 24, 2018

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Wang YanQing

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#0 lore raw

PATCH 1/1 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 <[email protected]>
---
 Documentation/networking/filter.txt | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
Documentation/networking/filter.txt +1 -1
index 8781485..a4508ec 100644
@@ -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
Signature · 1 line
1.8.5.6.2.g3d8a54e.dirty
Acked-by on v1 1/1
#1 lore raw
Quoted 13 lines · Wang YanQing

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 <[email protected]>
---
 Documentation/networking/filter.txt | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
Documentation/networking/filter.txt +0 -0
index 8781485..a4508ec 100644

Documentation/networking/filter.txt The verifier's knowledge about the variable offset consists of: · line 1140

Quoted 8 lines
Documentation/networking/filter.txt +1 -1
@@ -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 <[email protected]>