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Diffstat (limited to 'instrumentation/README.ctx.md')
| -rw-r--r-- | instrumentation/README.ctx.md | 22 |
1 files changed, 19 insertions, 3 deletions
diff --git a/instrumentation/README.ctx.md b/instrumentation/README.ctx.md index caf2c09a..ffcce0a9 100644 --- a/instrumentation/README.ctx.md +++ b/instrumentation/README.ctx.md @@ -4,14 +4,19 @@ This is an LLVM-based implementation of the context sensitive branch coverage. -Basically every function gets its own ID and that ID is combined with the -edges of the called functions. +Basically every function gets its own ID and, every time that an edge is logged, +all the IDs in the callstack are hashed and combined with the edge transition +hash to augment the classic edge coverage with the information about the +calling context. So if both function A and function B call a function C, the coverage collected in C will be different. In math the coverage is collected as follows: -`map[current_location_ID ^ previous_location_ID >> 1 ^ previous_callee_ID] += 1` +`map[current_location_ID ^ previous_location_ID >> 1 ^ hash_callstack_IDs] += 1` + +The callstack hash is produced XOR-ing the function IDs to avoid explosion with +recusrsive functions. ## Usage @@ -20,3 +25,14 @@ Set the `AFL_LLVM_INSTRUMENT=CTX` or `AFL_LLVM_CTX=1` environment variable. It is highly recommended to increase the MAP_SIZE_POW2 definition in config.h to at least 18 and maybe up to 20 for this as otherwise too many map collisions occur. + +## Caller Branch Coverage + +If the context sensitive coverage introduces too may collisions becoming +decremental, the user can choose to augment edge coverage with just the +called function ID, instead of the entire callstack hash. + +In math the coverage is collected as follows: +`map[current_location_ID ^ previous_location_ID >> 1 ^ previous_callee_ID] += 1` + +Set the `AFL_LLVM_INSTRUMENT=CALLER` or `AFL_LLVM_CALLER=1` environment variable. |