diff options
Diffstat (limited to 'docs/env_variables.md')
| -rw-r--r-- | docs/env_variables.md | 30 |
1 files changed, 24 insertions, 6 deletions
diff --git a/docs/env_variables.md b/docs/env_variables.md index 94c34400..c47d10e8 100644 --- a/docs/env_variables.md +++ b/docs/env_variables.md @@ -10,8 +10,8 @@ Because they can't directly accept command-line options, the compile-time tools make fairly broad use of environmental variables: - - Most afl tools do not print any ouput if stout/stderr are redirected. - If you want to have the output into a file then set the AFL_DEBUG + - Most afl tools do not print any output if stdout/stderr are redirected. + If you want to save the output in a file then set the AFL_DEBUG environment variable. This is sadly necessary for various build processes which fail otherwise. @@ -44,7 +44,7 @@ tools make fairly broad use of environmental variables: you instrument hand-written assembly when compiling clang code by plugging a normalizer into the chain. (There is no equivalent feature for GCC.) - - Setting AFL_INST_RATIO to a percentage between 0 and 100% controls the + - Setting AFL_INST_RATIO to a percentage between 0% and 100% controls the probability of instrumenting every branch. This is (very rarely) useful when dealing with exceptionally complex programs that saturate the output bitmap. Examples include v8, ffmpeg, and perl. @@ -88,7 +88,7 @@ of the settings discussed in section #1, with the exception of: - TMPDIR and AFL_KEEP_ASSEMBLY, since no temporary assembly files are created. - - AFL_INST_RATIO, as we by default collision free instrumentation is used. + - AFL_INST_RATIO, as we by default use collision free instrumentation. Then there are a few specific features that are only available in llvm_mode: @@ -121,7 +121,7 @@ Then there are a few specific features that are only available in llvm_mode: None of the following options are necessary to be used and are rather for manual use (which only ever the author of this LTO implementation will use). - These are used if several seperated instrumentation are performed which + These are used if several seperated instrumentations are performed which are then later combined. - AFL_LLVM_DOCUMENT_IDS=file will document to a file which edge ID was given @@ -200,7 +200,7 @@ Then there are a few specific features that are only available in llvm_mode: ### INSTRUMENT LIST (selectively instrument files and functions) - This feature allows selectively instrumentation of the source + This feature allows selective instrumentation of the source - Setting AFL_LLVM_ALLOWLIST or AFL_LLVM_DENYLIST with a filenames and/or function will only instrument (or skip) those files that match the names @@ -278,6 +278,14 @@ checks or alter some of the more exotic semantics of the tool: don't want AFL to spend too much time classifying that stuff and just rapidly put all timeouts in that bin. + - Setting AFL_FORKSRV_INIT_TMOUT allows yout to specify a different timeout + to wait for the forkserver to spin up. The default is the `-t` value times + `FORK_WAIT_MULT` from `config.h` (usually 10), so for a `-t 100`, the + default would wait `1000` milis. Setting a different time here is useful + if the target has a very slow startup time, for example when doing + full-system fuzzing or emulation, but you don't want the actual runs + to wait too long for timeouts. + - AFL_NO_ARITH causes AFL to skip most of the deterministic arithmetics. This can be useful to speed up the fuzzing of text-based file formats. @@ -369,6 +377,16 @@ checks or alter some of the more exotic semantics of the tool: Note that this setting inhibits some of the user-friendly diagnostics normally done when starting up the forkserver and causes a pretty significant performance drop. + + - Setting AFL_MAX_DET_EXTRAS changes the count of dictionary entries/extras + (default 200), after which the entries will be used probabilistically. + So, if the dict/extras file (`-x`) contains more tokens than this threshold, + not all of the tokens will be used in each fuzzing step, every time. + Instead, there is a chance that the entry will be skipped during fuzzing. + This makes sure that the fuzzer doesn't spend all its time only inserting + the extras, but will still do other mutations. However, it decreases the + likelihood for each token to be inserted, before the next queue entry is fuzzed. + Either way, all tokens will be used eventually, in a longer fuzzing campaign. - Outdated environment variables that are that not supported anymore: AFL_DEFER_FORKSRV |