Procs

proc customCrossOver(data1: ptr UncheckedArray[byte]; len1: int;
                     data2: ptr UncheckedArray[byte]; len2: int;
                     res: ptr UncheckedArray[byte]; maxResLen: int; seed: int64): int {.
    exportc: "LLVMFuzzerCustomCrossOver", ...raises: [], tags: [], forbids: [].}

Optional user-provided custom cross-over procedure. Combines pieces of data1 & data2 together into res. Returns the new length, which is not greater than maxResLen. Should produce the same mutation given the same seed. Source   Edit  

proc customMutator(data: ptr UncheckedArray[byte]; len, maxLen: int; seed: int64): int {.
    exportc: "LLVMFuzzerCustomMutator", ...raises: [], tags: [], forbids: [].}

Optional user-provided custom mutator. Mutates raw data in data[0..<len] inplace. Returns the new length, which is not greater than maxLen. Given the same seed produces the same mutation. Source   Edit  

proc initialize(): cint {.exportc: "LLVMFuzzerInitialize", ...raises: [], tags: [],
                          forbids: [].}

Initialize Nim's internals, which is done calling a NimMain function. Source   Edit  

proc mutate(data: ptr UncheckedArray[byte]; len, maxLen: int): int {.
    importc: "LLVMFuzzerMutate", ...raises: [], tags: [], forbids: [].}

Experimental, may go away in future. libFuzzer-provided procedure to be used inside customMutator. Mutates raw data in data[0..<len] inplace. Returns the new length, which is not greater than maxLen. Source   Edit  

proc standaloneFuzzTarget() {....raises: [IOError, ValueError],
                              tags: [WriteIOEffect, ReadIOEffect], forbids: [].}

Standalone main procedure for fuzz targets.

Use -d:fuzzSa to call standaloneFuzzTarget to provide reproducers for bugs when linking against libFuzzer is undesirable.

Source   Edit  

proc testOneInput(data: ptr UncheckedArray[byte]; len: int): cint {.
    exportc: "LLVMFuzzerTestOneInput", ...raises: [], tags: [], forbids: [].}

Mandatory user-provided target procedure. Executes the code under test with data as the input. libFuzzer will invoke this procedure many times with different inputs. Must return 0. Source   Edit