[compiler-rt] 66df989 - [libfuzzer] Reduce default verbosity when printing large mutation sequences
Matt Morehouse via llvm-commits
llvm-commits at lists.llvm.org
Wed Sep 16 09:24:09 PDT 2020
Author: mhl
Date: 2020-09-16T09:20:57-07:00
New Revision: 66df98945e08906ce4a057245fda81f631cfd3ae
URL: https://github.com/llvm/llvm-project/commit/66df98945e08906ce4a057245fda81f631cfd3ae
DIFF: https://github.com/llvm/llvm-project/commit/66df98945e08906ce4a057245fda81f631cfd3ae.diff
LOG: [libfuzzer] Reduce default verbosity when printing large mutation sequences
When using a custom mutator (e.g. thrift mutator, similar to LPM)
that calls back into libfuzzer's mutations via `LLVMFuzzerMutate`, the mutation
sequences needed to achieve new coverage can get prohibitively large.
Printing these large sequences has two downsides:
1) It makes the logs hard to understand for a human.
2) The performance cost slows down fuzzing.
In this patch I change the `PrintMutationSequence` function to take a max
number of entries, to achieve this goal. I also update `PrintStatusForNewUnit`
to default to printing only 10 entries, in the default verbosity level (1),
requiring the user to set verbosity to 2 if they want the full mutation
sequence.
For our use case, turning off verbosity is not an option, as that would also
disable `PrintStats()` which is very useful for infrastructure that analyzes
the logs in realtime. I imagine most users of libfuzzer always want those logs
in the default.
I built a fuzzer locally with this patch applied to libfuzzer.
When running with the default verbosity, I see logs like this:
#65 NEW cov: 4799 ft: 10443 corp: 41/1447Kb lim: 64000 exec/s: 1 rss: 575Mb L: 28658/62542 MS: 196 Custom-CrossOver-ChangeBit-EraseBytes-ChangeBit-ChangeBit-ChangeBit-CrossOver-ChangeBit-CrossOver- DE: "\xff\xff\xff\x0e"-"\xfe\xff\xff\x7f"-"\xfe\xff\xff\x7f"-"\x17\x00\x00\x00\x00\x00\x00\x00"-"\x00\x00\x00\xf9"-"\xff\xff\xff\xff"-"\xfa\xff\xff\xff"-"\xf7\xff\xff\xff"-"@\xff\xff\xff\xff\xff\xff\xff"-"E\x00"-
#67 NEW cov: 4810 ft: 10462 corp: 42/1486Kb lim: 64000 exec/s: 1 rss: 577Mb L: 39823/62542 MS: 135 Custom-CopyPart-ShuffleBytes-ShuffleBytes-ChangeBit-ChangeBinInt-EraseBytes-ChangeBit-ChangeBinInt-ChangeBit- DE: "\x01\x00\x00\x00\x00\x00\x01\xf1"-"\x00\x00\x00\x07"-"\x00\x0d"-"\xfd\xff\xff\xff"-"\xfe\xff\xff\xf4"-"\xe3\xff\xff\xff"-"\xff\xff\xff\xf1"-"\xea\xff\xff\xff"-"\x00\x00\x00\xfd"-"\x01\x00\x00\x05"-
Staring hard at the logs it's clear that the cap of 10 is applied.
When running with verbosity level 2, the logs look like the below:
#66 NEW cov: 4700 ft: 10188 corp: 37/1186Kb lim: 64000 exec/s: 2 rss: 509Mb L: 47616/61231 MS: 520 Custom-CopyPart-ChangeBinInt-ChangeBit-ChangeByte-EraseBytes-PersAutoDict-CopyPart-ShuffleBytes-ChangeBit-ShuffleBytes-CopyPart-EraseBytes-CopyPart-ChangeBinInt-CopyPart-ChangeByte-ShuffleBytes-ChangeBinInt-ShuffleBytes-ChangeBit-CMP-ShuffleBytes-ChangeBit-CrossOver-ChangeBinInt-ChangeByte-ShuffleBytes-CrossOver-EraseBytes-ChangeBinInt-InsertRepeatedBytes-PersAutoDict-InsertRepeatedBytes-InsertRepeatedBytes-CrossOver-ChangeByte-ShuffleBytes-CopyPart-ShuffleBytes-CopyPart-CrossOver-ChangeBit-ShuffleBytes-CrossOver-PersAutoDict-ChangeByte-ChangeBit-ShuffleBytes-CrossOver-ChangeByte-EraseBytes-CopyPart-ChangeBinInt-PersAutoDict-CrossOver-ShuffleBytes-CrossOver-CrossOver-EraseBytes-CrossOver-EraseBytes-CrossOver-ChangeBit-ChangeBinInt-ChangeByte-EraseBytes-ShuffleBytes-ShuffleBytes-ChangeBit-EraseBytes-ChangeBinInt-ChangeBit-ChangeBinInt-CopyPart-EraseBytes-PersAutoDict-EraseBytes-CopyPart-ChangeBinInt-ChangeByte-CrossOver-ChangeBinInt-ShuffleBytes-PersAutoDict-PersAutoDict-ChangeBinInt-CopyPart-ChangeBinInt-CrossOver-ChangeBit-ChangeBinInt-CopyPart-ChangeByte-ChangeBit-CopyPart-CrossOver-ChangeByte-ChangeBit-ChangeByte-ShuffleBytes-CMP-ChangeBit-CopyPart-ChangeBit-ChangeByte-ChangeBinInt-PersAutoDict-ChangeBinInt-CrossOver-ChangeBinInt-ChangeBit-ChangeBinInt-ChangeBinInt-PersAutoDict-ChangeBinInt-ChangeBinInt-ChangeByte-CopyPart-ShuffleBytes-ChangeByte-ChangeBit-ChangeByte-ChangeByte-EraseBytes-CrossOver-ChangeByte-ChangeByte-EraseBytes-EraseBytes-InsertRepeatedBytes-ShuffleBytes-CopyPart-CopyPart-ChangeBit-ShuffleBytes-PersAutoDict-ShuffleBytes-ChangeBit-ChangeByte-ChangeBit-ShuffleBytes-ChangeByte-ChangeBinInt-CrossOver-ChangeBinInt-ChangeBit-EraseBytes-CopyPart-ChangeByte-CrossOver-EraseBytes-CrossOver-ChangeByte-ShuffleBytes-ChangeByte-ChangeBinInt-CrossOver-ChangeByte-InsertRepeatedBytes-InsertByte-ShuffleBytes-PersAutoDict-ChangeBit-ChangeByte-ChangeBit-ShuffleBytes-ShuffleBytes-CopyPart-ShuffleBytes-EraseBytes-ShuffleBytes-ShuffleBytes-CrossOver-ChangeBinInt-CopyPart-CopyPart-CopyPart-EraseBytes-EraseBytes-ChangeByte-ChangeBinInt-ShuffleBytes-CMP-InsertByte-EraseBytes-ShuffleBytes-CopyPart-ChangeBit-CrossOver-CopyPart-CopyPart-ShuffleBytes-ChangeByte-ChangeByte-ChangeBinInt-EraseBytes-ChangeByte-ChangeBinInt-ChangeBit-ChangeBit-ChangeByte-ShuffleBytes-PersAutoDict-PersAutoDict-CMP-ChangeBit-ShuffleBytes-PersAutoDict-ChangeBinInt-EraseBytes-EraseBytes-ShuffleBytes-ChangeByte-ShuffleBytes-ChangeBit-EraseBytes-CMP-ShuffleBytes-ChangeByte-ChangeBinInt-EraseBytes-ChangeBinInt-ChangeByte-EraseBytes-ChangeByte-CrossOver-ShuffleBytes-EraseBytes-EraseBytes-ShuffleBytes-ChangeBit-EraseBytes-CopyPart-ShuffleBytes-ShuffleBytes-CrossOver-CopyPart-ChangeBinInt-ShuffleBytes-CrossOver-InsertByte-InsertByte-ChangeBinInt-ChangeBinInt-CopyPart-EraseBytes-ShuffleBytes-ChangeBit-ChangeBit-EraseBytes-ChangeByte-ChangeByte-ChangeBinInt-CrossOver-ChangeBinInt-ChangeBinInt-ShuffleBytes-ShuffleBytes-ChangeByte-ChangeByte-ChangeBinInt-ShuffleBytes-CrossOver-EraseBytes-CopyPart-CopyPart-CopyPart-ChangeBit-ShuffleBytes-ChangeByte-EraseBytes-ChangeByte-InsertRepeatedBytes-InsertByte-InsertRepeatedBytes-PersAutoDict-EraseBytes-ShuffleBytes-ChangeByte-ShuffleBytes-ChangeBinInt-ShuffleBytes-ChangeBinInt-ChangeBit-CrossOver-CrossOver-ShuffleBytes-CrossOver-CopyPart-CrossOver-CrossOver-CopyPart-ChangeByte-ChangeByte-CrossOver-ChangeBit-ChangeBinInt-EraseBytes-ShuffleBytes-EraseBytes-CMP-PersAutoDict-PersAutoDict-InsertByte-ChangeBit-ChangeByte-CopyPart-CrossOver-ChangeByte-ChangeBit-ChangeByte-CopyPart-ChangeBinInt-EraseBytes-CrossOver-ChangeBit-CrossOver-PersAutoDict-CrossOver-ChangeByte-CrossOver-ChangeByte-ChangeByte-CrossOver-ShuffleBytes-CopyPart-CopyPart-ShuffleBytes-ChangeByte-ChangeByte-ChangeBinInt-ChangeBinInt-ChangeBinInt-ChangeBinInt-ShuffleBytes-CrossOver-ChangeBinInt-ShuffleBytes-ChangeBit-PersAutoDict-ChangeBinInt-ShuffleBytes-ChangeBinInt-ChangeByte-CrossOver-ChangeBit-CopyPart-ChangeBit-ChangeBit-CopyPart-ChangeByte-PersAutoDict-ChangeBit-ShuffleBytes-ChangeByte-ChangeBit-CrossOver-ChangeByte-CrossOver-ChangeByte-CrossOver-ChangeBit-ChangeByte-ChangeBinInt-PersAutoDict-CopyPart-ChangeBinInt-ChangeBit-CrossOver-ChangeBit-PersAutoDict-ShuffleBytes-EraseBytes-CrossOver-ChangeByte-ChangeBinInt-ShuffleBytes-ChangeBinInt-InsertRepeatedBytes-PersAutoDict-CrossOver-ChangeByte-Custom-PersAutoDict-CopyPart-CopyPart-ChangeBinInt-ShuffleBytes-ChangeBinInt-ChangeBit-ShuffleBytes-CrossOver-CMP-ChangeByte-CopyPart-ShuffleBytes-CopyPart-CopyPart-CrossOver-CrossOver-CrossOver-ShuffleBytes-ChangeByte-ChangeBinInt-ChangeBit-ChangeBit-ChangeBit-ChangeByte-EraseBytes-ChangeByte-ChangeBit-ChangeByte-ChangeByte-CopyPart-PersAutoDict-ChangeBinInt-PersAutoDict-PersAutoDict-PersAutoDict-CopyPart-CopyPart-CrossOver-ChangeByte-ChangeBinInt-ShuffleBytes-ChangeBit-CopyPart-EraseBytes-CopyPart-CopyPart-CrossOver-ChangeByte-EraseBytes-ShuffleBytes-ChangeByte-CopyPart-EraseBytes-CopyPart-CrossOver-ChangeBinInt-ChangeBinInt-InsertByte-ChangeBinInt-ChangeBit-ChangeByte-CopyPart-ChangeByte-EraseBytes-ChangeByte-ChangeBit-ChangeByte-ShuffleBytes-CopyPart-ChangeBinInt-EraseBytes-CrossOver-ChangeBit-ChangeBit-CrossOver-EraseBytes-ChangeBinInt-CopyPart-CopyPart-ChangeBinInt-ChangeBit-EraseBytes-InsertRepeatedBytes-EraseBytes-ChangeBit-CrossOver-CrossOver-EraseBytes-EraseBytes-ChangeByte-CopyPart-CopyPart-ShuffleBytes-ChangeByte-ChangeBit-ChangeByte-EraseBytes-ChangeBit-ChangeByte-ChangeByte-CrossOver-CopyPart-EraseBytes-ChangeByte-EraseBytes-ChangeByte-ShuffleBytes-ShuffleBytes-ChangeByte-CopyPart-ChangeByte-ChangeByte-ChangeBit-CopyPart-ChangeBit-ChangeBinInt-CopyPart-ShuffleBytes-ChangeBit-ChangeBinInt-ChangeBit-EraseBytes-CMP-CrossOver-CopyPart-ChangeBinInt-CrossOver-CrossOver-CopyPart-CrossOver-CrossOver-InsertByte-InsertByte-CopyPart-Custom- DE: "warn"-"\x00\x00\x00\x80"-"\xfe\xff\xff\xfb"-"\xff\xff"-"\x10\x00\x00\x00"-"\xfe\xff\xff\xff"-"\xff\xff\xff\xf6"-"U\x01\x00\x00\x00\x00\x00\x00"-"\xd9\xff\xff\xff"-"\xfe\xff\xff\xea"-"\xf0\xff\xff\xff"-"\xfc\xff\xff\xff"-"warn"-"\xff\xff\xff\xff"-"\xfe\xff\xff\xfb"-"\x00\x00\x00\x80"-"\xfe\xff\xff\xf1"-"\xfe\xff\xff\xea"-"\x00\x00\x00\x00\x00\x00\x012"-"\xe2\x00"-"\xfb\xff\xff\xff"-"\x00\x00\x00\x00"-"\xe9\xff\xff\xff"-"\xff\xff"-"\x00\x00\x00\x80"-"\x01\x00\x04\xc9"-"\xf0\xff\xff\xff"-"\xf9\xff\xff\xff"-"\xff\xff\xff\xff\xff\xff\xff\x12"-"\xe2\x00"-"\xfe\xff\xff\xff"-"\xfe\xff\xff\xea"-"\xff\xff\xff\xff"-"\xf4\xff\xff\xff"-"\xe9\xff\xff\xff"-"\xf1\xff\xff\xff"-
#48 NEW cov: 4502 ft: 9151 corp: 27/750Kb lim: 64000 exec/s: 2 rss: 458Mb L: 50772/50772 MS: 259 ChangeByte-ShuffleBytes-ChangeBinInt-ChangeByte-ChangeByte-ChangeByte-ChangeByte-ChangeBit-CopyPart-CrossOver-CopyPart-ChangeByte-CrossOver-CopyPart-ChangeBit-ChangeByte-EraseBytes-ChangeByte-CopyPart-CopyPart-CopyPart-ChangeBit-EraseBytes-ChangeBinInt-CrossOver-CopyPart-CrossOver-CopyPart-ChangeBit-ChangeByte-ChangeBit-InsertByte-CrossOver-InsertRepeatedBytes-InsertRepeatedBytes-InsertRepeatedBytes-ChangeBinInt-EraseBytes-InsertRepeatedBytes-InsertByte-ChangeBit-ShuffleBytes-ChangeBit-ChangeBit-CopyPart-ChangeBit-ChangeByte-CrossOver-ChangeBinInt-ChangeByte-CrossOver-CMP-ChangeByte-CrossOver-ChangeByte-ShuffleBytes-ShuffleBytes-ChangeByte-ChangeBinInt-CopyPart-EraseBytes-CrossOver-ChangeBit-ChangeBinInt-InsertByte-ChangeBit-CopyPart-ChangeBinInt-ChangeByte-CrossOver-ChangeBit-EraseBytes-CopyPart-ChangeBinInt-ChangeBit-ChangeBit-ChangeByte-CopyPart-ChangeBinInt-CrossOver-PersAutoDict-ChangeByte-ChangeBit-ChangeByte-ChangeBinInt-ChangeBinInt-EraseBytes-CopyPart-CopyPart-ChangeByte-ChangeByte-EraseBytes-PersAutoDict-CopyPart-ChangeByte-ChangeByte-EraseBytes-CrossOver-CopyPart-CopyPart-CopyPart-ChangeByte-ChangeBit-CMP-CopyPart-ChangeBinInt-ChangeBinInt-CrossOver-ChangeBit-ChangeBit-EraseBytes-ChangeByte-ShuffleBytes-ChangeBit-ChangeBinInt-CMP-InsertRepeatedBytes-CopyPart-Custom-ChangeByte-CrossOver-EraseBytes-ChangeBit-CopyPart-CrossOver-CMP-ShuffleBytes-EraseBytes-CrossOver-PersAutoDict-ChangeByte-CrossOver-CopyPart-CrossOver-CrossOver-ShuffleBytes-ChangeBinInt-CrossOver-ChangeBinInt-ShuffleBytes-PersAutoDict-ChangeByte-EraseBytes-ChangeBit-CrossOver-EraseBytes-CrossOver-ChangeBit-ChangeBinInt-EraseBytes-InsertByte-InsertRepeatedBytes-InsertByte-InsertByte-ChangeByte-ChangeBinInt-ChangeBit-CrossOver-ChangeByte-CrossOver-EraseBytes-ChangeByte-ShuffleBytes-ChangeBit-ChangeBit-ShuffleBytes-CopyPart-ChangeByte-PersAutoDict-ChangeBit-ChangeByte-InsertRepeatedBytes-CMP-CrossOver-ChangeByte-EraseBytes-ShuffleBytes-CrossOver-ShuffleBytes-ChangeBinInt-ChangeBinInt-CopyPart-PersAutoDict-ShuffleBytes-ChangeBit-CopyPart-ShuffleBytes-CopyPart-EraseBytes-ChangeByte-ChangeBit-ChangeBit-ChangeBinInt-ChangeByte-CopyPart-EraseBytes-ChangeBinInt-EraseBytes-EraseBytes-PersAutoDict-CMP-PersAutoDict-CrossOver-CrossOver-ChangeBit-CrossOver-PersAutoDict-CrossOver-CopyPart-ChangeByte-EraseBytes-ChangeByte-ShuffleBytes-ChangeByte-ChangeByte-CrossOver-ChangeBit-EraseBytes-ChangeByte-EraseBytes-ChangeBinInt-CrossOver-CrossOver-EraseBytes-ChangeBinInt-CrossOver-ChangeBit-ShuffleBytes-ChangeBit-ChangeByte-EraseBytes-ChangeBit-CrossOver-CrossOver-CrossOver-ChangeByte-ChangeBit-ShuffleBytes-ChangeBit-ChangeBit-EraseBytes-CrossOver-CrossOver-CopyPart-ShuffleBytes-ChangeByte-ChangeByte-CopyPart-CrossOver-CopyPart-CrossOver-CrossOver-EraseBytes-EraseBytes-ShuffleBytes-InsertRepeatedBytes-ChangeBit-CopyPart-Custom- DE: "\xfe\xff\xff\xfc"-"\x00\x00\x00\x00"-"F\x00"-"\xf3\xff\xff\xff"-"St9exception"-"_\x00\x00\x00"-"\xf6\xff\xff\xff"-"\xfe\xff\xff\xff"-"\x00\x00\x00\x00"-"p\x02\x00\x00\x00\x00\x00\x00"-"\xfe\xff\xff\xfb"-"\xff\xff"-"\xff\xff\xff\xff"-"\x01\x00\x00\x07"-"\xfe\xff\xff\xfe"-
These are prohibitively large and of limited value in the default case (when
someone is running the fuzzer, not debugging it), in my opinion.
Reviewed By: morehouse
Differential Revision: https://reviews.llvm.org/D86658
Added:
compiler-rt/test/fuzzer/CustomMutatorWithLongSequencesTest.cpp
Modified:
compiler-rt/lib/fuzzer/FuzzerLoop.cpp
compiler-rt/lib/fuzzer/FuzzerMutate.cpp
compiler-rt/lib/fuzzer/FuzzerMutate.h
compiler-rt/test/fuzzer/fuzzer-custommutator.test
Removed:
################################################################################
diff --git a/compiler-rt/lib/fuzzer/FuzzerLoop.cpp b/compiler-rt/lib/fuzzer/FuzzerLoop.cpp
index ce8c2fb74714..f1895ec2621a 100644
--- a/compiler-rt/lib/fuzzer/FuzzerLoop.cpp
+++ b/compiler-rt/lib/fuzzer/FuzzerLoop.cpp
@@ -636,7 +636,7 @@ void Fuzzer::PrintStatusForNewUnit(const Unit &U, const char *Text) {
PrintStats(Text, "");
if (Options.Verbosity) {
Printf(" L: %zd/%zd ", U.size(), Corpus.MaxInputSize());
- MD.PrintMutationSequence();
+ MD.PrintMutationSequence(Options.Verbosity >= 2);
Printf("\n");
}
}
diff --git a/compiler-rt/lib/fuzzer/FuzzerMutate.cpp b/compiler-rt/lib/fuzzer/FuzzerMutate.cpp
index 121b450e8b8c..cf34a9fe8e2e 100644
--- a/compiler-rt/lib/fuzzer/FuzzerMutate.cpp
+++ b/compiler-rt/lib/fuzzer/FuzzerMutate.cpp
@@ -18,6 +18,7 @@
namespace fuzzer {
const size_t Dictionary::kMaxDictSize;
+static const size_t kMaxMutationsToPrint = 10;
static void PrintASCII(const Word &W, const char *PrintAfter) {
PrintASCII(W.data(), W.size(), PrintAfter);
@@ -481,15 +482,21 @@ void MutationDispatcher::PrintRecommendedDictionary() {
Printf("###### End of recommended dictionary. ######\n");
}
-void MutationDispatcher::PrintMutationSequence() {
+void MutationDispatcher::PrintMutationSequence(bool Verbose) {
Printf("MS: %zd ", CurrentMutatorSequence.size());
- for (auto M : CurrentMutatorSequence)
- Printf("%s-", M.Name);
+ size_t EntriesToPrint =
+ Verbose ? CurrentMutatorSequence.size()
+ : std::min(kMaxMutationsToPrint, CurrentMutatorSequence.size());
+ for (size_t i = 0; i < EntriesToPrint; i++)
+ Printf("%s-", CurrentMutatorSequence[i].Name);
if (!CurrentDictionaryEntrySequence.empty()) {
Printf(" DE: ");
- for (auto DE : CurrentDictionaryEntrySequence) {
+ EntriesToPrint = Verbose ? CurrentDictionaryEntrySequence.size()
+ : std::min(kMaxMutationsToPrint,
+ CurrentDictionaryEntrySequence.size());
+ for (size_t i = 0; i < EntriesToPrint; i++) {
Printf("\"");
- PrintASCII(DE->GetW(), "\"-");
+ PrintASCII(CurrentDictionaryEntrySequence[i]->GetW(), "\"-");
}
}
}
diff --git a/compiler-rt/lib/fuzzer/FuzzerMutate.h b/compiler-rt/lib/fuzzer/FuzzerMutate.h
index 3ce3159f6893..37fd6100dac3 100644
--- a/compiler-rt/lib/fuzzer/FuzzerMutate.h
+++ b/compiler-rt/lib/fuzzer/FuzzerMutate.h
@@ -24,8 +24,9 @@ class MutationDispatcher {
~MutationDispatcher() {}
/// Indicate that we are about to start a new sequence of mutations.
void StartMutationSequence();
- /// Print the current sequence of mutations.
- void PrintMutationSequence();
+ /// Print the current sequence of mutations. Only prints the full sequence
+ /// when Verbose is true.
+ void PrintMutationSequence(bool Verbose = true);
/// Return the current sequence of mutations.
std::string MutationSequence();
/// Indicate that the current sequence of mutations was successful.
diff --git a/compiler-rt/test/fuzzer/CustomMutatorWithLongSequencesTest.cpp b/compiler-rt/test/fuzzer/CustomMutatorWithLongSequencesTest.cpp
new file mode 100644
index 000000000000..4c9714788f56
--- /dev/null
+++ b/compiler-rt/test/fuzzer/CustomMutatorWithLongSequencesTest.cpp
@@ -0,0 +1,40 @@
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+
+// Simple test for a cutom mutator that results in long sequences of mutations.
+#include <assert.h>
+#include <cstddef>
+#include <cstdint>
+#include <cstdlib>
+#include <iostream>
+#include <ostream>
+
+#include "FuzzerInterface.h"
+
+static volatile int Sink;
+
+extern "C" int LLVMFuzzerTestOneInput(const uint8_t *Data, size_t Size) {
+ assert(Data);
+ if (Size > 0 && Data[0] == 'H') {
+ Sink = 1;
+ if (Size > 1 && Data[1] == 'i') {
+ Sink = 2;
+ if (Size > 2 && Data[2] == '!') {
+ std::cout << "BINGO; Found the target, exiting\n"
+ << std::flush;
+ exit(1);
+ }
+ }
+ }
+ return 0;
+}
+
+extern "C" size_t LLVMFuzzerCustomMutator(uint8_t *Data, size_t Size,
+ size_t MaxSize, unsigned int Seed) {
+ // Run this 25 times to generate a large mutation sequence.
+ for (size_t i = 0; i < 25; i++) {
+ LLVMFuzzerMutate(Data, Size, MaxSize);
+ }
+ return LLVMFuzzerMutate(Data, Size, MaxSize);
+}
diff --git a/compiler-rt/test/fuzzer/fuzzer-custommutator.test b/compiler-rt/test/fuzzer/fuzzer-custommutator.test
index 25f5fe697b43..7d94ae064bf9 100644
--- a/compiler-rt/test/fuzzer/fuzzer-custommutator.test
+++ b/compiler-rt/test/fuzzer/fuzzer-custommutator.test
@@ -11,3 +11,17 @@ LLVMFuzzerCustomMutatorWithLenControl: INFO: found LLVMFuzzerCustomMutator
LLVMFuzzerCustomMutatorWithLenControl: In LLVMFuzzerCustomMutator
LLVMFuzzerCustomMutatorWithLenControl: {{.*}} lim: {{[1-9][0-9]?}} {{.*}}
LLVMFuzzerCustomMutatorWithLenControl: BINGO
+
+# sanity check: verify that we do get long lines with verbose printing on
+RUN: %cpp_compiler %S/CustomMutatorWithLongSequencesTest.cpp -o %t-CustomMutatorWithLongSequencesTest
+RUN: not %run %t-CustomMutatorWithLongSequencesTest -verbosity=2 2>&1 | FileCheck %s --check-prefix=LLVMFuzzerCustomMutatorLongSequence
+LLVMFuzzerCustomMutatorLongSequence: Flag: verbosity 2
+LLVMFuzzerCustomMutatorLongSequence: {{.*}} MS: {{[0-9]*}} {{(([a-zA-Z]*-){11,})}} {{.*}}
+LLVMFuzzerCustomMutatorLongSequence: BINGO
+
+# check a target that prints long mutation sequences and verifies the printed
+# output is capped at 10 entries
+RUN: not %run %t-CustomMutatorWithLongSequencesTest 2>&1 | FileCheck %s --check-prefix=LLVMFuzzerCustomMutatorLongSequenceTrimmed
+LLVMFuzzerCustomMutatorLongSequenceTrimmed-NOT: Flag: verbosity 2
+LLVMFuzzerCustomMutatorLongSequenceTrimmed-NOT: {{.*}} MS: {{[0-9]*}} {{(([a-zA-Z]*-){11,})}} {{.*}}
+LLVMFuzzerCustomMutatorLongSequenceTrimmed: BINGO
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