1 //===--- llvm-mc-fuzzer.cpp - Fuzzer for the MC layer ---------------------===//
2 //
3 // The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 //
10 //===----------------------------------------------------------------------===//
11
12 #include "llvm-c/Disassembler.h"
13 #include "llvm-c/Target.h"
14 #include "llvm/MC/SubtargetFeature.h"
15 #include "llvm/Support/CommandLine.h"
16 #include "llvm/Support/raw_ostream.h"
17
18 using namespace llvm;
19
20 const unsigned AssemblyTextBufSize = 80;
21
22 static cl::opt<std::string>
23 TripleName("triple", cl::desc("Target triple to assemble for, "
24 "see -version for available targets"));
25
26 static cl::opt<std::string>
27 MCPU("mcpu",
28 cl::desc("Target a specific cpu type (-mcpu=help for details)"),
29 cl::value_desc("cpu-name"), cl::init(""));
30
31 // This is useful for variable-length instruction sets.
32 static cl::opt<unsigned> InsnLimit(
33 "insn-limit",
34 cl::desc("Limit the number of instructions to process (0 for no limit)"),
35 cl::value_desc("count"), cl::init(0));
36
37 static cl::list<std::string>
38 MAttrs("mattr", cl::CommaSeparated,
39 cl::desc("Target specific attributes (-mattr=help for details)"),
40 cl::value_desc("a1,+a2,-a3,..."));
41 // The feature string derived from -mattr's values.
42 std::string FeaturesStr;
43
44 static cl::list<std::string>
45 FuzzerArgs("fuzzer-args", cl::Positional,
46 cl::desc("Options to pass to the fuzzer"), cl::ZeroOrMore,
47 cl::PositionalEatsArgs);
48 static std::vector<char *> ModifiedArgv;
49
DisassembleOneInput(const uint8_t * Data,size_t Size)50 int DisassembleOneInput(const uint8_t *Data, size_t Size) {
51 char AssemblyText[AssemblyTextBufSize];
52
53 std::vector<uint8_t> DataCopy(Data, Data + Size);
54
55 LLVMDisasmContextRef Ctx = LLVMCreateDisasmCPUFeatures(
56 TripleName.c_str(), MCPU.c_str(), FeaturesStr.c_str(), nullptr, 0,
57 nullptr, nullptr);
58 assert(Ctx);
59 uint8_t *p = DataCopy.data();
60 unsigned Consumed;
61 unsigned InstructionsProcessed = 0;
62 do {
63 Consumed = LLVMDisasmInstruction(Ctx, p, Size, 0, AssemblyText,
64 AssemblyTextBufSize);
65 Size -= Consumed;
66 p += Consumed;
67
68 InstructionsProcessed ++;
69 if (InsnLimit != 0 && InstructionsProcessed < InsnLimit)
70 break;
71 } while (Consumed != 0);
72 LLVMDisasmDispose(Ctx);
73 return 0;
74 }
75
LLVMFuzzerTestOneInput(const uint8_t * Data,size_t Size)76 extern "C" int LLVMFuzzerTestOneInput(const uint8_t *Data, size_t Size) {
77 return DisassembleOneInput(Data, Size);
78 }
79
LLVMFuzzerInitialize(int * argc,char *** argv)80 extern "C" LLVM_ATTRIBUTE_USED int LLVMFuzzerInitialize(int *argc,
81 char ***argv) {
82 // The command line is unusual compared to other fuzzers due to the need to
83 // specify the target. Options like -triple, -mcpu, and -mattr work like
84 // their counterparts in llvm-mc, while -fuzzer-args collects options for the
85 // fuzzer itself.
86 //
87 // Examples:
88 //
89 // Fuzz the big-endian MIPS32R6 disassembler using 100,000 inputs of up to
90 // 4-bytes each and use the contents of ./corpus as the test corpus:
91 // llvm-mc-fuzzer -triple mips-linux-gnu -mcpu=mips32r6 -disassemble \
92 // -fuzzer-args -max_len=4 -runs=100000 ./corpus
93 //
94 // Infinitely fuzz the little-endian MIPS64R2 disassembler with the MSA
95 // feature enabled using up to 64-byte inputs:
96 // llvm-mc-fuzzer -triple mipsel-linux-gnu -mcpu=mips64r2 -mattr=msa \
97 // -disassemble -fuzzer-args ./corpus
98 //
99 // If your aim is to find instructions that are not tested, then it is
100 // advisable to constrain the maximum input size to a single instruction
101 // using -max_len as in the first example. This results in a test corpus of
102 // individual instructions that test unique paths. Without this constraint,
103 // there will be considerable redundancy in the corpus.
104
105 char **OriginalArgv = *argv;
106
107 LLVMInitializeAllTargetInfos();
108 LLVMInitializeAllTargetMCs();
109 LLVMInitializeAllDisassemblers();
110
111 cl::ParseCommandLineOptions(*argc, OriginalArgv);
112
113 // Rebuild the argv without the arguments llvm-mc-fuzzer consumed so that
114 // the driver can parse its arguments.
115 //
116 // FuzzerArgs cannot provide the non-const pointer that OriginalArgv needs.
117 // Re-use the strings from OriginalArgv instead of copying FuzzerArg to a
118 // non-const buffer to avoid the need to clean up when the fuzzer terminates.
119 ModifiedArgv.push_back(OriginalArgv[0]);
120 for (const auto &FuzzerArg : FuzzerArgs) {
121 for (int i = 1; i < *argc; ++i) {
122 if (FuzzerArg == OriginalArgv[i])
123 ModifiedArgv.push_back(OriginalArgv[i]);
124 }
125 }
126 *argc = ModifiedArgv.size();
127 *argv = ModifiedArgv.data();
128
129 // Package up features to be passed to target/subtarget
130 // We have to pass it via a global since the callback doesn't
131 // permit any user data.
132 if (MAttrs.size()) {
133 SubtargetFeatures Features;
134 for (unsigned i = 0; i != MAttrs.size(); ++i)
135 Features.AddFeature(MAttrs[i]);
136 FeaturesStr = Features.getString();
137 }
138
139 if (TripleName.empty())
140 TripleName = sys::getDefaultTargetTriple();
141
142 return 0;
143 }
144