[llvm-mc-fuzzer] Support untested instruction discovery for variable length instruction sets like microMIPS.
Summary:
For fixed length instructions, we can use -max_len to limit the fuzzer to a
single instruction. This doesn't work for variable length instruction sets
since a 4-byte input could consist of one 4-byte instruction or two 2-byte
instructions.
This patch adds a --insn-limit to llvm-mc-fuzzer to limit the input in
terms of instructions processed.
Reviewers: kcc
Subscribers: kcc, llvm-commits
Differential Revision: http://reviews.llvm.org/D12960
llvm-svn: 248253
diff --git a/llvm/tools/llvm-mc-fuzzer/llvm-mc-fuzzer.cpp b/llvm/tools/llvm-mc-fuzzer/llvm-mc-fuzzer.cpp
index 7b89132..f2bbe4f 100644
--- a/llvm/tools/llvm-mc-fuzzer/llvm-mc-fuzzer.cpp
+++ b/llvm/tools/llvm-mc-fuzzer/llvm-mc-fuzzer.cpp
@@ -44,6 +44,12 @@
cl::desc("Target a specific cpu type (-mcpu=help for details)"),
cl::value_desc("cpu-name"), cl::init(""));
+// This is useful for variable-length instruction sets.
+static cl::opt<unsigned> InsnLimit(
+ "insn-limit",
+ cl::desc("Limit the number of instructions to process (0 for no limit)"),
+ cl::value_desc("count"), cl::init(0));
+
static cl::list<std::string>
MAttrs("mattr", cl::CommaSeparated,
cl::desc("Target specific attributes (-mattr=help for details)"),
@@ -67,11 +73,16 @@
assert(Ctx);
uint8_t *p = DataCopy.data();
unsigned Consumed;
+ unsigned InstructionsProcessed = 0;
do {
Consumed = LLVMDisasmInstruction(Ctx, p, Size, 0, AssemblyText,
AssemblyTextBufSize);
Size -= Consumed;
p += Consumed;
+
+ InstructionsProcessed ++;
+ if (InsnLimit != 0 && InstructionsProcessed < InsnLimit)
+ break;
} while (Consumed != 0);
LLVMDisasmDispose(Ctx);
}