llvm-isel-fuzzer: Handle a subset of backend flags in the executable name

Here we add a secondary option parser to llvm-isel-fuzzer (and provide
it for use with other fuzzers). With this, you can copy the fuzzer to
a name like llvm-isel-fuzzer:aarch64-gisel for a fuzzer that fuzzer
AArch64 with GlobalISel enabled, or fuzzer:x86_64 to fuzz x86, with no
flags required. This should be useful for running these in OSS-Fuzz.

Note that this handrolls a subset of cl::opts to recognize, rather
than embedding a complete command parser for argv[0]. If we find we
really need the flexibility of handling arbitrary options at some
point we can rethink this.

llvm-svn: 315545

docs/FuzzingLLVM.rst

@@ -76,6 +76,13 @@ the following command would fuzz AArch64 with :doc:`GlobalISel`:
 
    % bin/llvm-isel-fuzzer <corpus-dir> -ignore_remaining_args=1 -mtriple aarch64 -global-isel -O0
 
+Some flags can also be specified in the binary name itself in order to support
+OSS Fuzz, which has trouble with required arguments. To do this, you can copy
+or move ``llvm-isel-fuzzer`` to ``llvm-isel-fuzzer:x-y-z``, where x, y, and z
+are architecture names (``aarch64``, ``x86_64``), optimization levels (``O0``,
+``O2``), or specific keywords like ``gisel`` for enabling global instruction
+selection.
+
 llvm-mc-assemble-fuzzer
 -----------------------
 

include/llvm/FuzzMutate/FuzzerCLI.h

@@ -15,6 +15,7 @@
 #ifndef LLVM_FUZZMUTATE_FUZZER_CLI_H
 #define LLVM_FUZZMUTATE_FUZZER_CLI_H
 
+#include "llvm/ADT/StringRef.h"
 #include "llvm/Support/DataTypes.h"
 
 namespace llvm {
@@ -24,6 +25,17 @@ namespace llvm {
 /// This handles all arguments after -ignore_remaining_args=1 as cl::opts.
 void parseFuzzerCLOpts(int ArgC, char *ArgV[]);
 
+/// Handle backend options that are encoded in the executable name.
+///
+/// Parses some common backend options out of a specially crafted executable
+/// name (argv[0]). For example, a name like llvm-foo-fuzzer:aarch64-gisel might
+/// set up an AArch64 triple and the Global ISel selector. This should be called
+/// *before* parseFuzzerCLOpts if calling both.
+///
+/// This is meant to be used for environments like OSS-Fuzz that aren't capable
+/// of passing in command line arguments in the normal way.
+void handleExecNameEncodedBEOpts(StringRef ExecName);
+
 using FuzzerTestFun = int (*)(const uint8_t *Data, size_t Size);
 using FuzzerInitFun = int (*)(int *argc, char ***argv);
 

lib/FuzzMutate/FuzzerCLI.cpp

@@ -8,7 +8,7 @@
 //===----------------------------------------------------------------------===//
 
 #include "llvm/FuzzMutate/FuzzerCLI.h"
-#include "llvm/ADT/StringRef.h"
+#include "llvm/ADT/Triple.h"
 #include "llvm/Support/CommandLine.h"
 #include "llvm/Support/Compiler.h"
 #include "llvm/Support/Error.h"
@@ -31,6 +31,42 @@ void llvm::parseFuzzerCLOpts(int ArgC, char *ArgV[]) {
   cl::ParseCommandLineOptions(CLArgs.size(), CLArgs.data());
 }
 
+void llvm::handleExecNameEncodedBEOpts(StringRef ExecName) {
+  std::vector<std::string> Args{ExecName};
+
+  auto NameAndArgs = ExecName.split(':');
+  if (NameAndArgs.second.empty())
+    return;
+
+  SmallVector<StringRef, 4> Opts;
+  NameAndArgs.second.split(Opts, '-');
+  for (StringRef Opt : Opts) {
+    if (Opt.equals("gisel")) {
+      Args.push_back("-global-isel");
+      // For now we default GlobalISel to -O0
+      Args.push_back("-O0");
+    } else if (Opt.startswith("O")) {
+      Args.push_back("-" + Opt.str());
+    } else if (auto Arch = Triple::getArchTypeForLLVMName(Opt)) {
+      Args.push_back("-mtriple=" + Opt.str());
+    } else {
+      errs() << ExecName << ": Unknown option: " << Opt << ".\n";
+      exit(1);
+    }
+  }
+  errs() << NameAndArgs.first << ": Injected args:";
+  for (int I = 1, E = Args.size(); I < E; ++I)
+    errs() << " " << Args[I];
+  errs() << "\n";
+
+  std::vector<const char *> CLArgs;
+  CLArgs.reserve(Args.size());
+  for (std::string &S : Args)
+    CLArgs.push_back(S.c_str());
+
+  cl::ParseCommandLineOptions(CLArgs.size(), CLArgs.data());
+}
+
 int llvm::runFuzzerOnInputs(int ArgC, char *ArgV[], FuzzerTestFun TestOne,
                             FuzzerInitFun Init) {
   errs() << "*** This tool was not linked to libFuzzer.\n"

test/tools/llvm-isel-fuzzer/aarch64-execname-options.ll

@@ -0,0 +1,15 @@
+; REQUIRES: aarch64-registered-target
+
+; RUN: echo > %t.input
+
+; RUN: cp llvm-isel-fuzzer %t.bin:aarch64
+; RUN: %t.bin:aarch64 %t.input 2>&1 | FileCheck -check-prefix=AARCH64 %s
+; AARCH64: Injected args: -mtriple=aarch64
+
+; RUN: mv %t.bin:aarch64 %t.bin:aarch64-O1
+; RUN: %t.bin:aarch64-O1 %t.input 2>&1 | FileCheck -check-prefix=OPT-AFTER %s
+; OPT-AFTER: Injected args: -mtriple=aarch64 -O1
+
+; RUN: mv %t.bin:aarch64-O1 %t.bin:O3-aarch64
+; RUN: %t.bin:O3-aarch64 %t.input 2>&1 | FileCheck -check-prefix=OPT-BEFORE %s
+; OPT-BEFORE: Injected args: -O3 -mtriple=aarch64

test/tools/llvm-isel-fuzzer/execname-options.ll

@@ -0,0 +1,15 @@
+; RUN: echo > %t.input
+
+; RUN: cp llvm-isel-fuzzer %t.bin:gisel
+; RUN: not %t.bin:gisel %t.input 2>&1 | FileCheck -check-prefix=GISEL %s
+; GISEL: Injected args: -global-isel -O0
+; GISEL: -mtriple must be specified
+
+; RUN: cp llvm-isel-fuzzer %t.bin:gisel-O2
+; RUN: not %t.bin:gisel-O2 %t.input 2>&1 | FileCheck -check-prefix=GISEL-O2 %s
+; GISEL-O2: Injected args: -global-isel -O0 -O2
+; GISEL-O2: -mtriple must be specified
+
+; RUN: cp llvm-isel-fuzzer %t.bin:unexist
+; RUN: not %t.bin:unexist %t.input 2>&1 | FileCheck -check-prefix=NO-OPT %s
+; NO-OPT: Unknown option:

tools/llvm-isel-fuzzer/llvm-isel-fuzzer.cpp

@@ -150,6 +150,7 @@ extern "C" LLVM_ATTRIBUTE_USED int LLVMFuzzerInitialize(int *argc,
   InitializeAllAsmPrinters();
   InitializeAllAsmParsers();
 
+  handleExecNameEncodedBEOpts(*argv[0]);
   parseFuzzerCLOpts(*argc, *argv);
 
   if (TargetTriple.empty()) {