[fuzzing] wasm2c integration (#2772)

This adds support for fuzzing with wabt's wasm2c that @binji wrote.
Basically we compile the wasm to C, then compile the C to a native
executable with a custom main() to wrap around it. The executable
should then print exactly the same as that wasm when run in either
the binaryen interpreter or in a JS VM with our wrapper JS for that
wasm. In other words, compiling the wasm to C is another way to
run that wasm.

The main reasons I want this are to fuzz wasm2c itself, and to
have another option for fuzzing emcc. For the latter, we do fuzz
wasm-opt quite a lot, but that doesn't fuzz the non-wasm-opt
parts of emcc. And using wasm2c for that is nice since the
starting point is always a wasm file, which means we
can use tools like wasm-reduce and so forth, which can be
integrated with this fuzzer.

This also:

Refactors the fuzzer harness a little to make it easier to
add more "VMs" to run wasms in.

Do not autoreduce when re-running a testcase, which I hit
while developing this.

1 files changed, 16 insertions, 1 deletions

diff --git a/src/tools/wasm-opt.cpp b/src/tools/wasm-opt.cpp
index c4443bde4..6fd3b7c8d 100644
--- a/src/tools/wasm-opt.cpp
+++ b/src/tools/wasm-opt.cpp
@@ -37,6 +37,7 @@
 #include "wasm-printing.h"
 #include "wasm-s-parser.h"
 #include "wasm-validator.h"
+#include "wasm2c-wrapper.h"
 
 #define DEBUG_TYPE "opt"
 
@@ -87,6 +88,7 @@ int main(int argc, const char* argv[]) {
   bool fuzzOOB = true;
   std::string emitJSWrapper;
   std::string emitSpecWrapper;
+  std::string emitWasm2CWrapper;
   std::string inputSourceMapFilename;
   std::string outputSourceMapFilename;
   std::string outputSourceMapUrl;
@@ -185,6 +187,14 @@ int main(int argc, const char* argv[]) {
          [&](Options* o, const std::string& arguments) {
            emitSpecWrapper = arguments;
          })
+    .add("--emit-wasm2c-wrapper",
+         "-esw",
+         "Emit a C wrapper file that can run the wasm after it is compiled "
+         "with wasm2c, useful for fuzzing",
+         Options::Arguments::One,
+         [&](Options* o, const std::string& arguments) {
+           emitWasm2CWrapper = arguments;
+         })
     .add("--input-source-map",
          "-ism",
          "Consume source map from the specified file",
@@ -293,13 +303,18 @@ int main(int argc, const char* argv[]) {
     outfile << generateJSWrapper(wasm);
     outfile.close();
   }
-
   if (emitSpecWrapper.size() > 0) {
     std::ofstream outfile;
     outfile.open(emitSpecWrapper, std::ofstream::out);
     outfile << generateSpecWrapper(wasm);
     outfile.close();
   }
+  if (emitWasm2CWrapper.size() > 0) {
+    std::ofstream outfile;
+    outfile.open(emitWasm2CWrapper, std::ofstream::out);
+    outfile << generateWasm2CWrapper(wasm);
+    outfile.close();
+  }
 
   std::string firstOutput;