[EH] Fuzz throws from JS (#7027)

We already generated (throw ..) instructions in wasm, but it makes sense to model
throws from outside as well, as they cross the module boundary. This adds a new fuzzer
import to the generated modules, "throw", that just does a throw from JS etc.

Also be more precise about handling fuzzing-support imports in fuzz-exec: we now
check that logging functions start with "log*" and error otherwise (this check is
now needed given we have "throw", which is not logging). Also fix a minor issue
with name conflicts for logging functions by using getValidFunctionName for them,
both for logging and for throw.

1 files changed, 7 insertions, 0 deletions

diff --git a/scripts/fuzz_shell.js b/scripts/fuzz_shell.js
index 3d29b197c..4cf3ba358 100644
--- a/scripts/fuzz_shell.js
+++ b/scripts/fuzz_shell.js
@@ -138,6 +138,7 @@ function logValue(x, y) {
 var tempRet0;
 var imports = {
   'fuzzing-support': {
+    // Logging.
     'log-i32': logValue,
     'log-i64': logValue,
     'log-f32': logValue,
@@ -147,7 +148,13 @@ var imports = {
     // we could avoid running JS on code with SIMD in it, but it is useful to
     // fuzz such code as much as we can.)
     'log-v128': logValue,
+
+    // Throw an exception from JS.
+    'throw': () => {
+      throw 'some JS error';
+    }
   },
+  // Emscripten support.
   'env': {
     'setTempRet0': function(x) { tempRet0 = x },
     'getTempRet0': function() { return tempRet0 },