From c860edc14fda8b45323e85c2cd0f9f0365e3e8f9 Mon Sep 17 00:00:00 2001
From: Alex Crichton <alex@alexcrichton.com>
Date: Thu, 6 Feb 2020 12:04:53 -0600
Subject: [PATCH] Disable cranelift's verifier by default (#882)

The intention of the `wasmtime` crate was to disable this verifier by
default, but it looks like cranelift actually has it turned on by
default which was making our documentation incorrect!

This was discovered by seeing a number of timeouts when fuzzing. The
debug verifier is great for fuzzing, however, so fuzzing is updated to
enable this unconditionally, meaning we'll still have timeouts. For
general users though this should make the documentation correct that the
`wasmtime` crate, by default, disables the debug verifier.
---
 crates/api/src/runtime.rs     |  5 +++++
 crates/fuzzing/src/oracles.rs | 10 ++++++++--
 2 files changed, 13 insertions(+), 2 deletions(-)

diff --git a/crates/api/src/runtime.rs b/crates/api/src/runtime.rs
index a930cac462..7bc5edaf65 100644
--- a/crates/api/src/runtime.rs
+++ b/crates/api/src/runtime.rs
@@ -35,6 +35,11 @@ impl Config {
             .enable("avoid_div_traps")
             .expect("should be valid flag");
 
+        // Invert cranelift's default-on verification to instead default off.
+        flags
+            .set("enable_verifier", "false")
+            .expect("should be valid flag");
+
         Config {
             debug_info: false,
             features: Default::default(),
diff --git a/crates/fuzzing/src/oracles.rs b/crates/fuzzing/src/oracles.rs
index 5fceb66b13..e080829490 100644
--- a/crates/fuzzing/src/oracles.rs
+++ b/crates/fuzzing/src/oracles.rs
@@ -25,6 +25,7 @@ use wasmtime::*;
 pub fn instantiate(wasm: &[u8], strategy: Strategy) {
     let mut config = Config::new();
     config
+        .cranelift_debug_verifier(true)
         .strategy(strategy)
         .expect("failed to enable lightbeam");
     instantiate_with_config(wasm, config);
@@ -70,7 +71,10 @@ pub fn instantiate_with_config(wasm: &[u8], config: Config) {
 /// You can control which compiler is used via passing a `Strategy`.
 pub fn compile(wasm: &[u8], strategy: Strategy) {
     let mut config = Config::new();
-    config.strategy(strategy).unwrap();
+    config
+        .cranelift_debug_verifier(true)
+        .strategy(strategy)
+        .unwrap();
     let engine = Engine::new(&config);
     let store = Store::new(&engine);
     let _ = Module::new(&store, wasm);
@@ -264,7 +268,9 @@ pub fn make_api_calls(api: crate::generators::api::ApiCalls) {
         match call {
             ApiCall::ConfigNew => {
                 assert!(config.is_none());
-                config = Some(Config::new());
+                let mut cfg = Config::new();
+                cfg.cranelift_debug_verifier(true);
+                config = Some(cfg);
             }
 
             ApiCall::ConfigDebugInfo(b) => {