From 516a97b3f3017ff86180acac74debde75d16186a Mon Sep 17 00:00:00 2001
From: Alex Crichton <alex@alexcrichton.com>
Date: Thu, 25 Mar 2021 18:44:04 -0500
Subject: [PATCH] A few more small fuzzing fixes (#2770)

* Increase allowances for values when fuzzing

The wasm-smith limits for generating modules are a bit higher than what
we specify, so sync those up to avoid getting too many false positives
with limits getting blown.

* Ensure fuzzing `*.wat` files are in sync

I keep looking at `*.wat` files that are actually stale, so remove stale
files if we write out a `*.wasm` file and can't disassemble it.

* Enable shadowing in dummy_linker

Fixes an issues where the same name is imported twice and we generated
two values for that. We don't mind the error here, we just want to
ignore the shadowing errors.
---
 crates/fuzzing/src/lib.rs           | 10 +++++++---
 crates/fuzzing/src/oracles.rs       | 10 +++++++---
 crates/fuzzing/src/oracles/dummy.rs |  1 +
 3 files changed, 15 insertions(+), 6 deletions(-)

diff --git a/crates/fuzzing/src/lib.rs b/crates/fuzzing/src/lib.rs
index d131149ddb..6e4e991c4c 100644
--- a/crates/fuzzing/src/lib.rs
+++ b/crates/fuzzing/src/lib.rs
@@ -39,9 +39,13 @@ pub fn fuzz_default_config(strategy: wasmtime::Strategy) -> anyhow::Result<wasmt
         .wasm_bulk_memory(true)
         .wasm_reference_types(true)
         .wasm_module_linking(true)
-        .max_instances(100)
-        .max_tables(100)
-        .max_memories(100)
+        // The limits here are chosen based on the default "maximum type size"
+        // configured in wasm-smith, which is 1000. This means that instances
+        // are allowed to, for example, export up to 1000 memories. We bump that
+        // a little bit here to give us some slop.
+        .max_instances(1100)
+        .max_tables(1100)
+        .max_memories(1100)
         .strategy(strategy)?;
     Ok(config)
 }
diff --git a/crates/fuzzing/src/oracles.rs b/crates/fuzzing/src/oracles.rs
index 3098005e06..c1f9b1e035 100644
--- a/crates/fuzzing/src/oracles.rs
+++ b/crates/fuzzing/src/oracles.rs
@@ -34,9 +34,13 @@ fn log_wasm(wasm: &[u8]) {
     let name = format!("testcase{}.wasm", i);
     std::fs::write(&name, wasm).expect("failed to write wasm file");
     log::debug!("wrote wasm file to `{}`", name);
-    if let Ok(s) = wasmprinter::print_bytes(wasm) {
-        let name = format!("testcase{}.wat", i);
-        std::fs::write(&name, s).expect("failed to write wat file");
+    let wat = format!("testcase{}.wat", i);
+    match wasmprinter::print_bytes(wasm) {
+        Ok(s) => std::fs::write(&wat, s).expect("failed to write wat file"),
+        // If wasmprinter failed remove a `*.wat` file, if any, to avoid
+        // confusing a preexisting one with this wasm which failed to get
+        // printed.
+        Err(_) => drop(std::fs::remove_file(&wat)),
     }
 }
 
diff --git a/crates/fuzzing/src/oracles/dummy.rs b/crates/fuzzing/src/oracles/dummy.rs
index 565d510cfd..f03bbfa067 100644
--- a/crates/fuzzing/src/oracles/dummy.rs
+++ b/crates/fuzzing/src/oracles/dummy.rs
@@ -6,6 +6,7 @@ use wasmtime::*;
 /// Create a set of dummy functions/globals/etc for the given imports.
 pub fn dummy_linker<'module>(store: &Store, module: &Module) -> Linker {
     let mut linker = Linker::new(store);
+    linker.allow_shadowing(true);
     for import in module.imports() {
         match import.name() {
             Some(name) => {