From a9e446b5cdb2e2ffc1c54b385b7eee5d41b53dd3 Mon Sep 17 00:00:00 2001
From: Ivan Enderlin <ivan.enderlin@hoa-project.net>
Date: Thu, 21 Nov 2019 10:51:04 +0100
Subject: [PATCH 1/3] fix(runtime-core) Fix a panic when generating globals.

Fix https://github.com/wasmerio/wasmer/issues/979.

When we try to get a global that doesn't exist, a panic is
generated. This patch just skip that path, and let a proper error be
generated later.

With this patch, we get:

```sh
$ cargo run -- run panic_index_oob_all_backends.wasm
Error: ExportNotFound { name: "main" }
```

which is kind of the expected behavior in such situation.
---
 lib/runtime-core/src/backing.rs | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/lib/runtime-core/src/backing.rs b/lib/runtime-core/src/backing.rs
index c88cb953dfb..c3118cfb00f 100644
--- a/lib/runtime-core/src/backing.rs
+++ b/lib/runtime-core/src/backing.rs
@@ -450,6 +450,11 @@ impl LocalBacking {
             let value = match &global_init.init {
                 Initializer::Const(value) => value.clone(),
                 Initializer::GetGlobal(import_global_index) => {
+                    // Skip if the global hasn't been initialized properly.
+                    if imports.globals.len() <= import_global_index.index() {
+                        continue;
+                    }
+
                     imports.globals[*import_global_index].get()
                 }
             };

From b1f58bded0925343bd322f5ab60e4b1515f12cea Mon Sep 17 00:00:00 2001
From: Ivan Enderlin <ivan.enderlin@hoa-project.net>
Date: Thu, 21 Nov 2019 10:57:52 +0100
Subject: [PATCH 2/3] fix(runtime-core) Improve error message when globals are
 corrupted.

Before this patch:

```
$ cargo run -- run panic_index_oob_all_backends.wasm
Error: ExportNotFound { name: "main" }
```

With this patch:

```sh
$ cargo run -- run panic_index_oob_all_backends.wasm
Error: Can't instantiate module: LinkError([Generic { message: "Trying to read the `0` global that isn\'t properly initialized." }])
```
---
 lib/runtime-core/src/backing.rs | 14 +++++++++-----
 1 file changed, 9 insertions(+), 5 deletions(-)

diff --git a/lib/runtime-core/src/backing.rs b/lib/runtime-core/src/backing.rs
index c3118cfb00f..1b50abaf6ab 100644
--- a/lib/runtime-core/src/backing.rs
+++ b/lib/runtime-core/src/backing.rs
@@ -77,7 +77,7 @@ impl LocalBacking {
             }
         };
         let mut tables = Self::generate_tables(module);
-        let mut globals = Self::generate_globals(module, imports);
+        let mut globals = Self::generate_globals(module, imports)?;
 
         // Ensure all initializers are valid before running finalizers
         Self::validate_memories(module, imports)?;
@@ -443,16 +443,20 @@ impl LocalBacking {
     fn generate_globals(
         module: &ModuleInner,
         imports: &ImportBacking,
-    ) -> BoxedMap<LocalGlobalIndex, Global> {
+    ) -> LinkResult<BoxedMap<LocalGlobalIndex, Global>> {
         let mut globals = Map::with_capacity(module.info.globals.len());
 
         for (_, global_init) in module.info.globals.iter() {
             let value = match &global_init.init {
                 Initializer::Const(value) => value.clone(),
                 Initializer::GetGlobal(import_global_index) => {
-                    // Skip if the global hasn't been initialized properly.
                     if imports.globals.len() <= import_global_index.index() {
-                        continue;
+                        return Err(vec![LinkError::Generic {
+                            message: format!(
+                                "Trying to read the `{:?}` global that is not properly initialized.",
+                                import_global_index.index()
+                            ),
+                        }]);
                     }
 
                     imports.globals[*import_global_index].get()
@@ -468,7 +472,7 @@ impl LocalBacking {
             globals.push(global);
         }
 
-        globals.into_boxed_map()
+        Ok(globals.into_boxed_map())
     }
 
     fn finalize_globals(

From 7313672d96c6b5fb5bfd97cdd2f69246ca63d359 Mon Sep 17 00:00:00 2001
From: Ivan Enderlin <ivan.enderlin@hoa-project.net>
Date: Thu, 21 Nov 2019 11:03:53 +0100
Subject: [PATCH 3/3] doc(changelog) Add #995.

---
 CHANGELOG.md | 1 +
 1 file changed, 1 insertion(+)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index c7b0088dc52..2696d054670 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -2,6 +2,7 @@
 
 ## **[Unreleased]**
 
+- [#995](https://github.com/wasmerio/wasmer/pull/995) Detect when a global is read without being initialized (emit a proper error instead of panicking)
 - [#992](https://github.com/wasmerio/wasmer/pull/992) Updates WAPM version to 0.4.1, fix arguments issue introduced in #990
 - [#990](https://github.com/wasmerio/wasmer/pull/990) Default wasmer CLI to `run`.  Wasmer will now attempt to parse unrecognized command line options as if they were applied to the run command: `wasmer mywasm.wasm --dir=.` now works!
 - [#987](https://github.com/wasmerio/wasmer/pull/987) Fix `runtime-c-api` header files when compiled by gnuc.