Remove the jit_function_registry global state (#915)

* Remove the `jit_function_registry` global state

This commit removes on the final pieces of global state in wasmtime
today, the `jit_function_registry` module. The purpose of this module is
to help translate a native backtrace with native program counters into a
wasm backtrace with module names, function names, and wasm module
indices. To that end this module retained a global map of function
ranges to this metadata information for each compiled function.

It turns out that we already had a `NAMES` global in the `wasmtime`
crate for symbolicating backtrace addresses, so this commit moves that
global into its own file and restructures the internals to account for
program counter ranges as well. The general set of changes here are:

* Remove `jit_function_registry`
* Remove `NAMES`
* Create a new `frame_info` module which has a singleton global
  registering compiled module's frame information.
* Update traps to use the `frame_info` module to symbolicate pcs,
  directly extracting a `FrameInfo` from the module.
* Register and unregister information on a module level instead of on a
  per-function level (at least in terms of locking granluarity).

This commit leaves the new `FRAME_INFO` global variable as the only
remaining "critical" global variable in `wasmtime`, which only exists
due to the API of `Trap` where it doesn't take in any extra context when
capturing a stack trace through which we could hang off frame
information. I'm thinking though that this is ok, and we can always
tweak the API of `Trap` in the future if necessary if we truly need to
accomodate this.

* Remove a lazy_static dep

* Add some comments and restructure

crates/jit/src/instantiate.rs

@@ -48,7 +48,7 @@ pub enum SetupError {
 /// from the wasm buffer rather than holding its own copy.
 struct RawCompiledModule<'data> {
     module: Module,
-    finished_functions: BoxedSlice<DefinedFuncIndex, *const VMFunctionBody>,
+    finished_functions: BoxedSlice<DefinedFuncIndex, *mut [VMFunctionBody]>,
     data_initializers: Box<[DataInitializer<'data>]>,
     signatures: BoxedSlice<SignatureIndex, VMSharedSignatureIndex>,
     dbg_jit_registration: Option<GdbJitImageRegistration>,
@@ -74,7 +74,7 @@ impl<'data> RawCompiledModule<'data> {
             None
         };
 
-        let (allocated_functions, jt_offsets, relocations, dbg_image, trap_registration) = compiler
+        let (finished_functions, jt_offsets, relocations, dbg_image, trap_registration) = compiler
             .compile(
                 &translation.module,
                 translation.module_translation.as_ref().unwrap(),
@@ -84,22 +84,11 @@ impl<'data> RawCompiledModule<'data> {
 
         link_module(
             &translation.module,
-            &allocated_functions,
+            &finished_functions,
             &jt_offsets,
             relocations,
         );
 
-        // Gather up the pointers to the compiled functions.
-        let finished_functions: BoxedSlice<DefinedFuncIndex, *const VMFunctionBody> =
-            allocated_functions
-                .into_iter()
-                .map(|(_index, allocated)| {
-                    let fatptr: *const [VMFunctionBody] = *allocated;
-                    fatptr as *const VMFunctionBody
-                })
-                .collect::<PrimaryMap<_, _>>()
-                .into_boxed_slice();
-
         // Compute indices into the shared signature table.
         let signatures = {
             let signature_registry = compiler.signatures();
@@ -125,7 +114,7 @@ impl<'data> RawCompiledModule<'data> {
 
         Ok(Self {
             module: translation.module,
-            finished_functions,
+            finished_functions: finished_functions.into_boxed_slice(),
             data_initializers: translation.data_initializers.into_boxed_slice(),
             signatures: signatures.into_boxed_slice(),
             dbg_jit_registration,
@@ -137,7 +126,7 @@ impl<'data> RawCompiledModule<'data> {
 /// A compiled wasm module, ready to be instantiated.
 pub struct CompiledModule {
     module: Arc<Module>,
-    finished_functions: BoxedSlice<DefinedFuncIndex, *const VMFunctionBody>,
+    finished_functions: BoxedSlice<DefinedFuncIndex, *mut [VMFunctionBody]>,
     data_initializers: Box<[OwnedDataInitializer]>,
     signatures: BoxedSlice<SignatureIndex, VMSharedSignatureIndex>,
     dbg_jit_registration: Option<Rc<GdbJitImageRegistration>>,
@@ -170,7 +159,7 @@ impl CompiledModule {
     /// Construct a `CompiledModule` from component parts.
     pub fn from_parts(
         module: Module,
-        finished_functions: BoxedSlice<DefinedFuncIndex, *const VMFunctionBody>,
+        finished_functions: BoxedSlice<DefinedFuncIndex, *mut [VMFunctionBody]>,
         data_initializers: Box<[OwnedDataInitializer]>,
         signatures: BoxedSlice<SignatureIndex, VMSharedSignatureIndex>,
         dbg_jit_registration: Option<GdbJitImageRegistration>,
@@ -229,6 +218,11 @@ impl CompiledModule {
     pub fn module_ref(&self) -> &Module {
         &self.module
     }
+
+    /// Returns the map of all finished JIT functions compiled for this module
+    pub fn finished_functions(&self) -> &BoxedSlice<DefinedFuncIndex, *mut [VMFunctionBody]> {
+        &self.finished_functions
+    }
 }
 
 /// Similar to `DataInitializer`, but owns its own copy of the data rather