🎬 Add explicit API to run start functions; don't run it implicitly

CHANGELOG.md

@@ -2,6 +2,14 @@
 
 - Added `install_lucet_signal_handler()` and `remove_lucet_signal_handler()`, along with `Instance::ensure_signal_handler_installed()` and `Instance::ensure_sigstack_installed()` options to control the automatic installation and removal of signal handlers and alternate signal stacks. The default behaviors have not changed.
 
+- Added `Instance::run_start()` to the public API, which runs the [Wasm start function][start-function] if it is present in that instance's Wasm module. It does nothing if there is no start function.
+
+  Creating or resetting an instance no longer implicitly runs the start function. Embedders must ensure that `run_start()` is called before calling any other exported functions. `Instance::run()` will now return `Err(Error::InstanceNeedsStart)` if the start function is present but hasn't been run since the instance was created or reset.
+
+- Added a check that prevents [Wasm start functions][start-function] from calling imported functions. An instance that attempts to do so will fail with `Err(Error::RuntimeTerminated(TerminationDetails::StartCalledImportFunc))`.
+
+[start-function]: https://webassembly.github.io/spec/core/syntax/modules.html#syntax-start
+
 ### 0.6.1 (2020-02-18)
 
 - Added metadata to compiled modules that record whether instruction counting instrumentation is present.

benchmarks/lucet-benchmarks/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "lucet-benchmarks"
-version = "0.6.2-dev"
+version = "0.7.0-dev"
 description = "Benchmarks for the Lucet runtime"
 homepage = "https://github.com/fastly/lucet"
 repository = "https://github.com/fastly/lucet"

lucet-module/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "lucet-module"
-version = "0.6.2-dev"
+version = "0.7.0-dev"
 description = "A structured interface for Lucet modules"
 homepage = "https://github.com/fastly/lucet"
 repository = "https://github.com/fastly/lucet"

lucet-module/src/functions.rs

@@ -125,9 +125,15 @@ impl OwnedFunctionMetadata {
     }
 }
 
+#[derive(Clone, Copy, Debug)]
 pub struct FunctionHandle {
     pub ptr: FunctionPointer,
     pub id: FunctionIndex,
+    /// This is `true` if and only if this handle was referenced through the start section.
+    ///
+    /// The same function may be referenced via other contexts, and will appear with `false` in this
+    /// field in those cases.
+    pub is_start_func: bool,
 }
 
 // The layout of this struct is very tightly coupled to lucetc's `write_function_manifest`!

lucet-objdump/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "lucet-objdump"
-version = "0.6.2-dev"
+version = "0.7.0-dev"
 description = "Analyze object files emitted by the Lucet compiler"
 homepage = "https://github.com/fastly/lucet"
 repository = "https://github.com/fastly/lucet"
@@ -13,7 +13,7 @@ edition = "2018"
 object = "0.18"
 byteorder="1.2.1"
 colored="1.8.0"
-lucet-module = { path = "../lucet-module", version = "=0.6.2-dev" }
+lucet-module = { path = "../lucet-module", version = "=0.7.0-dev" }
 
 [package.metadata.deb]
 name = "fst-lucet-objdump"