Plumb the winch calling convention through Tunables

crates/cranelift/src/lib.rs

@@ -153,6 +153,15 @@ fn wasm_call_signature(
             CallConv::Tail
         }
 
+        // The winch calling convention is only implemented for x64 and aarch64
+        arch if tunables.tail_callable => {
+            assert!(
+                matches!(arch, Architecture::X86_64 | Architecture::Aarch64(_)),
+                "https://github.com/bytecodealliance/wasmtime/issues/6530"
+            );
+            CallConv::Winch
+        }
+
         // On s390x the "wasmtime" calling convention is used to give vectors
         // little-endian lane order at the ABI layer which should reduce the
         // need for conversion when operating on vector function arguments. By

crates/environ/src/tunables.rs

@@ -56,6 +56,9 @@ pub struct Tunables {
 
     /// Whether or not Wasm functions can be tail-called or not.
     pub tail_callable: bool,
+
+    /// Whether or not Wasm functions target the winch abi.
+    pub winch_callable: bool,
 }
 
 impl Tunables {
@@ -106,6 +109,7 @@ impl Tunables {
             debug_adapter_modules: false,
             relaxed_simd_deterministic: false,
             tail_callable: false,
+            winch_callable: false,
         }
     }
 

crates/wasmtime/src/config.rs

@@ -1719,6 +1719,13 @@ impl Config {
             tail_callable
         }
 
+        // If we're going to compile with winch, we must use the winch calling convention.
+        tunables.winch_callable = match self.compiler_config.strategy {
+            Strategy::Auto => !cfg!(feature = "cranelift") && cfg!(feature = "winch"),
+            Strategy::Cranelift => false,
+            Strategy::Winch => true,
+        };
+
         if tunables.static_memory_offset_guard_size < tunables.dynamic_memory_offset_guard_size {
             bail!("static memory guard size cannot be smaller than dynamic memory guard size");
         }

crates/wasmtime/src/engine/serialization.rs

@@ -341,6 +341,7 @@ impl Metadata<'_> {
             guard_before_linear_memory,
             relaxed_simd_deterministic,
             tail_callable,
+            winch_callable,
 
             // This doesn't affect compilation, it's just a runtime setting.
             dynamic_memory_growth_reserve: _,
@@ -402,6 +403,11 @@ impl Metadata<'_> {
             "relaxed simd deterministic semantics",
         )?;
         Self::check_bool(tail_callable, other.tail_callable, "WebAssembly tail calls")?;
+        Self::check_bool(
+            winch_callable,
+            other.winch_callable,
+            "Winch calling convention",
+        )?;
 
         Ok(())
     }

crates/winch/src/builder.rs

@@ -48,6 +48,7 @@ impl CompilerBuilder for Builder {
     }
 
     fn set_tunables(&mut self, tunables: wasmtime_environ::Tunables) -> Result<()> {
+        assert!(tunables.winch_callable);
         self.cranelift.set_tunables(tunables)?;
         Ok(())
     }