Windows FPRs preservation (#1216)

Preserve FPRs as required by the Windows fastcall calling convention.

This exposes an implementation limit due to Cranelift's approach to stack layout, which conflicts with expectations Windows makes in SEH layout - functions where the Cranelift user desires fastcall unwind information, that require preservation of an ABI-reserved FPR, that have a stack frame 240 bytes or larger, now produce an error when compiled. Several wasm spectests were disabled because they would trip this limit. This is a temporary constraint that should be fixed promptly.

Co-authored-by: bjorn3 <bjorn3@users.noreply.github.com>

build.rs

@@ -194,6 +194,17 @@ fn ignore(testsuite: &str, testname: &str, strategy: &str) -> bool {
             ("reference_types", "table_copy_on_imported_tables") => return false,
             ("reference_types", _) => return true,
 
+            ("misc_testsuite", "export_large_signature")
+            | ("spec_testsuite", "call")
+            | ("multi_value", "call")
+            | ("multi_value", "func") => {
+                // FIXME These involves functions with very large stack frames that Cranelift currently
+                // cannot compile using the fastcall (Windows) calling convention.
+                // See https://github.com/bytecodealliance/wasmtime/pull/1216.
+                #[cfg(windows)]
+                return true;
+            }
+
             _ => {}
         },
         _ => panic!("unrecognized strategy"),

cranelift/codegen/src/context.rs

@@ -206,8 +206,8 @@ impl Context {
         isa: &dyn TargetIsa,
         kind: FrameUnwindKind,
         sink: &mut dyn FrameUnwindSink,
-    ) {
-        isa.emit_unwind_info(&self.func, kind, sink);
+    ) -> CodegenResult<()> {
+        isa.emit_unwind_info(&self.func, kind, sink)
     }
 
     /// Run the verifier on the function.

cranelift/codegen/src/isa/mod.rs

@@ -398,8 +398,9 @@ pub trait TargetIsa: fmt::Display + Send + Sync {
         _func: &ir::Function,
         _kind: binemit::FrameUnwindKind,
         _sink: &mut dyn binemit::FrameUnwindSink,
-    ) {
+    ) -> CodegenResult<()> {
         // No-op by default
+        Ok(())
     }
 }
 

cranelift/codegen/src/isa/x86/fde.rs

@@ -4,6 +4,7 @@ use crate::binemit::{FrameUnwindOffset, FrameUnwindSink, Reloc};
 use crate::ir::{FrameLayoutChange, Function};
 use crate::isa::fde::RegisterMappingError;
 use crate::isa::{CallConv, RegUnit, TargetIsa};
+use crate::result::CodegenResult;
 use alloc::vec::Vec;
 use core::convert::TryInto;
 use gimli::write::{
@@ -178,7 +179,11 @@ fn to_cfi(
 }
 
 /// Creates FDE structure from FrameLayout.
-pub fn emit_fde(func: &Function, isa: &dyn TargetIsa, sink: &mut dyn FrameUnwindSink) {
+pub fn emit_fde(
+    func: &Function,
+    isa: &dyn TargetIsa,
+    sink: &mut dyn FrameUnwindSink,
+) -> CodegenResult<()> {
     assert!(isa.name() == "x86");
 
     // Expecting function with System V prologue
@@ -266,6 +271,8 @@ pub fn emit_fde(func: &Function, isa: &dyn TargetIsa, sink: &mut dyn FrameUnwind
 
     // Need 0 marker for GCC unwind to end FDE "list".
     sink.bytes(&[0, 0, 0, 0]);
+
+    Ok(())
 }
 
 #[cfg(test)]
@@ -314,7 +321,7 @@ mod tests {
         context.compile(&*isa).expect("expected compilation");
 
         let mut sink = SimpleUnwindSink(Vec::new(), 0, Vec::new());
-        emit_fde(&context.func, &*isa, &mut sink);
+        emit_fde(&context.func, &*isa, &mut sink).expect("can emit fde");
 
         assert_eq!(
             sink.0,
@@ -376,7 +383,7 @@ mod tests {
         context.compile(&*isa).expect("expected compilation");
 
         let mut sink = SimpleUnwindSink(Vec::new(), 0, Vec::new());
-        emit_fde(&context.func, &*isa, &mut sink);
+        emit_fde(&context.func, &*isa, &mut sink).expect("can emit fde");
 
         assert_eq!(
             sink.0,

cranelift/codegen/src/isa/x86/mod.rs

@@ -177,8 +177,8 @@ impl TargetIsa for Isa {
         func: &ir::Function,
         kind: FrameUnwindKind,
         sink: &mut dyn FrameUnwindSink,
-    ) {
-        abi::emit_unwind_info(func, self, kind, sink);
+    ) -> CodegenResult<()> {
+        abi::emit_unwind_info(func, self, kind, sink)
     }
 }