cmd/compile: remove races introduced in abiutils field update

This fix uses mutex around the problematic store and subsequent access;
if this causes performance problems later a better fix is to do all the
ABI binding in gc/walk where it is single-threaded.

Change-Id: I488f28ab75beb8351c856fd50b0095cab463642e
Reviewed-on: https://go-review.googlesource.com/c/go/+/298109
Trust: David Chase <drchase@google.com>
Run-TryBot: David Chase <drchase@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Austin Clements <austin@google.com>

2 files changed, 26 insertions, 7 deletions

diff --git a/src/cmd/compile/internal/abi/abiutils.go b/src/cmd/compile/internal/abi/abiutils.go
index 903cc5205d..3eab4b8d8b 100644
--- a/src/cmd/compile/internal/abi/abiutils.go
+++ b/src/cmd/compile/internal/abi/abiutils.go
@@ -315,12 +315,31 @@ func (config *ABIConfig) ABIAnalyze(t *types.Type) *ABIParamResultInfo {
 	return result
 }
 
+// parameterUpdateMu protects the Offset field of function/method parameters (a subset of structure Fields)
+var parameterUpdateMu sync.Mutex
+
+// FieldOffsetOf returns a concurency-safe version of f.Offset
+func FieldOffsetOf(f *types.Field) int64 {
+	parameterUpdateMu.Lock()
+	defer parameterUpdateMu.Unlock()
+	return f.Offset
+}
+
 func (config *ABIConfig) updateOffset(result *ABIParamResultInfo, f *types.Field, a ABIParamAssignment, isReturn bool) {
 	// Everything except return values in registers has either a frame home (if not in a register) or a frame spill location.
 	if !isReturn || len(a.Registers) == 0 {
 		// The type frame offset DOES NOT show effects of minimum frame size.
 		// Getting this wrong breaks stackmaps, see liveness/plive.go:WriteFuncMap and typebits/typebits.go:Set
-		f.Offset = a.FrameOffset(result)-config.LocalsOffset()
+		parameterUpdateMu.Lock()
+		defer parameterUpdateMu.Unlock()
+		off := a.FrameOffset(result) - config.LocalsOffset()
+		fOffset := f.Offset
+		if fOffset == types.BOGUS_FUNARG_OFFSET {
+			// Set the Offset the first time. After that, we may recompute it, but it should never change.
+			f.Offset = off
+		} else if fOffset != off {
+			panic(fmt.Errorf("Offset changed from %d to %d", fOffset, off))
+		}
 	}
 }
 
diff --git a/src/cmd/compile/internal/ssagen/ssa.go b/src/cmd/compile/internal/ssagen/ssa.go
index f4da71fef4..05dd0c62a9 100644
--- a/src/cmd/compile/internal/ssagen/ssa.go
+++ b/src/cmd/compile/internal/ssagen/ssa.go
@@ -1240,7 +1240,7 @@ func (s *state) instrumentFields(t *types.Type, addr *ssa.Value, kind instrument
 		if f.Sym.IsBlank() {
 			continue
 		}
-		offptr := s.newValue1I(ssa.OpOffPtr, types.NewPtr(f.Type), f.Offset, addr)
+		offptr := s.newValue1I(ssa.OpOffPtr, types.NewPtr(f.Type), abi.FieldOffsetOf(f), addr)
 		s.instrumentFields(f.Type, offptr, kind)
 	}
 }
@@ -4759,7 +4759,7 @@ func (s *state) openDeferExit() {
 		}
 		for j, argAddrVal := range r.argVals {
 			f := getParam(r.n, j)
-			ACArgs = append(ACArgs, ssa.Param{Type: f.Type, Offset: int32(argStart + f.Offset)})
+			ACArgs = append(ACArgs, ssa.Param{Type: f.Type, Offset: int32(argStart + abi.FieldOffsetOf(f))})
 			var a *ssa.Value
 			if !TypeOK(f.Type) {
 				a = s.newValue2(ssa.OpDereference, f.Type, argAddrVal, s.mem())
@@ -4867,12 +4867,12 @@ func (s *state) call(n *ir.CallExpr, k callKind, returnResultAddr bool) *ssa.Val
 	types.CalcSize(fn.Type())
 	stksize := fn.Type().ArgWidth() // includes receiver, args, and results
 
-	abi := s.f.ABI1
+	callABI := s.f.ABI1
 	if !inRegisters {
-		abi = s.f.ABI0
+		callABI = s.f.ABI0
 	}
 
-	params := abi.ABIAnalyze(n.X.Type())
+	params := callABI.ABIAnalyze(n.X.Type())
 
 	res := n.X.Type().Results()
 	if k == callNormal {
@@ -4933,7 +4933,7 @@ func (s *state) call(n *ir.CallExpr, k callKind, returnResultAddr bool) *ssa.Val
 		}
 		// Set other args.
 		for _, f := range ft.Params().Fields().Slice() {
-			s.storeArgWithBase(args[0], f.Type, addr, off+f.Offset)
+			s.storeArgWithBase(args[0], f.Type, addr, off+abi.FieldOffsetOf(f))
 			args = args[1:]
 		}