cmd/compile: fix register/offset calculation for trailing empty field case.

Includes test.
Long term, need to make the offending code be more in terms
of official types package offsets, instead of duplicating that
logic.

For #40724.

Change-Id: Id33a153f10aed3289cc48d1f99a8e0f6ece9474d
Reviewed-on: https://go-review.googlesource.com/c/go/+/306469
Trust: David Chase <drchase@google.com>
Run-TryBot: David Chase <drchase@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Than McIntosh <thanm@google.com>
Reviewed-by: Cherry Zhang <cherryyz@google.com>

diff --git a/src/cmd/compile/internal/abi/abiutils.go b/src/cmd/compile/internal/abi/abiutils.go
index 56e008830fe3f8524ce3ae43a7c3591c140445fd..50a818c025cc63bfb3b9acfb7924856322e75e53 100644 (file)
--- a/src/cmd/compile/internal/abi/abiutils.go
+++ b/src/cmd/compile/internal/abi/abiutils.go
@@ -211,8 +211,11 @@ func appendParamOffsets(offsets []int64, at int64, t *types.Type) ([]int64, int6
                                offsets, at = appendParamOffsets(offsets, at, t.Elem())
                        }
                case types.TSTRUCT:
-                       for _, f := range t.FieldSlice() {
+                       for i, f := range t.FieldSlice() {
                                offsets, at = appendParamOffsets(offsets, at, f.Type)
+                               if f.Type.Width == 0 && i == t.NumFields()-1 {
+                                       at++ // last field has zero width
+                               }
                        }
                        at = align(at, t) // type size is rounded up to its alignment
                case types.TSLICE:

diff --git a/test/abi/fuzz_trailing_zero_field.go b/test/abi/fuzz_trailing_zero_field.go
new file mode 100644 (file)
index 0000000..ae7ad32
--- /dev/null
+++ b/test/abi/fuzz_trailing_zero_field.go
@@ -0,0 +1,39 @@
+// run
+
+// Copyright 2021 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package main
+
+var p0exp = S1{
+       F1: complex(float64(2.3640607624715027), float64(-0.2717825524109192)),
+       F2: S2{F1: 9},
+       F3: 103050709,
+}
+
+type S1 struct {
+       F1 complex128
+       F2 S2
+       F3 uint64
+}
+
+type S2 struct {
+       F1 uint64
+       F2 empty
+}
+
+type empty struct {
+}
+
+//go:noinline
+//go:registerparams
+func callee(p0 S1) {
+       if p0 != p0exp {
+               panic("bad p0")
+       }
+}
+
+func main() {
+       callee(p0exp)
+}