From 2b59f4dd196549bcaf8bf297fad4da6ae3e72898 Mon Sep 17 00:00:00 2001 From: Cuong Manh Le Date: Wed, 3 Aug 2022 15:14:25 +0700 Subject: [PATCH] [release-branch.go1.19] cmd/compile: correct alignment of atomic.Int64 Same as CL 417555, but for cmd/compile. Fixes #54235 Change-Id: I4cc6deaf0a87c952f636888b4ab73f81a44bfebd Reviewed-on: https://go-review.googlesource.com/c/go/+/420975 Reviewed-by: Keith Randall Reviewed-by: Matthew Dempsky Reviewed-by: Keith Randall TryBot-Result: Gopher Robot Run-TryBot: Cuong Manh Le Reviewed-on: https://go-review.googlesource.com/c/go/+/422034 Reviewed-by: Than McIntosh --- src/cmd/compile/internal/noder/sizes.go | 11 ++++++++++ src/cmd/compile/internal/types2/sizes.go | 4 ++-- test/fixedbugs/issue54220.go | 26 ++++++++++++++++++++++++ 3 files changed, 39 insertions(+), 2 deletions(-) create mode 100644 test/fixedbugs/issue54220.go diff --git a/src/cmd/compile/internal/noder/sizes.go b/src/cmd/compile/internal/noder/sizes.go index 9ba0e509d7..7820746db1 100644 --- a/src/cmd/compile/internal/noder/sizes.go +++ b/src/cmd/compile/internal/noder/sizes.go @@ -25,6 +25,17 @@ func (s *gcSizes) Alignof(T types2.Type) int64 { // is the same as unsafe.Alignof(x[0]), but at least 1." return s.Alignof(t.Elem()) case *types2.Struct: + if t.NumFields() == 0 && types2.IsSyncAtomicAlign64(T) { + // Special case: sync/atomic.align64 is an + // empty struct we recognize as a signal that + // the struct it contains must be + // 64-bit-aligned. + // + // This logic is equivalent to the logic in + // cmd/compile/internal/types/size.go:calcStructOffset + return 8 + } + // spec: "For a variable x of struct type: unsafe.Alignof(x) // is the largest of the values unsafe.Alignof(x.f) for each // field f of x, but at least 1." diff --git a/src/cmd/compile/internal/types2/sizes.go b/src/cmd/compile/internal/types2/sizes.go index 4da309461f..c99a12b2e9 100644 --- a/src/cmd/compile/internal/types2/sizes.go +++ b/src/cmd/compile/internal/types2/sizes.go @@ -53,7 +53,7 @@ func (s *StdSizes) Alignof(T Type) int64 { // is the same as unsafe.Alignof(x[0]), but at least 1." return s.Alignof(t.elem) case *Struct: - if len(t.fields) == 0 && isSyncAtomicAlign64(T) { + if len(t.fields) == 0 && IsSyncAtomicAlign64(T) { // Special case: sync/atomic.align64 is an // empty struct we recognize as a signal that // the struct it contains must be @@ -104,7 +104,7 @@ func (s *StdSizes) Alignof(T Type) int64 { return a } -func isSyncAtomicAlign64(T Type) bool { +func IsSyncAtomicAlign64(T Type) bool { named, ok := T.(*Named) if !ok { return false diff --git a/test/fixedbugs/issue54220.go b/test/fixedbugs/issue54220.go new file mode 100644 index 0000000000..105f6e9098 --- /dev/null +++ b/test/fixedbugs/issue54220.go @@ -0,0 +1,26 @@ +// run + +// Copyright 2022 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 + +import ( + "strconv" + "sync/atomic" + "unsafe" +) + +type t struct { + i1 atomic.Int32 + i2 atomic.Int64 +} + +var v t + +func main() { + if o := unsafe.Offsetof(v.i2); o != 8 { + panic("unexpected offset, want: 8, got: " + strconv.Itoa(int(o))) + } +} -- 2.48.1