cmd/compile: add structs.HostLayout

This is for the proposal, plus a few bug fixes
that would/will be necessary when this is put into
actual use.

Fixes #66408.
Updates #63131.

Change-Id: I3a66e09d707dd579c59f155e7f53367f41214c30
Reviewed-on: https://go-review.googlesource.com/c/go/+/578355
Reviewed-by: Austin Clements <austin@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: David Chase <drchase@google.com>

diff --git a/api/next/66408.txt b/api/next/66408.txt
new file mode 100644 (file)
index 0000000..32147bd
--- /dev/null
+++ b/api/next/66408.txt
@@ -0,0 +1 @@
+pkg structs, type HostLayout struct #66408

diff --git a/doc/next/6-stdlib/3-structs.md b/doc/next/6-stdlib/3-structs.md
new file mode 100644 (file)
index 0000000..1f0de8f
--- /dev/null
+++ b/doc/next/6-stdlib/3-structs.md
@@ -0,0 +1,12 @@
+### New structs package
+
+
+The new [structs](/pkg/structs) package provides
+types for struct fields that modify properties of
+the containing struct type such as memory layout.
+
+In this release, the only such type is
+[`HostLayout`](/pkg/structs#HostLayout)
+which indicates that a structure with a field of that
+type has a layout that conforms to host platform
+expectations.
\ No newline at end of file

diff --git a/doc/next/6-stdlib/99-minor/structs/66408.md b/doc/next/6-stdlib/99-minor/structs/66408.md
new file mode 100644 (file)
index 0000000..810a09e
--- /dev/null
+++ b/doc/next/6-stdlib/99-minor/structs/66408.md
@@ -0,0 +1 @@
+<!-- This is a new package; covered in 6-stdlib/3-structs.md. -->

diff --git a/src/cmd/compile/internal/abi/abiutils.go b/src/cmd/compile/internal/abi/abiutils.go
index 607d462493e9f0b17d3f365babe2a62141f05046..e88a80d564623d2030af0c812e2dcc3583bbb755 100644 (file)
--- a/src/cmd/compile/internal/abi/abiutils.go
+++ b/src/cmd/compile/internal/abi/abiutils.go
@@ -141,7 +141,7 @@ func (pa *ABIParamAssignment) RegisterTypesAndOffsets() ([]*types.Type, []int64)
        }
        typs := make([]*types.Type, 0, l)
        offs := make([]int64, 0, l)
-       offs, _ = appendParamOffsets(offs, 0, pa.Type)
+       offs, _ = appendParamOffsets(offs, 0, pa.Type) // 0 is aligned for everything.
        return appendParamTypes(typs, pa.Type), offs
 }
 
@@ -193,8 +193,8 @@ func appendParamTypes(rts []*types.Type, t *types.Type) []*types.Type {
 
 // appendParamOffsets appends the offset(s) of type t, starting from "at",
 // to input offsets, and returns the longer slice and the next unused offset.
+// at should already be aligned for t.
 func appendParamOffsets(offsets []int64, at int64, t *types.Type) ([]int64, int64) {
-       at = align(at, t)
        w := t.Size()
        if w == 0 {
                return offsets, at
@@ -210,11 +210,15 @@ func appendParamOffsets(offsets []int64, at int64, t *types.Type) ([]int64, int6
                typ := t.Kind()
                switch typ {
                case types.TARRAY:
+                       te := t.Elem()
                        for i := int64(0); i < t.NumElem(); i++ {
-                               offsets, at = appendParamOffsets(offsets, at, t.Elem())
+                               at = align(at, te)
+                               offsets, at = appendParamOffsets(offsets, at, te)
                        }
                case types.TSTRUCT:
+                       at0 := at
                        for i, f := range t.Fields() {
+                               at = at0 + f.Offset // Fields may be over-aligned, see wasm32.
                                offsets, at = appendParamOffsets(offsets, at, f.Type)
                                if f.Type.Size() == 0 && i == t.NumFields()-1 {
                                        at++ // last field has zero width
@@ -668,12 +672,13 @@ func (pa *ABIParamAssignment) ComputePadding(storage []uint64) []uint64 {
        if len(types) != nr {
                panic("internal error")
        }
+       offsets, _ := appendParamOffsets([]int64{}, 0, pa.Type)
        off := int64(0)
        for idx, t := range types {
                ts := t.Size()
                off += int64(ts)
                if idx < len(types)-1 {
-                       noff := align(off, types[idx+1])
+                       noff := offsets[idx+1]
                        if noff != off {
                                padding[idx] = uint64(noff - off)
                        }

diff --git a/src/cmd/compile/internal/compare/compare_test.go b/src/cmd/compile/internal/compare/compare_test.go
index 2f761655094ff4560c723a1e9c3de040692c2ff3..4271effbdbb3d930a9df4e406c8b029fc9dddf13 100644 (file)
--- a/src/cmd/compile/internal/compare/compare_test.go
+++ b/src/cmd/compile/internal/compare/compare_test.go
@@ -23,8 +23,8 @@ func init() {
        types.PtrSize = 8
        types.RegSize = 8
        types.MaxWidth = 1 << 50
-       typecheck.InitUniverse()
        base.Ctxt = &obj.Link{Arch: &obj.LinkArch{Arch: &sys.Arch{Alignment: 1, CanMergeLoads: true}}}
+       typecheck.InitUniverse()
 }
 
 func TestEqStructCost(t *testing.T) {

diff --git a/src/cmd/compile/internal/devirtualize/pgo_test.go b/src/cmd/compile/internal/devirtualize/pgo_test.go
index cff4d63d51cc2ad42aedd8b9ca7035f5989ae1d1..6153b8c5ec7043e4812875858d6089a0765ca489 100644 (file)
--- a/src/cmd/compile/internal/devirtualize/pgo_test.go
+++ b/src/cmd/compile/internal/devirtualize/pgo_test.go
@@ -13,6 +13,7 @@ import (
        "cmd/internal/obj"
        "cmd/internal/pgo"
        "cmd/internal/src"
+       "cmd/internal/sys"
        "testing"
 )
 
@@ -23,8 +24,8 @@ func init() {
        types.PtrSize = 8
        types.RegSize = 8
        types.MaxWidth = 1 << 50
+       base.Ctxt = &obj.Link{Arch: &obj.LinkArch{Arch: &sys.Arch{Alignment: 1, CanMergeLoads: true}}}
        typecheck.InitUniverse()
-       base.Ctxt = &obj.Link{}
        base.Debug.PGODebug = 3
 }
 

diff --git a/src/cmd/compile/internal/inline/inlheur/texpr_classify_test.go b/src/cmd/compile/internal/inline/inlheur/texpr_classify_test.go
index 587eab03fcb954a95e1c576e8280be1e6fbc409b..b1cbb2bc0ec9d72c9d87fa26a00c030a986e3ba7 100644 (file)
--- a/src/cmd/compile/internal/inline/inlheur/texpr_classify_test.go
+++ b/src/cmd/compile/internal/inline/inlheur/texpr_classify_test.go
@@ -5,10 +5,13 @@
 package inlheur
 
 import (
+       "cmd/compile/internal/base"
        "cmd/compile/internal/ir"
        "cmd/compile/internal/typecheck"
        "cmd/compile/internal/types"
+       "cmd/internal/obj"
        "cmd/internal/src"
+       "cmd/internal/sys"
        "go/constant"
        "testing"
 )
@@ -21,6 +24,8 @@ func init() {
        types.PtrSize = 8
        types.RegSize = 8
        types.MaxWidth = 1 << 50
+       base.Ctxt = &obj.Link{Arch: &obj.LinkArch{Arch: &sys.Arch{Alignment: 1, CanMergeLoads: true}}}
+
        typecheck.InitUniverse()
        local = types.NewPkg("", "")
        fsym := &types.Sym{

diff --git a/src/cmd/compile/internal/ssa/export_test.go b/src/cmd/compile/internal/ssa/export_test.go
index b2c4b1997f2ba0bfd5d21a1ba1004f578a3d919e..c33c77f891cc53bf7950b7756afe53880785a199 100644 (file)
--- a/src/cmd/compile/internal/ssa/export_test.go
+++ b/src/cmd/compile/internal/ssa/export_test.go
@@ -7,6 +7,7 @@ package ssa
 import (
        "testing"
 
+       "cmd/compile/internal/base"
        "cmd/compile/internal/ir"
        "cmd/compile/internal/typecheck"
        "cmd/compile/internal/types"
@@ -15,6 +16,7 @@ import (
        "cmd/internal/obj/s390x"
        "cmd/internal/obj/x86"
        "cmd/internal/src"
+       "cmd/internal/sys"
 )
 
 var CheckFunc = checkFunc
@@ -115,6 +117,7 @@ func init() {
        types.RegSize = 8
        types.MaxWidth = 1 << 50
 
+       base.Ctxt = &obj.Link{Arch: &obj.LinkArch{Arch: &sys.Arch{Alignment: 1, CanMergeLoads: true}}}
        typecheck.InitUniverse()
        testTypes.SetTypPtrs()
 }

diff --git a/src/go/doc/comment/std.go b/src/go/doc/comment/std.go
index 35caa8b3191cead47803b980b5f9513b06d5b2ed..f6958512c22f3784d7dba4894fed4811ff9ff7f2 100644 (file)
--- a/src/go/doc/comment/std.go
+++ b/src/go/doc/comment/std.go
@@ -39,6 +39,7 @@ var stdPkgs = []string{
        "sort",
        "strconv",
        "strings",
+       "structs",
        "sync",
        "syscall",
        "testing",

diff --git a/src/structs/doc.go b/src/structs/doc.go
new file mode 100644 (file)
index 0000000..ec79490
--- /dev/null
+++ b/src/structs/doc.go
@@ -0,0 +1,10 @@
+// Copyright 2024 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 structs defines marker types that can be used as struct fields
+// to modify the properties of a struct.
+//
+// By convention, a marker type should be used as the type of a field
+// named "_", placed at the beginning of a struct type definition.
+package structs

diff --git a/src/structs/hostlayout.go b/src/structs/hostlayout.go
new file mode 100644 (file)
index 0000000..d373f24
--- /dev/null
+++ b/src/structs/hostlayout.go
@@ -0,0 +1,30 @@
+// Copyright 2024 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 structs
+
+// HostLayout marks a struct as using host memory layout. A struct with a
+// field of type HostLayout will be laid out in memory according to host
+// expectations, generally following the host's C ABI.
+//
+// HostLayout does not affect layout within any other struct-typed fields
+// of the containing struct, nor does it affect layout of structs
+// containing the struct marked as host layout.
+//
+// By convention, HostLayout should be used as the type of a field
+// named "_", placed at the beginning of the struct type definition.
+type HostLayout struct {
+       _ hostLayout // prevent accidental conversion with plain struct{}
+}
+
+// We use an unexported type within the exported type to give the marker
+// type itself, rather than merely its name, a recognizable identity in
+// the type system. The main consequence of this is that a user can give
+// the type a new name and it will still have the same properties, e.g.,
+//
+//     type HL structs.HostLayout
+//
+// It also prevents unintentional conversion of struct{} to a named marker type.
+type hostLayout struct {
+}