cmd/internal/obj: add Align field to LSym

This will permit the compiler and assembler to specify the alignment
of symbols that they create.

Careful placement of the new field, plus rearranging an existing field,
means that LSym does not change size (as tested by TestSizeof).
The new alignment field is int16, permitting alignment up to 16384,
more than we ever need in practice. If necessary we could change the
field to uint8 and store the alignment as a power of two,
as is done in the linker.

This replaces the Align field in FuncInfo.

For #6853
For #36313

Change-Id: I421e8238ab57958fea8e4eab0649ce5288e7f92f
Reviewed-on: https://go-review.googlesource.com/c/go/+/727020
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Keith Randall <khr@golang.org>
Auto-Submit: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Cherry Mui <cherryyz@google.com>
Reviewed-by: Keith Randall <khr@google.com>

6 files changed, 15 insertions, 18 deletions

diff --git a/src/cmd/internal/obj/link.go b/src/cmd/internal/obj/link.go
index 05ffba11ea..088a7c57aa 100644
--- a/src/cmd/internal/obj/link.go
+++ b/src/cmd/internal/obj/link.go
@@ -456,9 +456,10 @@ const (
 // It represents Go symbols in a flat pkg+"."+name namespace.
 type LSym struct {
 	Name string
-	Type objabi.SymKind
 	Attribute
+	Type objabi.SymKind
 
+	Align  int16
 	Size   int64
 	Gotype *LSym
 	P      []byte
@@ -475,7 +476,6 @@ type LSym struct {
 type FuncInfo struct {
 	Args      int32
 	Locals    int32
-	Align     int32
 	FuncID    abi.FuncID
 	FuncFlag  abi.FuncFlag
 	StartLine int32
diff --git a/src/cmd/internal/obj/loong64/asm.go b/src/cmd/internal/obj/loong64/asm.go
index f992518015..2cf608fb84 100644
--- a/src/cmd/internal/obj/loong64/asm.go
+++ b/src/cmd/internal/obj/loong64/asm.go
@@ -549,8 +549,8 @@ func span0(ctxt *obj.Link, cursym *obj.LSym, newprog obj.ProgAlloc) {
 				alignedValue := p.From.Offset
 				m = pcAlignPadLength(ctxt, pc, alignedValue)
 				// Update the current text symbol alignment value.
-				if int32(alignedValue) > cursym.Func().Align {
-					cursym.Func().Align = int32(alignedValue)
+				if int16(alignedValue) > cursym.Align {
+					cursym.Align = int16(alignedValue)
 				}
 				break
 			case obj.ANOP, obj.AFUNCDATA, obj.APCDATA:
diff --git a/src/cmd/internal/obj/objfile.go b/src/cmd/internal/obj/objfile.go
index 4401f1bb74..53691ccb6c 100644
--- a/src/cmd/internal/obj/objfile.go
+++ b/src/cmd/internal/obj/objfile.go
@@ -369,11 +369,8 @@ func (w *writer) Sym(s *LSym) {
 	if strings.HasPrefix(name, "gofile..") {
 		name = filepath.ToSlash(name)
 	}
-	var align uint32
-	if fn := s.Func(); fn != nil {
-		align = uint32(fn.Align)
-	}
-	if s.ContentAddressable() && s.Size != 0 {
+	align := uint32(s.Align)
+	if s.ContentAddressable() && s.Size != 0 && align == 0 {
 		// We generally assume data symbols are naturally aligned
 		// (e.g. integer constants), except for strings and a few
 		// compiler-emitted funcdata. If we dedup a string symbol and
@@ -895,10 +892,10 @@ func (ctxt *Link) writeSymDebugNamed(s *LSym, name string) {
 	if s.Func() != nil && s.Func().FuncFlag&abi.FuncFlagAsm != 0 {
 		fmt.Fprintf(ctxt.Bso, "asm ")
 	}
-	fmt.Fprintf(ctxt.Bso, "size=%d", s.Size)
+	fmt.Fprintf(ctxt.Bso, "size=%d align=%#x", s.Size, s.Align)
 	if s.Type.IsText() {
 		fn := s.Func()
-		fmt.Fprintf(ctxt.Bso, " args=%#x locals=%#x funcid=%#x align=%#x", uint64(fn.Args), uint64(fn.Locals), uint64(fn.FuncID), uint64(fn.Align))
+		fmt.Fprintf(ctxt.Bso, " args=%#x locals=%#x funcid=%#x", uint64(fn.Args), uint64(fn.Locals), uint64(fn.FuncID))
 		if s.Leaf() {
 			fmt.Fprintf(ctxt.Bso, " leaf")
 		}
diff --git a/src/cmd/internal/obj/ppc64/asm9.go b/src/cmd/internal/obj/ppc64/asm9.go
index a39c206c22..06ad72eed8 100644
--- a/src/cmd/internal/obj/ppc64/asm9.go
+++ b/src/cmd/internal/obj/ppc64/asm9.go
@@ -595,8 +595,8 @@ func addpad(pc, a int64, ctxt *obj.Link, cursym *obj.LSym) int {
 		// requested then the function alignment must also be promoted.
 		// The function alignment is not promoted on AIX at this time.
 		// TODO: Investigate AIX function alignment.
-		if ctxt.Headtype != objabi.Haix && cursym.Func().Align < int32(a) {
-			cursym.Func().Align = int32(a)
+		if ctxt.Headtype != objabi.Haix && cursym.Align < int16(a) {
+			cursym.Align = int16(a)
 		}
 		if pc&(a-1) != 0 {
 			return int(a - (pc & (a - 1)))
@@ -796,7 +796,7 @@ func span9(ctxt *obj.Link, cursym *obj.LSym, newprog obj.ProgAlloc) {
 	}
 
 	c.cursym.Size = pc
-	c.cursym.Func().Align = falign
+	c.cursym.Align = int16(falign)
 	c.cursym.Grow(c.cursym.Size)
 
 	// lay out the code, emitting code and data relocations.
diff --git a/src/cmd/internal/obj/riscv/obj.go b/src/cmd/internal/obj/riscv/obj.go
index 043be17c07..24e0a454cd 100644
--- a/src/cmd/internal/obj/riscv/obj.go
+++ b/src/cmd/internal/obj/riscv/obj.go
@@ -793,8 +793,8 @@ func preprocess(ctxt *obj.Link, cursym *obj.LSym, newprog obj.ProgAlloc) {
 				ctxt.Diag("alignment value of an instruction must be a power of two and in the range [4, 2048], got %d\n", alignedValue)
 			}
 			// Update the current text symbol alignment value.
-			if int32(alignedValue) > cursym.Func().Align {
-				cursym.Func().Align = int32(alignedValue)
+			if int16(alignedValue) > cursym.Align {
+				cursym.Align = int16(alignedValue)
 			}
 		}
 	}
diff --git a/src/cmd/internal/obj/util.go b/src/cmd/internal/obj/util.go
index 7d87bff949..86ba4deb73 100644
--- a/src/cmd/internal/obj/util.go
+++ b/src/cmd/internal/obj/util.go
@@ -737,7 +737,7 @@ func AlignmentPaddingLength(pc int32, p *Prog, ctxt *Link) int {
 // the required code alignment
 func requireAlignment(a int64, ctxt *Link, cursym *LSym) {
 	// TODO remove explicit knowledge about AIX.
-	if ctxt.Headtype != objabi.Haix && cursym.Func().Align < int32(a) {
-		cursym.Func().Align = int32(a)
+	if ctxt.Headtype != objabi.Haix && cursym.Align < int16(a) {
+		cursym.Align = int16(a)
 	}
 }