forked from golang/go
/
align.go
456 lines (387 loc) · 9.87 KB
/
align.go
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// Copyright 2009 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 gc
import (
"cmd/compile/internal/types"
"sort"
)
// sizeCalculationDisabled indicates whether it is safe
// to calculate Types' widths and alignments. See dowidth.
var sizeCalculationDisabled bool
// machine size and rounding alignment is dictated around
// the size of a pointer, set in betypeinit (see ../amd64/galign.go).
var defercalc int
func Rnd(o int64, r int64) int64 {
if r < 1 || r > 8 || r&(r-1) != 0 {
Fatalf("rnd %d", r)
}
return (o + r - 1) &^ (r - 1)
}
// expandiface computes the method set for interface type t by
// expanding embedded interfaces.
func expandiface(t *types.Type) {
var fields []*types.Field
for _, m := range t.Methods().Slice() {
if m.Sym != nil {
fields = append(fields, m)
checkwidth(m.Type)
continue
}
if !m.Type.IsInterface() {
yyerrorl(asNode(m.Nname).Pos, "interface contains embedded non-interface %v", m.Type)
m.SetBroke(true)
t.SetBroke(true)
// Add to fields so that error messages
// include the broken embedded type when
// printing t.
// TODO(mdempsky): Revisit this.
fields = append(fields, m)
continue
}
// Embedded interface: duplicate all methods
// (including broken ones, if any) and add to t's
// method set.
for _, t1 := range m.Type.Fields().Slice() {
f := types.NewField()
f.Type = t1.Type
f.SetBroke(t1.Broke())
f.Sym = t1.Sym
f.Nname = m.Nname // preserve embedding position
fields = append(fields, f)
}
}
sort.Sort(methcmp(fields))
// Access fields directly to avoid recursively calling dowidth
// within Type.Fields().
t.Extra.(*types.Interface).Fields.Set(fields)
}
func offmod(t *types.Type) {
o := int32(0)
for _, f := range t.Fields().Slice() {
f.Offset = int64(o)
o += int32(Widthptr)
if int64(o) >= thearch.MAXWIDTH {
yyerror("interface too large")
o = int32(Widthptr)
}
}
}
func widstruct(errtype *types.Type, t *types.Type, o int64, flag int) int64 {
starto := o
maxalign := int32(flag)
if maxalign < 1 {
maxalign = 1
}
lastzero := int64(0)
for _, f := range t.Fields().Slice() {
if f.Type == nil {
// broken field, just skip it so that other valid fields
// get a width.
continue
}
dowidth(f.Type)
if int32(f.Type.Align) > maxalign {
maxalign = int32(f.Type.Align)
}
if f.Type.Align > 0 {
o = Rnd(o, int64(f.Type.Align))
}
f.Offset = o
if asNode(f.Nname) != nil {
// addrescapes has similar code to update these offsets.
// Usually addrescapes runs after widstruct,
// in which case we could drop this,
// but function closure functions are the exception.
// NOTE(rsc): This comment may be stale.
// It's possible the ordering has changed and this is
// now the common case. I'm not sure.
if asNode(f.Nname).Name.Param.Stackcopy != nil {
asNode(f.Nname).Name.Param.Stackcopy.Xoffset = o
asNode(f.Nname).Xoffset = 0
} else {
asNode(f.Nname).Xoffset = o
}
}
w := f.Type.Width
if w < 0 {
Fatalf("invalid width %d", f.Type.Width)
}
if w == 0 {
lastzero = o
}
o += w
maxwidth := thearch.MAXWIDTH
// On 32-bit systems, reflect tables impose an additional constraint
// that each field start offset must fit in 31 bits.
if maxwidth < 1<<32 {
maxwidth = 1<<31 - 1
}
if o >= maxwidth {
yyerror("type %L too large", errtype)
o = 8 // small but nonzero
}
}
// For nonzero-sized structs which end in a zero-sized thing, we add
// an extra byte of padding to the type. This padding ensures that
// taking the address of the zero-sized thing can't manufacture a
// pointer to the next object in the heap. See issue 9401.
if flag == 1 && o > starto && o == lastzero {
o++
}
// final width is rounded
if flag != 0 {
o = Rnd(o, int64(maxalign))
}
t.Align = uint8(maxalign)
// type width only includes back to first field's offset
t.Width = o - starto
return o
}
// dowidth calculates and stores the size and alignment for t.
// If sizeCalculationDisabled is set, and the size/alignment
// have not already been calculated, it calls Fatal.
// This is used to prevent data races in the back end.
func dowidth(t *types.Type) {
if Widthptr == 0 {
Fatalf("dowidth without betypeinit")
}
if t == nil {
return
}
if t.Width == -2 {
if !t.Broke() {
t.SetBroke(true)
yyerrorl(asNode(t.Nod).Pos, "invalid recursive type %v", t)
}
t.Width = 0
return
}
if t.WidthCalculated() {
return
}
if sizeCalculationDisabled {
if t.Broke() {
// break infinite recursion from Fatal call below
return
}
t.SetBroke(true)
Fatalf("width not calculated: %v", t)
}
// break infinite recursion if the broken recursive type
// is referenced again
if t.Broke() && t.Width == 0 {
return
}
// defer checkwidth calls until after we're done
defercalc++
lno := lineno
if asNode(t.Nod) != nil {
lineno = asNode(t.Nod).Pos
}
t.Width = -2
t.Align = 0
et := t.Etype
switch et {
case TFUNC, TCHAN, TMAP, TSTRING:
break
// simtype == 0 during bootstrap
default:
if simtype[t.Etype] != 0 {
et = simtype[t.Etype]
}
}
w := int64(0)
switch et {
default:
Fatalf("dowidth: unknown type: %v", t)
// compiler-specific stuff
case TINT8, TUINT8, TBOOL:
// bool is int8
w = 1
case TINT16, TUINT16:
w = 2
case TINT32, TUINT32, TFLOAT32:
w = 4
case TINT64, TUINT64, TFLOAT64:
w = 8
t.Align = uint8(Widthreg)
case TCOMPLEX64:
w = 8
t.Align = 4
case TCOMPLEX128:
w = 16
t.Align = uint8(Widthreg)
case TPTR32:
w = 4
checkwidth(t.Elem())
case TPTR64:
w = 8
checkwidth(t.Elem())
case TUNSAFEPTR:
w = int64(Widthptr)
case TINTER: // implemented as 2 pointers
w = 2 * int64(Widthptr)
t.Align = uint8(Widthptr)
expandiface(t)
case TCHAN: // implemented as pointer
w = int64(Widthptr)
checkwidth(t.Elem())
// make fake type to check later to
// trigger channel argument check.
t1 := types.NewChanArgs(t)
checkwidth(t1)
case TCHANARGS:
t1 := t.ChanArgs()
dowidth(t1) // just in case
if t1.Elem().Width >= 1<<16 {
yyerror("channel element type too large (>64kB)")
}
w = 1 // anything will do
case TMAP: // implemented as pointer
w = int64(Widthptr)
checkwidth(t.Val())
checkwidth(t.Key())
case TFORW: // should have been filled in
if !t.Broke() {
yyerror("invalid recursive type %v", t)
}
w = 1 // anything will do
case TANY:
// dummy type; should be replaced before use.
Fatalf("dowidth any")
case TSTRING:
if sizeof_String == 0 {
Fatalf("early dowidth string")
}
w = int64(sizeof_String)
t.Align = uint8(Widthptr)
case TARRAY:
if t.Elem() == nil {
break
}
if t.IsDDDArray() {
if !t.Broke() {
yyerror("use of [...] array outside of array literal")
t.SetBroke(true)
}
break
}
dowidth(t.Elem())
if t.Elem().Width != 0 {
cap := (uint64(thearch.MAXWIDTH) - 1) / uint64(t.Elem().Width)
if uint64(t.NumElem()) > cap {
yyerror("type %L larger than address space", t)
}
}
w = t.NumElem() * t.Elem().Width
t.Align = t.Elem().Align
case TSLICE:
if t.Elem() == nil {
break
}
w = int64(sizeof_Array)
checkwidth(t.Elem())
t.Align = uint8(Widthptr)
case TSTRUCT:
if t.IsFuncArgStruct() {
Fatalf("dowidth fn struct %v", t)
}
w = widstruct(t, t, 0, 1)
// make fake type to check later to
// trigger function argument computation.
case TFUNC:
t1 := types.NewFuncArgs(t)
checkwidth(t1)
w = int64(Widthptr) // width of func type is pointer
// function is 3 cated structures;
// compute their widths as side-effect.
case TFUNCARGS:
t1 := t.FuncArgs()
w = widstruct(t1, t1.Recvs(), 0, 0)
w = widstruct(t1, t1.Params(), w, Widthreg)
w = widstruct(t1, t1.Results(), w, Widthreg)
t1.Extra.(*types.Func).Argwid = w
if w%int64(Widthreg) != 0 {
Warn("bad type %v %d\n", t1, w)
}
t.Align = 1
}
if Widthptr == 4 && w != int64(int32(w)) {
yyerror("type %v too large", t)
}
t.Width = w
if t.Align == 0 {
if w > 8 || w&(w-1) != 0 || w == 0 {
Fatalf("invalid alignment for %v", t)
}
t.Align = uint8(w)
}
if t.Etype == TINTER {
// We defer calling these functions until after
// setting t.Width and t.Align so the recursive calls
// to dowidth within t.Fields() will succeed.
checkdupfields("method", t)
offmod(t)
}
lineno = lno
if defercalc == 1 {
resumecheckwidth()
} else {
defercalc--
}
}
// when a type's width should be known, we call checkwidth
// to compute it. during a declaration like
//
// type T *struct { next T }
//
// it is necessary to defer the calculation of the struct width
// until after T has been initialized to be a pointer to that struct.
// similarly, during import processing structs may be used
// before their definition. in those situations, calling
// defercheckwidth() stops width calculations until
// resumecheckwidth() is called, at which point all the
// checkwidths that were deferred are executed.
// dowidth should only be called when the type's size
// is needed immediately. checkwidth makes sure the
// size is evaluated eventually.
var deferredTypeStack []*types.Type
func checkwidth(t *types.Type) {
if t == nil {
return
}
// function arg structs should not be checked
// outside of the enclosing function.
if t.IsFuncArgStruct() {
Fatalf("checkwidth %v", t)
}
if defercalc == 0 {
dowidth(t)
return
}
if t.Deferwidth() {
return
}
t.SetDeferwidth(true)
deferredTypeStack = append(deferredTypeStack, t)
}
func defercheckwidth() {
// we get out of sync on syntax errors, so don't be pedantic.
if defercalc != 0 && nerrors == 0 {
Fatalf("defercheckwidth")
}
defercalc = 1
}
func resumecheckwidth() {
if defercalc == 0 {
Fatalf("resumecheckwidth")
}
for len(deferredTypeStack) > 0 {
t := deferredTypeStack[len(deferredTypeStack)-1]
deferredTypeStack = deferredTypeStack[:len(deferredTypeStack)-1]
t.SetDeferwidth(false)
dowidth(t)
}
defercalc = 0
}