size.go

Documentation: cmd/compile/internal/types

     1  // Copyright 2009 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  package types
     6  
     7  import (
     8  	"math"
     9  	"sort"
    10  
    11  	"cmd/compile/internal/base"
    12  	"cmd/internal/src"
    13  	"internal/types/errors"
    14  )
    15  
    16  var PtrSize int
    17  
    18  var RegSize int
    19  
    20  // Slices in the runtime are represented by three components:
    21  //
    22  //	type slice struct {
    23  //		ptr unsafe.Pointer
    24  //		len int
    25  //		cap int
    26  //	}
    27  //
    28  // Strings in the runtime are represented by two components:
    29  //
    30  //	type string struct {
    31  //		ptr unsafe.Pointer
    32  //		len int
    33  //	}
    34  //
    35  // These variables are the offsets of fields and sizes of these structs.
    36  var (
    37  	SlicePtrOffset int64
    38  	SliceLenOffset int64
    39  	SliceCapOffset int64
    40  
    41  	SliceSize  int64
    42  	StringSize int64
    43  )
    44  
    45  var SkipSizeForTracing bool
    46  
    47  // typePos returns the position associated with t.
    48  // This is where t was declared or where it appeared as a type expression.
    49  func typePos(t *Type) src.XPos {
    50  	if pos := t.Pos(); pos.IsKnown() {
    51  		return pos
    52  	}
    53  	base.Fatalf("bad type: %v", t)
    54  	panic("unreachable")
    55  }
    56  
    57  // MaxWidth is the maximum size of a value on the target architecture.
    58  var MaxWidth int64
    59  
    60  // CalcSizeDisabled indicates whether it is safe
    61  // to calculate Types' widths and alignments. See CalcSize.
    62  var CalcSizeDisabled bool
    63  
    64  // machine size and rounding alignment is dictated around
    65  // the size of a pointer, set in gc.Main (see ../gc/main.go).
    66  var defercalc int
    67  
    68  // RoundUp rounds o to a multiple of r, r is a power of 2.
    69  func RoundUp(o int64, r int64) int64 {
    70  	if r < 1 || r > 8 || r&(r-1) != 0 {
    71  		base.Fatalf("Round %d", r)
    72  	}
    73  	return (o + r - 1) &^ (r - 1)
    74  }
    75  
    76  // expandiface computes the method set for interface type t by
    77  // expanding embedded interfaces.
    78  func expandiface(t *Type) {
    79  	seen := make(map[*Sym]*Field)
    80  	var methods []*Field
    81  
    82  	addMethod := func(m *Field, explicit bool) {
    83  		switch prev := seen[m.Sym]; {
    84  		case prev == nil:
    85  			seen[m.Sym] = m
    86  		case !explicit && Identical(m.Type, prev.Type):
    87  			return
    88  		default:
    89  			base.ErrorfAt(m.Pos, errors.DuplicateDecl, "duplicate method %s", m.Sym.Name)
    90  		}
    91  		methods = append(methods, m)
    92  	}
    93  
    94  	{
    95  		methods := t.Methods()
    96  		sort.SliceStable(methods, func(i, j int) bool {
    97  			mi, mj := methods[i], methods[j]
    98  
    99  			// Sort embedded types by type name (if any).
   100  			if mi.Sym == nil && mj.Sym == nil {
   101  				return mi.Type.Sym().Less(mj.Type.Sym())
   102  			}
   103  
   104  			// Sort methods before embedded types.
   105  			if mi.Sym == nil || mj.Sym == nil {
   106  				return mi.Sym != nil
   107  			}
   108  
   109  			// Sort methods by symbol name.
   110  			return mi.Sym.Less(mj.Sym)
   111  		})
   112  	}
   113  
   114  	for _, m := range t.Methods() {
   115  		if m.Sym == nil {
   116  			continue
   117  		}
   118  
   119  		CheckSize(m.Type)
   120  		addMethod(m, true)
   121  	}
   122  
   123  	for _, m := range t.Methods() {
   124  		if m.Sym != nil || m.Type == nil {
   125  			continue
   126  		}
   127  
   128  		// In 1.18, embedded types can be anything. In Go 1.17, we disallow
   129  		// embedding anything other than interfaces. This requirement was caught
   130  		// by types2 already, so allow non-interface here.
   131  		if !m.Type.IsInterface() {
   132  			continue
   133  		}
   134  
   135  		// Embedded interface: duplicate all methods
   136  		// and add to t's method set.
   137  		for _, t1 := range m.Type.AllMethods() {
   138  			f := NewField(m.Pos, t1.Sym, t1.Type)
   139  			addMethod(f, false)
   140  
   141  			// Clear position after typechecking, for consistency with types2.
   142  			f.Pos = src.NoXPos
   143  		}
   144  
   145  		// Clear position after typechecking, for consistency with types2.
   146  		m.Pos = src.NoXPos
   147  	}
   148  
   149  	sort.Sort(MethodsByName(methods))
   150  
   151  	if int64(len(methods)) >= MaxWidth/int64(PtrSize) {
   152  		base.ErrorfAt(typePos(t), 0, "interface too large")
   153  	}
   154  	for i, m := range methods {
   155  		m.Offset = int64(i) * int64(PtrSize)
   156  	}
   157  
   158  	t.SetAllMethods(methods)
   159  }
   160  
   161  // calcStructOffset computes the offsets of a sequence of fields,
   162  // starting at the given offset. It returns the resulting offset and
   163  // maximum field alignment.
   164  func calcStructOffset(t *Type, fields []*Field, offset int64) int64 {
   165  	for _, f := range fields {
   166  		CalcSize(f.Type)
   167  		offset = RoundUp(offset, int64(f.Type.align))
   168  
   169  		if t.IsStruct() { // param offsets depend on ABI
   170  			f.Offset = offset
   171  
   172  			// If type T contains a field F marked as not-in-heap,
   173  			// then T must also be a not-in-heap type. Otherwise,
   174  			// you could heap allocate T and then get a pointer F,
   175  			// which would be a heap pointer to a not-in-heap type.
   176  			if f.Type.NotInHeap() {
   177  				t.SetNotInHeap(true)
   178  			}
   179  		}
   180  
   181  		offset += f.Type.width
   182  
   183  		maxwidth := MaxWidth
   184  		// On 32-bit systems, reflect tables impose an additional constraint
   185  		// that each field start offset must fit in 31 bits.
   186  		if maxwidth < 1<<32 {
   187  			maxwidth = 1<<31 - 1
   188  		}
   189  		if offset >= maxwidth {
   190  			base.ErrorfAt(typePos(t), 0, "type %L too large", t)
   191  			offset = 8 // small but nonzero
   192  		}
   193  	}
   194  
   195  	return offset
   196  }
   197  
   198  func isAtomicStdPkg(p *Pkg) bool {
   199  	if p.Prefix == `""` {
   200  		panic("bad package prefix")
   201  	}
   202  	return p.Prefix == "sync/atomic" || p.Prefix == "internal/runtime/atomic"
   203  }
   204  
   205  // CalcSize calculates and stores the size, alignment, eq/hash algorithm,
   206  // and ptrBytes for t.
   207  // If CalcSizeDisabled is set, and the size/alignment
   208  // have not already been calculated, it calls Fatal.
   209  // This is used to prevent data races in the back end.
   210  func CalcSize(t *Type) {
   211  	// Calling CalcSize when typecheck tracing enabled is not safe.
   212  	// See issue #33658.
   213  	if base.EnableTrace && SkipSizeForTracing {
   214  		return
   215  	}
   216  	if PtrSize == 0 {
   217  		// Assume this is a test.
   218  		return
   219  	}
   220  
   221  	if t == nil {
   222  		return
   223  	}
   224  
   225  	if t.width == -2 {
   226  		t.width = 0
   227  		t.align = 1
   228  		base.Fatalf("invalid recursive type %v", t)
   229  		return
   230  	}
   231  
   232  	if t.widthCalculated() {
   233  		return
   234  	}
   235  
   236  	if CalcSizeDisabled {
   237  		base.Fatalf("width not calculated: %v", t)
   238  	}
   239  
   240  	// defer CheckSize calls until after we're done
   241  	DeferCheckSize()
   242  
   243  	lno := base.Pos
   244  	if pos := t.Pos(); pos.IsKnown() {
   245  		base.Pos = pos
   246  	}
   247  
   248  	t.width = -2
   249  	t.align = 0  // 0 means use t.Width, below
   250  	t.alg = AMEM // default
   251  	// default t.ptrBytes is 0.
   252  	if t.Noalg() {
   253  		t.setAlg(ANOALG)
   254  	}
   255  
   256  	et := t.Kind()
   257  	switch et {
   258  	case TFUNC, TCHAN, TMAP, TSTRING:
   259  		break
   260  
   261  	// SimType == 0 during bootstrap
   262  	default:
   263  		if SimType[t.Kind()] != 0 {
   264  			et = SimType[t.Kind()]
   265  		}
   266  	}
   267  
   268  	var w int64
   269  	switch et {
   270  	default:
   271  		base.Fatalf("CalcSize: unknown type: %v", t)
   272  
   273  	// compiler-specific stuff
   274  	case TINT8, TUINT8, TBOOL:
   275  		// bool is int8
   276  		w = 1
   277  		t.intRegs = 1
   278  
   279  	case TINT16, TUINT16:
   280  		w = 2
   281  		t.intRegs = 1
   282  
   283  	case TINT32, TUINT32:
   284  		w = 4
   285  		t.intRegs = 1
   286  
   287  	case TINT64, TUINT64:
   288  		w = 8
   289  		t.align = uint8(RegSize)
   290  		t.intRegs = uint8(8 / RegSize)
   291  
   292  	case TFLOAT32:
   293  		w = 4
   294  		t.floatRegs = 1
   295  		t.setAlg(AFLOAT32)
   296  
   297  	case TFLOAT64:
   298  		w = 8
   299  		t.align = uint8(RegSize)
   300  		t.floatRegs = 1
   301  		t.setAlg(AFLOAT64)
   302  
   303  	case TCOMPLEX64:
   304  		w = 8
   305  		t.align = 4
   306  		t.floatRegs = 2
   307  		t.setAlg(ACPLX64)
   308  
   309  	case TCOMPLEX128:
   310  		w = 16
   311  		t.align = uint8(RegSize)
   312  		t.floatRegs = 2
   313  		t.setAlg(ACPLX128)
   314  
   315  	case TPTR:
   316  		w = int64(PtrSize)
   317  		t.intRegs = 1
   318  		CheckSize(t.Elem())
   319  		t.ptrBytes = int64(PtrSize) // See PtrDataSize
   320  
   321  	case TUNSAFEPTR:
   322  		w = int64(PtrSize)
   323  		t.intRegs = 1
   324  		t.ptrBytes = int64(PtrSize)
   325  
   326  	case TINTER: // implemented as 2 pointers
   327  		w = 2 * int64(PtrSize)
   328  		t.align = uint8(PtrSize)
   329  		t.intRegs = 2
   330  		expandiface(t)
   331  		if len(t.allMethods.Slice()) == 0 {
   332  			t.setAlg(ANILINTER)
   333  		} else {
   334  			t.setAlg(AINTER)
   335  		}
   336  		t.ptrBytes = int64(2 * PtrSize)
   337  
   338  	case TCHAN: // implemented as pointer
   339  		w = int64(PtrSize)
   340  		t.intRegs = 1
   341  		t.ptrBytes = int64(PtrSize)
   342  
   343  		CheckSize(t.Elem())
   344  
   345  		// Make fake type to trigger channel element size check after
   346  		// any top-level recursive type has been completed.
   347  		t1 := NewChanArgs(t)
   348  		CheckSize(t1)
   349  
   350  	case TCHANARGS:
   351  		t1 := t.ChanArgs()
   352  		CalcSize(t1) // just in case
   353  		// Make sure size of t1.Elem() is calculated at this point. We can
   354  		// use CalcSize() here rather than CheckSize(), because the top-level
   355  		// (possibly recursive) type will have been calculated before the fake
   356  		// chanargs is handled.
   357  		CalcSize(t1.Elem())
   358  		if t1.Elem().width >= 1<<16 {
   359  			base.Errorf("channel element type too large (>64kB)")
   360  		}
   361  		w = 1 // anything will do
   362  
   363  	case TMAP: // implemented as pointer
   364  		w = int64(PtrSize)
   365  		t.intRegs = 1
   366  		CheckSize(t.Elem())
   367  		CheckSize(t.Key())
   368  		t.setAlg(ANOEQ)
   369  		t.ptrBytes = int64(PtrSize)
   370  
   371  	case TFORW: // should have been filled in
   372  		base.Fatalf("invalid recursive type %v", t)
   373  
   374  	case TANY: // not a real type; should be replaced before use.
   375  		base.Fatalf("CalcSize any")
   376  
   377  	case TSTRING:
   378  		if StringSize == 0 {
   379  			base.Fatalf("early CalcSize string")
   380  		}
   381  		w = StringSize
   382  		t.align = uint8(PtrSize)
   383  		t.intRegs = 2
   384  		t.setAlg(ASTRING)
   385  		t.ptrBytes = int64(PtrSize)
   386  
   387  	case TARRAY:
   388  		if t.Elem() == nil {
   389  			break
   390  		}
   391  
   392  		CalcSize(t.Elem())
   393  		t.SetNotInHeap(t.Elem().NotInHeap())
   394  		if t.Elem().width != 0 {
   395  			cap := (uint64(MaxWidth) - 1) / uint64(t.Elem().width)
   396  			if uint64(t.NumElem()) > cap {
   397  				base.Errorf("type %L larger than address space", t)
   398  			}
   399  		}
   400  		w = t.NumElem() * t.Elem().width
   401  		t.align = t.Elem().align
   402  
   403  		// ABIInternal only allows "trivial" arrays (i.e., length 0 or 1)
   404  		// to be passed by register.
   405  		switch t.NumElem() {
   406  		case 0:
   407  			t.intRegs = 0
   408  			t.floatRegs = 0
   409  		case 1:
   410  			t.intRegs = t.Elem().intRegs
   411  			t.floatRegs = t.Elem().floatRegs
   412  		default:
   413  			t.intRegs = math.MaxUint8
   414  			t.floatRegs = math.MaxUint8
   415  		}
   416  		switch a := t.Elem().alg; a {
   417  		case AMEM, ANOEQ, ANOALG:
   418  			t.setAlg(a)
   419  		default:
   420  			switch t.NumElem() {
   421  			case 0:
   422  				// We checked above that the element type is comparable.
   423  				t.setAlg(AMEM)
   424  			case 1:
   425  				// Single-element array is same as its lone element.
   426  				t.setAlg(a)
   427  			default:
   428  				t.setAlg(ASPECIAL)
   429  			}
   430  		}
   431  		if t.NumElem() > 0 {
   432  			x := PtrDataSize(t.Elem())
   433  			if x > 0 {
   434  				t.ptrBytes = t.Elem().width*(t.NumElem()-1) + x
   435  			}
   436  		}
   437  
   438  	case TSLICE:
   439  		if t.Elem() == nil {
   440  			break
   441  		}
   442  		w = SliceSize
   443  		CheckSize(t.Elem())
   444  		t.align = uint8(PtrSize)
   445  		t.intRegs = 3
   446  		t.setAlg(ANOEQ)
   447  		if !t.Elem().NotInHeap() {
   448  			t.ptrBytes = int64(PtrSize)
   449  		}
   450  
   451  	case TSTRUCT:
   452  		if t.IsFuncArgStruct() {
   453  			base.Fatalf("CalcSize fn struct %v", t)
   454  		}
   455  		CalcStructSize(t)
   456  		w = t.width
   457  
   458  	// make fake type to check later to
   459  	// trigger function argument computation.
   460  	case TFUNC:
   461  		t1 := NewFuncArgs(t)
   462  		CheckSize(t1)
   463  		w = int64(PtrSize) // width of func type is pointer
   464  		t.intRegs = 1
   465  		t.setAlg(ANOEQ)
   466  		t.ptrBytes = int64(PtrSize)
   467  
   468  	// function is 3 cated structures;
   469  	// compute their widths as side-effect.
   470  	case TFUNCARGS:
   471  		t1 := t.FuncArgs()
   472  		// TODO(mdempsky): Should package abi be responsible for computing argwid?
   473  		w = calcStructOffset(t1, t1.Recvs(), 0)
   474  		w = calcStructOffset(t1, t1.Params(), w)
   475  		w = RoundUp(w, int64(RegSize))
   476  		w = calcStructOffset(t1, t1.Results(), w)
   477  		w = RoundUp(w, int64(RegSize))
   478  		t1.extra.(*Func).Argwid = w
   479  		t.align = 1
   480  	}
   481  
   482  	if PtrSize == 4 && w != int64(int32(w)) {
   483  		base.Errorf("type %v too large", t)
   484  	}
   485  
   486  	t.width = w
   487  	if t.align == 0 {
   488  		if w == 0 || w > 8 || w&(w-1) != 0 {
   489  			base.Fatalf("invalid alignment for %v", t)
   490  		}
   491  		t.align = uint8(w)
   492  	}
   493  
   494  	base.Pos = lno
   495  
   496  	ResumeCheckSize()
   497  }
   498  
   499  // CalcStructSize calculates the size of t,
   500  // filling in t.width, t.align, t.intRegs, and t.floatRegs,
   501  // even if size calculation is otherwise disabled.
   502  func CalcStructSize(t *Type) {
   503  	var maxAlign uint8 = 1
   504  
   505  	// Recognize special types. This logic is duplicated in go/types and
   506  	// cmd/compile/internal/types2.
   507  	if sym := t.Sym(); sym != nil {
   508  		switch {
   509  		case sym.Name == "align64" && isAtomicStdPkg(sym.Pkg):
   510  			maxAlign = 8
   511  		}
   512  	}
   513  
   514  	fields := t.Fields()
   515  	size := calcStructOffset(t, fields, 0)
   516  
   517  	// For non-zero-sized structs which end in a zero-sized field, we
   518  	// add an extra byte of padding to the type. This padding ensures
   519  	// that taking the address of a zero-sized field can't manufacture a
   520  	// pointer to the next object in the heap. See issue 9401.
   521  	if size > 0 && fields[len(fields)-1].Type.width == 0 {
   522  		size++
   523  	}
   524  
   525  	var intRegs, floatRegs uint64
   526  	for _, field := range fields {
   527  		typ := field.Type
   528  
   529  		// The alignment of a struct type is the maximum alignment of its
   530  		// field types.
   531  		if align := typ.align; align > maxAlign {
   532  			maxAlign = align
   533  		}
   534  
   535  		// Each field needs its own registers.
   536  		// We sum in uint64 to avoid possible overflows.
   537  		intRegs += uint64(typ.intRegs)
   538  		floatRegs += uint64(typ.floatRegs)
   539  	}
   540  
   541  	// Final size includes trailing padding.
   542  	size = RoundUp(size, int64(maxAlign))
   543  
   544  	if intRegs > math.MaxUint8 || floatRegs > math.MaxUint8 {
   545  		intRegs = math.MaxUint8
   546  		floatRegs = math.MaxUint8
   547  	}
   548  
   549  	t.width = size
   550  	t.align = maxAlign
   551  	t.intRegs = uint8(intRegs)
   552  	t.floatRegs = uint8(floatRegs)
   553  
   554  	// Compute eq/hash algorithm type.
   555  	t.alg = AMEM // default
   556  	if t.Noalg() {
   557  		t.setAlg(ANOALG)
   558  	}
   559  	if len(fields) == 1 && !fields[0].Sym.IsBlank() {
   560  		// One-field struct is same as that one field alone.
   561  		t.setAlg(fields[0].Type.alg)
   562  	} else {
   563  		for i, f := range fields {
   564  			a := f.Type.alg
   565  			switch a {
   566  			case ANOEQ, ANOALG:
   567  			case AMEM:
   568  				// Blank fields and padded fields need a special compare.
   569  				if f.Sym.IsBlank() || IsPaddedField(t, i) {
   570  					a = ASPECIAL
   571  				}
   572  			default:
   573  				// Fields with non-memory equality need a special compare.
   574  				a = ASPECIAL
   575  			}
   576  			t.setAlg(a)
   577  		}
   578  	}
   579  	// Compute ptrBytes.
   580  	for i := len(fields) - 1; i >= 0; i-- {
   581  		f := fields[i]
   582  		if size := PtrDataSize(f.Type); size > 0 {
   583  			t.ptrBytes = f.Offset + size
   584  			break
   585  		}
   586  	}
   587  }
   588  
   589  func (t *Type) widthCalculated() bool {
   590  	return t.align > 0
   591  }
   592  
   593  // when a type's width should be known, we call CheckSize
   594  // to compute it.  during a declaration like
   595  //
   596  //	type T *struct { next T }
   597  //
   598  // it is necessary to defer the calculation of the struct width
   599  // until after T has been initialized to be a pointer to that struct.
   600  // similarly, during import processing structs may be used
   601  // before their definition.  in those situations, calling
   602  // DeferCheckSize() stops width calculations until
   603  // ResumeCheckSize() is called, at which point all the
   604  // CalcSizes that were deferred are executed.
   605  // CalcSize should only be called when the type's size
   606  // is needed immediately.  CheckSize makes sure the
   607  // size is evaluated eventually.
   608  
   609  var deferredTypeStack []*Type
   610  
   611  func CheckSize(t *Type) {
   612  	if t == nil {
   613  		return
   614  	}
   615  
   616  	// function arg structs should not be checked
   617  	// outside of the enclosing function.
   618  	if t.IsFuncArgStruct() {
   619  		base.Fatalf("CheckSize %v", t)
   620  	}
   621  
   622  	if defercalc == 0 {
   623  		CalcSize(t)
   624  		return
   625  	}
   626  
   627  	// if type has not yet been pushed on deferredTypeStack yet, do it now
   628  	if !t.Deferwidth() {
   629  		t.SetDeferwidth(true)
   630  		deferredTypeStack = append(deferredTypeStack, t)
   631  	}
   632  }
   633  
   634  func DeferCheckSize() {
   635  	defercalc++
   636  }
   637  
   638  func ResumeCheckSize() {
   639  	if defercalc == 1 {
   640  		for len(deferredTypeStack) > 0 {
   641  			t := deferredTypeStack[len(deferredTypeStack)-1]
   642  			deferredTypeStack = deferredTypeStack[:len(deferredTypeStack)-1]
   643  			t.SetDeferwidth(false)
   644  			CalcSize(t)
   645  		}
   646  	}
   647  
   648  	defercalc--
   649  }
   650  
   651  // PtrDataSize returns the length in bytes of the prefix of t
   652  // containing pointer data. Anything after this offset is scalar data.
   653  //
   654  // PtrDataSize is only defined for actual Go types. It's an error to
   655  // use it on compiler-internal types (e.g., TSSA, TRESULTS).
   656  func PtrDataSize(t *Type) int64 {
   657  	CalcSize(t)
   658  	x := t.ptrBytes
   659  	if t.Kind() == TPTR && t.Elem().NotInHeap() {
   660  		// Note: this is done here instead of when we're setting
   661  		// the ptrBytes field, because at that time (in NewPtr, usually)
   662  		// the NotInHeap bit of the element type might not be set yet.
   663  		x = 0
   664  	}
   665  	return x
   666  }
   667
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