sizes.go

Documentation: go/types

     1  // Code generated by "go test -run=Generate -write=all"; DO NOT EDIT.
     2  
     3  // Copyright 2013 The Go Authors. All rights reserved.
     4  // Use of this source code is governed by a BSD-style
     5  // license that can be found in the LICENSE file.
     6  
     7  // This file implements Sizes.
     8  
     9  package types
    10  
    11  // Sizes defines the sizing functions for package unsafe.
    12  type Sizes interface {
    13  	// Alignof returns the alignment of a variable of type T.
    14  	// Alignof must implement the alignment guarantees required by the spec.
    15  	// The result must be >= 1.
    16  	Alignof(T Type) int64
    17  
    18  	// Offsetsof returns the offsets of the given struct fields, in bytes.
    19  	// Offsetsof must implement the offset guarantees required by the spec.
    20  	// A negative entry in the result indicates that the struct is too large.
    21  	Offsetsof(fields []*Var) []int64
    22  
    23  	// Sizeof returns the size of a variable of type T.
    24  	// Sizeof must implement the size guarantees required by the spec.
    25  	// A negative result indicates that T is too large.
    26  	Sizeof(T Type) int64
    27  }
    28  
    29  // StdSizes is a convenience type for creating commonly used Sizes.
    30  // It makes the following simplifying assumptions:
    31  //
    32  //   - The size of explicitly sized basic types (int16, etc.) is the
    33  //     specified size.
    34  //   - The size of strings and interfaces is 2*WordSize.
    35  //   - The size of slices is 3*WordSize.
    36  //   - The size of an array of n elements corresponds to the size of
    37  //     a struct of n consecutive fields of the array's element type.
    38  //   - The size of a struct is the offset of the last field plus that
    39  //     field's size. As with all element types, if the struct is used
    40  //     in an array its size must first be aligned to a multiple of the
    41  //     struct's alignment.
    42  //   - All other types have size WordSize.
    43  //   - Arrays and structs are aligned per spec definition; all other
    44  //     types are naturally aligned with a maximum alignment MaxAlign.
    45  //
    46  // *StdSizes implements Sizes.
    47  type StdSizes struct {
    48  	WordSize int64 // word size in bytes - must be >= 4 (32bits)
    49  	MaxAlign int64 // maximum alignment in bytes - must be >= 1
    50  }
    51  
    52  func (s *StdSizes) Alignof(T Type) (result int64) {
    53  	defer func() {
    54  		assert(result >= 1)
    55  	}()
    56  
    57  	// For arrays and structs, alignment is defined in terms
    58  	// of alignment of the elements and fields, respectively.
    59  	switch t := under(T).(type) {
    60  	case *Array:
    61  		// spec: "For a variable x of array type: unsafe.Alignof(x)
    62  		// is the same as unsafe.Alignof(x[0]), but at least 1."
    63  		return s.Alignof(t.elem)
    64  	case *Struct:
    65  		if len(t.fields) == 0 && _IsSyncAtomicAlign64(T) {
    66  			// Special case: sync/atomic.align64 is an
    67  			// empty struct we recognize as a signal that
    68  			// the struct it contains must be
    69  			// 64-bit-aligned.
    70  			//
    71  			// This logic is equivalent to the logic in
    72  			// cmd/compile/internal/types/size.go:calcStructOffset
    73  			return 8
    74  		}
    75  
    76  		// spec: "For a variable x of struct type: unsafe.Alignof(x)
    77  		// is the largest of the values unsafe.Alignof(x.f) for each
    78  		// field f of x, but at least 1."
    79  		max := int64(1)
    80  		for _, f := range t.fields {
    81  			if a := s.Alignof(f.typ); a > max {
    82  				max = a
    83  			}
    84  		}
    85  		return max
    86  	case *Slice, *Interface:
    87  		// Multiword data structures are effectively structs
    88  		// in which each element has size WordSize.
    89  		// Type parameters lead to variable sizes/alignments;
    90  		// StdSizes.Alignof won't be called for them.
    91  		assert(!isTypeParam(T))
    92  		return s.WordSize
    93  	case *Basic:
    94  		// Strings are like slices and interfaces.
    95  		if t.Info()&IsString != 0 {
    96  			return s.WordSize
    97  		}
    98  	case *TypeParam, *Union:
    99  		unreachable()
   100  	}
   101  	a := s.Sizeof(T) // may be 0 or negative
   102  	// spec: "For a variable x of any type: unsafe.Alignof(x) is at least 1."
   103  	if a < 1 {
   104  		return 1
   105  	}
   106  	// complex{64,128} are aligned like [2]float{32,64}.
   107  	if isComplex(T) {
   108  		a /= 2
   109  	}
   110  	if a > s.MaxAlign {
   111  		return s.MaxAlign
   112  	}
   113  	return a
   114  }
   115  
   116  func _IsSyncAtomicAlign64(T Type) bool {
   117  	named := asNamed(T)
   118  	if named == nil {
   119  		return false
   120  	}
   121  	obj := named.Obj()
   122  	return obj.Name() == "align64" &&
   123  		obj.Pkg() != nil &&
   124  		(obj.Pkg().Path() == "sync/atomic" ||
   125  			obj.Pkg().Path() == "runtime/internal/atomic")
   126  }
   127  
   128  func (s *StdSizes) Offsetsof(fields []*Var) []int64 {
   129  	offsets := make([]int64, len(fields))
   130  	var offs int64
   131  	for i, f := range fields {
   132  		if offs < 0 {
   133  			// all remaining offsets are too large
   134  			offsets[i] = -1
   135  			continue
   136  		}
   137  		// offs >= 0
   138  		a := s.Alignof(f.typ)
   139  		offs = align(offs, a) // possibly < 0 if align overflows
   140  		offsets[i] = offs
   141  		if d := s.Sizeof(f.typ); d >= 0 && offs >= 0 {
   142  			offs += d // ok to overflow to < 0
   143  		} else {
   144  			offs = -1 // f.typ or offs is too large
   145  		}
   146  	}
   147  	return offsets
   148  }
   149  
   150  var basicSizes = [...]byte{
   151  	Bool:       1,
   152  	Int8:       1,
   153  	Int16:      2,
   154  	Int32:      4,
   155  	Int64:      8,
   156  	Uint8:      1,
   157  	Uint16:     2,
   158  	Uint32:     4,
   159  	Uint64:     8,
   160  	Float32:    4,
   161  	Float64:    8,
   162  	Complex64:  8,
   163  	Complex128: 16,
   164  }
   165  
   166  func (s *StdSizes) Sizeof(T Type) int64 {
   167  	switch t := under(T).(type) {
   168  	case *Basic:
   169  		assert(isTyped(T))
   170  		k := t.kind
   171  		if int(k) < len(basicSizes) {
   172  			if s := basicSizes[k]; s > 0 {
   173  				return int64(s)
   174  			}
   175  		}
   176  		if k == String {
   177  			return s.WordSize * 2
   178  		}
   179  	case *Array:
   180  		n := t.len
   181  		if n <= 0 {
   182  			return 0
   183  		}
   184  		// n > 0
   185  		esize := s.Sizeof(t.elem)
   186  		if esize < 0 {
   187  			return -1 // element too large
   188  		}
   189  		if esize == 0 {
   190  			return 0 // 0-size element
   191  		}
   192  		// esize > 0
   193  		a := s.Alignof(t.elem)
   194  		ea := align(esize, a) // possibly < 0 if align overflows
   195  		if ea < 0 {
   196  			return -1
   197  		}
   198  		// ea >= 1
   199  		n1 := n - 1 // n1 >= 0
   200  		// Final size is ea*n1 + esize; and size must be <= maxInt64.
   201  		const maxInt64 = 1<<63 - 1
   202  		if n1 > 0 && ea > maxInt64/n1 {
   203  			return -1 // ea*n1 overflows
   204  		}
   205  		return ea*n1 + esize // may still overflow to < 0 which is ok
   206  	case *Slice:
   207  		return s.WordSize * 3
   208  	case *Struct:
   209  		n := t.NumFields()
   210  		if n == 0 {
   211  			return 0
   212  		}
   213  		offsets := s.Offsetsof(t.fields)
   214  		offs := offsets[n-1]
   215  		size := s.Sizeof(t.fields[n-1].typ)
   216  		if offs < 0 || size < 0 {
   217  			return -1 // type too large
   218  		}
   219  		return offs + size // may overflow to < 0 which is ok
   220  	case *Interface:
   221  		// Type parameters lead to variable sizes/alignments;
   222  		// StdSizes.Sizeof won't be called for them.
   223  		assert(!isTypeParam(T))
   224  		return s.WordSize * 2
   225  	case *TypeParam, *Union:
   226  		unreachable()
   227  	}
   228  	return s.WordSize // catch-all
   229  }
   230  
   231  // common architecture word sizes and alignments
   232  var gcArchSizes = map[string]*gcSizes{
   233  	"386":      {4, 4},
   234  	"amd64":    {8, 8},
   235  	"amd64p32": {4, 8},
   236  	"arm":      {4, 4},
   237  	"arm64":    {8, 8},
   238  	"loong64":  {8, 8},
   239  	"mips":     {4, 4},
   240  	"mipsle":   {4, 4},
   241  	"mips64":   {8, 8},
   242  	"mips64le": {8, 8},
   243  	"ppc64":    {8, 8},
   244  	"ppc64le":  {8, 8},
   245  	"riscv64":  {8, 8},
   246  	"s390x":    {8, 8},
   247  	"sparc64":  {8, 8},
   248  	"wasm":     {8, 8},
   249  	// When adding more architectures here,
   250  	// update the doc string of SizesFor below.
   251  }
   252  
   253  // SizesFor returns the Sizes used by a compiler for an architecture.
   254  // The result is nil if a compiler/architecture pair is not known.
   255  //
   256  // Supported architectures for compiler "gc":
   257  // "386", "amd64", "amd64p32", "arm", "arm64", "loong64", "mips", "mipsle",
   258  // "mips64", "mips64le", "ppc64", "ppc64le", "riscv64", "s390x", "sparc64", "wasm".
   259  func SizesFor(compiler, arch string) Sizes {
   260  	switch compiler {
   261  	case "gc":
   262  		if s := gcSizesFor(compiler, arch); s != nil {
   263  			return Sizes(s)
   264  		}
   265  	case "gccgo":
   266  		if s, ok := gccgoArchSizes[arch]; ok {
   267  			return Sizes(s)
   268  		}
   269  	}
   270  	return nil
   271  }
   272  
   273  // stdSizes is used if Config.Sizes == nil.
   274  var stdSizes = SizesFor("gc", "amd64")
   275  
   276  func (conf *Config) alignof(T Type) int64 {
   277  	f := stdSizes.Alignof
   278  	if conf.Sizes != nil {
   279  		f = conf.Sizes.Alignof
   280  	}
   281  	if a := f(T); a >= 1 {
   282  		return a
   283  	}
   284  	panic("implementation of alignof returned an alignment < 1")
   285  }
   286  
   287  func (conf *Config) offsetsof(T *Struct) []int64 {
   288  	var offsets []int64
   289  	if T.NumFields() > 0 {
   290  		// compute offsets on demand
   291  		f := stdSizes.Offsetsof
   292  		if conf.Sizes != nil {
   293  			f = conf.Sizes.Offsetsof
   294  		}
   295  		offsets = f(T.fields)
   296  		// sanity checks
   297  		if len(offsets) != T.NumFields() {
   298  			panic("implementation of offsetsof returned the wrong number of offsets")
   299  		}
   300  	}
   301  	return offsets
   302  }
   303  
   304  // offsetof returns the offset of the field specified via
   305  // the index sequence relative to T. All embedded fields
   306  // must be structs (rather than pointers to structs).
   307  // If the offset is too large (because T is too large),
   308  // the result is negative.
   309  func (conf *Config) offsetof(T Type, index []int) int64 {
   310  	var offs int64
   311  	for _, i := range index {
   312  		s := under(T).(*Struct)
   313  		d := conf.offsetsof(s)[i]
   314  		if d < 0 {
   315  			return -1
   316  		}
   317  		offs += d
   318  		if offs < 0 {
   319  			return -1
   320  		}
   321  		T = s.fields[i].typ
   322  	}
   323  	return offs
   324  }
   325  
   326  // sizeof returns the size of T.
   327  // If T is too large, the result is negative.
   328  func (conf *Config) sizeof(T Type) int64 {
   329  	f := stdSizes.Sizeof
   330  	if conf.Sizes != nil {
   331  		f = conf.Sizes.Sizeof
   332  	}
   333  	return f(T)
   334  }
   335  
   336  // align returns the smallest y >= x such that y % a == 0.
   337  // a must be within 1 and 8 and it must be a power of 2.
   338  // The result may be negative due to overflow.
   339  func align(x, a int64) int64 {
   340  	assert(x >= 0 && 1 <= a && a <= 8 && a&(a-1) == 0)
   341  	return (x + a - 1) &^ (a - 1)
   342  }
   343
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