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| 1 | +// Copyright 2023 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 types2 |
| 6 | + |
| 7 | +type gcSizes struct { |
| 8 | + WordSize int64 // word size in bytes - must be >= 4 (32bits) |
| 9 | + MaxAlign int64 // maximum alignment in bytes - must be >= 1 |
| 10 | +} |
| 11 | + |
| 12 | +func (s *gcSizes) Alignof(T Type) (result int64) { |
| 13 | + defer func() { |
| 14 | + assert(result >= 1) |
| 15 | + }() |
| 16 | + |
| 17 | + // For arrays and structs, alignment is defined in terms |
| 18 | + // of alignment of the elements and fields, respectively. |
| 19 | + switch t := under(T).(type) { |
| 20 | + case *Array: |
| 21 | + // spec: "For a variable x of array type: unsafe.Alignof(x) |
| 22 | + // is the same as unsafe.Alignof(x[0]), but at least 1." |
| 23 | + return s.Alignof(t.elem) |
| 24 | + case *Struct: |
| 25 | + if len(t.fields) == 0 && IsSyncAtomicAlign64(T) { |
| 26 | + // Special case: sync/atomic.align64 is an |
| 27 | + // empty struct we recognize as a signal that |
| 28 | + // the struct it contains must be |
| 29 | + // 64-bit-aligned. |
| 30 | + // |
| 31 | + // This logic is equivalent to the logic in |
| 32 | + // cmd/compile/internal/types/size.go:calcStructOffset |
| 33 | + return 8 |
| 34 | + } |
| 35 | + |
| 36 | + // spec: "For a variable x of struct type: unsafe.Alignof(x) |
| 37 | + // is the largest of the values unsafe.Alignof(x.f) for each |
| 38 | + // field f of x, but at least 1." |
| 39 | + max := int64(1) |
| 40 | + for _, f := range t.fields { |
| 41 | + if a := s.Alignof(f.typ); a > max { |
| 42 | + max = a |
| 43 | + } |
| 44 | + } |
| 45 | + return max |
| 46 | + case *Slice, *Interface: |
| 47 | + // Multiword data structures are effectively structs |
| 48 | + // in which each element has size WordSize. |
| 49 | + // Type parameters lead to variable sizes/alignments; |
| 50 | + // StdSizes.Alignof won't be called for them. |
| 51 | + assert(!isTypeParam(T)) |
| 52 | + return s.WordSize |
| 53 | + case *Basic: |
| 54 | + // Strings are like slices and interfaces. |
| 55 | + if t.Info()&IsString != 0 { |
| 56 | + return s.WordSize |
| 57 | + } |
| 58 | + case *TypeParam, *Union: |
| 59 | + unreachable() |
| 60 | + } |
| 61 | + a := s.Sizeof(T) // may be 0 or negative |
| 62 | + // spec: "For a variable x of any type: unsafe.Alignof(x) is at least 1." |
| 63 | + if a < 1 { |
| 64 | + return 1 |
| 65 | + } |
| 66 | + // complex{64,128} are aligned like [2]float{32,64}. |
| 67 | + if isComplex(T) { |
| 68 | + a /= 2 |
| 69 | + } |
| 70 | + if a > s.MaxAlign { |
| 71 | + return s.MaxAlign |
| 72 | + } |
| 73 | + return a |
| 74 | +} |
| 75 | + |
| 76 | +func (s *gcSizes) Offsetsof(fields []*Var) []int64 { |
| 77 | + offsets := make([]int64, len(fields)) |
| 78 | + var offs int64 |
| 79 | + for i, f := range fields { |
| 80 | + if offs < 0 { |
| 81 | + // all remaining offsets are too large |
| 82 | + offsets[i] = -1 |
| 83 | + continue |
| 84 | + } |
| 85 | + // offs >= 0 |
| 86 | + a := s.Alignof(f.typ) |
| 87 | + offs = align(offs, a) // possibly < 0 if align overflows |
| 88 | + offsets[i] = offs |
| 89 | + if d := s.Sizeof(f.typ); d >= 0 && offs >= 0 { |
| 90 | + offs += d // ok to overflow to < 0 |
| 91 | + } else { |
| 92 | + offs = -1 // f.typ or offs is too large |
| 93 | + } |
| 94 | + } |
| 95 | + return offsets |
| 96 | +} |
| 97 | + |
| 98 | +func (s *gcSizes) Sizeof(T Type) int64 { |
| 99 | + switch t := under(T).(type) { |
| 100 | + case *Basic: |
| 101 | + assert(isTyped(T)) |
| 102 | + k := t.kind |
| 103 | + if int(k) < len(basicSizes) { |
| 104 | + if s := basicSizes[k]; s > 0 { |
| 105 | + return int64(s) |
| 106 | + } |
| 107 | + } |
| 108 | + if k == String { |
| 109 | + return s.WordSize * 2 |
| 110 | + } |
| 111 | + case *Array: |
| 112 | + n := t.len |
| 113 | + if n <= 0 { |
| 114 | + return 0 |
| 115 | + } |
| 116 | + // n > 0 |
| 117 | + esize := s.Sizeof(t.elem) |
| 118 | + if esize < 0 { |
| 119 | + return -1 // element too large |
| 120 | + } |
| 121 | + if esize == 0 { |
| 122 | + return 0 // 0-size element |
| 123 | + } |
| 124 | + // esize > 0 |
| 125 | + // Final size is esize * n; and size must be <= maxInt64. |
| 126 | + const maxInt64 = 1<<63 - 1 |
| 127 | + if esize > maxInt64/n { |
| 128 | + return -1 // esize * n overflows |
| 129 | + } |
| 130 | + return esize * n |
| 131 | + case *Slice: |
| 132 | + return s.WordSize * 3 |
| 133 | + case *Struct: |
| 134 | + n := t.NumFields() |
| 135 | + if n == 0 { |
| 136 | + return 0 |
| 137 | + } |
| 138 | + offsets := s.Offsetsof(t.fields) |
| 139 | + offs := offsets[n-1] |
| 140 | + size := s.Sizeof(t.fields[n-1].typ) |
| 141 | + if offs < 0 || size < 0 { |
| 142 | + return -1 // type too large |
| 143 | + } |
| 144 | + // gc: The last field of a non-zero-sized struct is not allowed to |
| 145 | + // have size 0. |
| 146 | + if offs > 0 && size == 0 { |
| 147 | + size = 1 |
| 148 | + } |
| 149 | + // gc: Size includes alignment padding. |
| 150 | + return align(offs+size, s.Alignof(t)) // may overflow to < 0 which is ok |
| 151 | + case *Interface: |
| 152 | + // Type parameters lead to variable sizes/alignments; |
| 153 | + // StdSizes.Sizeof won't be called for them. |
| 154 | + assert(!isTypeParam(T)) |
| 155 | + return s.WordSize * 2 |
| 156 | + case *TypeParam, *Union: |
| 157 | + unreachable() |
| 158 | + } |
| 159 | + return s.WordSize // catch-all |
| 160 | +} |
| 161 | + |
| 162 | +// gcSizesFor returns the Sizes used by gc for an architecture. |
| 163 | +// The result is nil if a compiler/architecture pair is not known. |
| 164 | +func gcSizesFor(compiler, arch string) *gcSizes { |
| 165 | + if compiler != "gc" { |
| 166 | + return nil |
| 167 | + } |
| 168 | + return gcArchSizes[arch] |
| 169 | +} |
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