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https://github.com/JakeHillion/object-introspection.git
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AddPadding: Always pad bitfields with "int8_t"s
The underlying type of bitfield is important to the size of a struct: struct Foo { int64_t bitfield : 1; }; struct Bar { int8_t bitfield : 1; }; sizeof(Foo) = 8; sizeof(Bar) = 1;
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@ -130,16 +130,24 @@ void AddPadding::addPadding(uint64_t paddingStartBits,
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if (paddingBits == 0)
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return;
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if (paddingBits % 8 == 0) {
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// Pad with an array of bytes
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auto& primitive = typeGraph_.makeType<Primitive>(Primitive::Kind::Int8);
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auto& paddingArray = typeGraph_.makeType<Array>(primitive, paddingBits / 8);
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paddedMembers.emplace_back(paddingArray, MemberPrefix, paddingStartBits);
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} else {
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// Pad with a bitfield
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auto& primitive = typeGraph_.makeType<Primitive>(Primitive::Kind::Int64);
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// We must only use Int8s for padding in order to not accidentally increase
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// the alignment requirements of this type. This applies to bitfield padding
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// as well.
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auto& primitive = typeGraph_.makeType<Primitive>(Primitive::Kind::Int8);
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if (paddingBits % 8 != 0) {
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// Pad with a bitfield up to the next byte
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paddedMembers.emplace_back(primitive, MemberPrefix, paddingStartBits,
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paddingBits);
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paddingBits % 8);
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}
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uint64_t paddingBytes = paddingBits / 8;
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if (paddingBytes > 0) {
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// Pad with an array of bytes
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uint64_t paddingStartByte = (paddingStartBits + 7) / 8;
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auto& paddingArray = typeGraph_.makeType<Array>(primitive, paddingBytes);
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paddedMembers.emplace_back(paddingArray, MemberPrefix,
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paddingStartByte * 8);
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}
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}
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@ -124,20 +124,23 @@ TEST(AddPaddingTest, Bitfields) {
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Member: b2 (offset: 0.375, bitsize: 2)
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Primitive: int8_t
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Member: __oi_padding (offset: 0.625, bitsize: 3)
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Primitive: int64_t
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Primitive: int8_t
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Member: b3 (offset: 1, bitsize: 1)
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Primitive: int8_t
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Member: __oi_padding (offset: 1.125, bitsize: 55)
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Primitive: int64_t
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Member: __oi_padding (offset: 1.125, bitsize: 7)
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Primitive: int8_t
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Member: __oi_padding (offset: 2)
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[1] Array: (length: 6)
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Primitive: int8_t
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Member: b4 (offset: 8, bitsize: 24)
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Primitive: int64_t
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Member: __oi_padding (offset: 11)
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[1] Array: (length: 1)
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[2] Array: (length: 1)
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Primitive: int8_t
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Member: n (offset: 12)
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Primitive: int16_t
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Member: __oi_padding (offset: 14)
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[2] Array: (length: 2)
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[3] Array: (length: 2)
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Primitive: int8_t
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)");
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}
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