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C++: Fix calculation of alignment for some structs

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This commit is contained in:
Katy Coe
2020-08-13 06:56:05 +02:00
parent 8609523eba
commit 75de69e338
1 changed files with 34 additions and 7 deletions
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41
Il2CppInspector.Common/Cpp/CppType.cs
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@@ -239,23 +239,50 @@ namespace Il2CppInspector.Cpp
// Unions and bitfields can have more than one field at the same offset
public SortedDictionary<int, List<CppField>> Fields { get; internal set; } = new SortedDictionary<int, List<CppField>>();
public CppComplexType(ComplexValueType complexValueType) : base("", 0) => ComplexValueType = complexValueType;
public CppComplexType(ComplexValueType complexValueType) : base("", 0) {
ComplexValueType = complexValueType;
// An empty class shall always have sizeof() >= 1
// This will get overwritten the first time a field is added
Size = 8;
}
// Add a field to the type. Returns the offset of the field in the type
public int AddField(CppField field, int alignmentBytes = 0) {
// Unions and enums always have an offset of zero
field.Offset = ComplexValueType == ComplexValueType.Struct ? Size : 0;
// An empty struct has a Size (bits) of 8 so the first field must also be set to zero offset
field.Offset = ComplexValueType == ComplexValueType.Struct ? (Fields.Any()? Size : 0) : 0;
// If we just came out of a bitfield, move to the next byte if necessary
if (field.BitfieldSize == 0 && field.Offset % 8 != 0)
field.Offset = (field.Offset / 8) * 8 + 8;
// A struct or union must be aligned on a word boundary for the architecture bit width
//if (field.Type is CppComplexType &&
// A 2, 4 or 8-byte value etc. must be aligned on an equivalent boundary
if (!(field.Type is CppComplexType) && field.OffsetBytes % field.SizeBytes != 0)
field.Offset += (field.SizeBytes - field.OffsetBytes % field.SizeBytes) * 8;
// The same goes for the first entry in a struct, union or array
// This block searches depth-first for the first field or element in any child types to find the required alignment boundary
// https://en.wikipedia.org/wiki/Data_structure_alignment
if (field.BitfieldSize == 0) {
var firstSimpleType = field.Type;
var foundType = false;
while (!foundType) {
var simpleType = firstSimpleType switch {
CppAlias alias => alias.ElementType,
CppComplexType { ComplexValueType: ComplexValueType.Struct } complex => complex.Fields.FirstOrDefault().Value?.First().Type,
CppArrayType array => array.ElementType,
_ => firstSimpleType
};
if (simpleType == firstSimpleType)
foundType = true;
firstSimpleType = simpleType;
}
// Empty classes shall always have sizeof() >= 1 and alignment doesn't matter
// Empty classes will be returned as null by the above code (complex? null conditional operator)
// https://www.stroustrup.com/bs_faq2.html#sizeof-empty
if (firstSimpleType != null)
if (field.OffsetBytes % firstSimpleType.SizeBytes != 0)
field.Offset += (firstSimpleType.SizeBytes - field.OffsetBytes % firstSimpleType.SizeBytes) * 8;
}
// Respect alignment directives
if (alignmentBytes > 0 && field.OffsetBytes % alignmentBytes != 0)