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Reduce COFF relocation allocation overhead #132933

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Reduce COFF relocation allocation overhead #132933

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3392587
Use value type for COFF relocations
awakecoding Aug 29, 2026
8eca6f0
Remove dedicated COFF writer tests
awakecoding Aug 30, 2026
6ea091b
Mark COFF relocation write readonly
awakecoding Aug 30, 2026
cc34c7c
Remove redundant readonly modifier
awakecoding Aug 30, 2026
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58 changes: 31 additions & 27 deletions src/coreclr/tools/Common/Compiler/ObjectWriter/CoffObjectWriter.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -291,19 +291,21 @@ private protected override void EmitRelocations(int sectionIndex, List<SymbolicR
// Write an overflow relocation with the real count of relocations
sectionHeader.NumberOfRelocations = ushort.MaxValue;
sectionHeader.SectionCharacteristics |= SectionCharacteristics.LinkerNRelocOvfl;
coffRelocations.Add(new CoffRelocation { VirtualAddress = (uint)(relocationList.Count + 1) });
coffRelocations.Add(new CoffRelocation(
(uint)(relocationList.Count + 1),
symbolTableIndex: 0,
type: 0));
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}

switch (_machine)
{
case Machine.I386:
foreach (var relocation in relocationList)
{
coffRelocations.Add(new CoffRelocation
{
VirtualAddress = (uint)relocation.Offset,
SymbolTableIndex = _symbolNameToIndex[relocation.SymbolName],
Type = relocation.Type switch
coffRelocations.Add(new CoffRelocation(
(uint)relocation.Offset,
_symbolNameToIndex[relocation.SymbolName],
relocation.Type switch
{
IMAGE_REL_BASED_ABSOLUTE => IMAGE_REL_I386_DIR32NB,
IMAGE_REL_BASED_ADDR32NB => IMAGE_REL_I386_DIR32NB,
Expand All @@ -313,19 +315,17 @@ private protected override void EmitRelocations(int sectionIndex, List<SymbolicR
IMAGE_REL_SECREL => IMAGE_REL_I386_SECREL,
IMAGE_REL_SECTION => IMAGE_REL_I386_SECTION,
_ => throw new NotSupportedException($"Unsupported relocation: {relocation.Type}")
},
});
}));
}
break;

case Machine.Amd64:
foreach (var relocation in relocationList)
{
coffRelocations.Add(new CoffRelocation
{
VirtualAddress = (uint)relocation.Offset,
SymbolTableIndex = _symbolNameToIndex[relocation.SymbolName],
Type = relocation.Type switch
coffRelocations.Add(new CoffRelocation(
(uint)relocation.Offset,
_symbolNameToIndex[relocation.SymbolName],
relocation.Type switch
{
IMAGE_REL_BASED_ABSOLUTE => IMAGE_REL_AMD64_ADDR32NB,
IMAGE_REL_BASED_ADDR32NB => IMAGE_REL_AMD64_ADDR32NB,
Expand All @@ -336,19 +336,17 @@ private protected override void EmitRelocations(int sectionIndex, List<SymbolicR
IMAGE_REL_SECREL => IMAGE_REL_AMD64_SECREL,
IMAGE_REL_SECTION => IMAGE_REL_AMD64_SECTION,
_ => throw new NotSupportedException($"Unsupported relocation: {relocation.Type}")
},
});
}));
}
break;

case Machine.Arm64:
foreach (var relocation in relocationList)
{
coffRelocations.Add(new CoffRelocation
{
VirtualAddress = (uint)relocation.Offset,
SymbolTableIndex = _symbolNameToIndex[relocation.SymbolName],
Type = relocation.Type switch
coffRelocations.Add(new CoffRelocation(
(uint)relocation.Offset,
_symbolNameToIndex[relocation.SymbolName],
relocation.Type switch
{
IMAGE_REL_BASED_ABSOLUTE => IMAGE_REL_ARM64_ADDR32NB,
IMAGE_REL_BASED_ADDR32NB => IMAGE_REL_ARM64_ADDR32NB,
Expand All @@ -365,8 +363,7 @@ private protected override void EmitRelocations(int sectionIndex, List<SymbolicR
IMAGE_REL_SECREL => IMAGE_REL_ARM64_SECREL,
IMAGE_REL_SECTION => IMAGE_REL_ARM64_SECTION,
_ => throw new NotSupportedException($"Unsupported relocation: {relocation.Type}")
},
});
}));
}
break;

Expand Down Expand Up @@ -454,7 +451,7 @@ private protected override void EmitObjectFile(Stream outputFileStream)

if (section.Relocations.Count > 0)
{
foreach (var relocation in section.Relocations)
foreach (ref readonly CoffRelocation relocation in CollectionsMarshal.AsSpan(section.Relocations))
{
relocation.Write(outputFileStream);
}
Expand Down Expand Up @@ -700,11 +697,18 @@ internal enum CoffRelocationType
IMAGE_REL_ARM64_REL32 = 17,
}

protected sealed class CoffRelocation
internal readonly struct CoffRelocation
{
public uint VirtualAddress { get; set; }
public uint SymbolTableIndex { get; set; }
public CoffRelocationType Type { get; set; }
public CoffRelocation(uint virtualAddress, uint symbolTableIndex, CoffRelocationType type)
{
VirtualAddress = virtualAddress;
SymbolTableIndex = symbolTableIndex;
Type = type;
}

public uint VirtualAddress { get; }
public uint SymbolTableIndex { get; }
public CoffRelocationType Type { get; }

public const int Size =
sizeof(uint) + // VirtualAddress
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