Crossgen2: Support Writing R2R Metadata into Wasm Data Sections in Wasm Object Writer #122878
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…nd begin internally sorting non-code R2R nodes into WasmData type sections
…py R2R data into these segments
src/coreclr/tools/Common/Compiler/ObjectWriter/CodeDataLayoutMode.cs
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| if (_insPaddingByte.HasValue) | ||
| { | ||
| sectionData = new SectionData(section.Type == SectionType.Executable ? _insPaddingByte.Value : (byte)0); | ||
| } | ||
| else | ||
| { | ||
| sectionData = new SectionData(); | ||
| } | ||
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Why not just use 0 as the padding byte for executable sections for wasm (that's the default padding)?
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Yeah good call, that would work as well here.
| GetOrCreateSection(ObjectNodeSection.ManagedCodeWindowsContentSection); | ||
| } | ||
| else | ||
| else if (_nodeFactory.Target.OperatingSystem != TargetOS.Browser) |
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Once #122511 is in, we should remove this OS check and instead handle this with an override of GetEmitSection in WasmObjectWriter.
| // Write the number of functions | ||
| writer.WriteULEB128((ulong)methodBodies.Count); | ||
| for (int i = 0; i < methodBodies.Count; i++) |
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For these array-based sections, could we do the following?
- Skip the "count" header.
- When a node for such a section is seen, emit the data into the section and record that we emitted a node into the section.
- When emitting the object file, emit the "count" header before emitting the section data.
With this design, we could avoid having this split between "emit into the section as we process the nodes" and "emit at the end".
| public static readonly ObjectNodeSection WasmCodeSection = new ObjectNodeSection("wasm.code", SectionType.Executable, needsAlign: false); | ||
| // TODO-Wasm: consider alignment of data sections | ||
| public static readonly ObjectNodeSection WasmDataSection = new ObjectNodeSection("wasm.data", SectionType.Writeable, needsAlign: false); | ||
| public static readonly ObjectNodeSection WasmFunctionSection = new ObjectNodeSection("wasm.function", SectionType.ReadOnly, needsAlign: false); | ||
| public static readonly ObjectNodeSection WasmTypeSection = new ObjectNodeSection("wasm.type", SectionType.ReadOnly, needsAlign: false); | ||
| public static readonly ObjectNodeSection WasmExportSection = new ObjectNodeSection("wasm.export", SectionType.ReadOnly, needsAlign: false); | ||
| public static readonly ObjectNodeSection WasmMemorySection = new ObjectNodeSection("wasm.memory", SectionType.ReadOnly, needsAlign: false); |
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If these sections won't be returned by ObjectNode.GetSection, then they should be defined in WasmObjectWriter.
| // Text section will have already been created by the base class when this method is called | ||
| GetOrCreateSection(ObjectNodeSection.WasmMemorySection); | ||
| GetOrCreateSection(ObjectNodeSection.WasmTypeSection); | ||
| GetOrCreateSection(ObjectNodeSection.WasmFunctionSection); | ||
| GetOrCreateSection(ObjectNodeSection.WasmExportSection); |
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If these don't need to be created in a particular order, it's fine to let them get created at use time (first usage of GetOrCreateSection elsewhere for a given section).
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They don't need to be created in a particular order so I think I can change to the approach you're suggesting and remove this!
Co-authored-by: Jeremy Koritzinsky <jkoritzinsky@gmail.com>
| // Write the data if: | ||
| // 1. We are in unified code/data layout mode so separating code and data nodes doesn't matter, OR | ||
| // 2. We are in separate code data layout mode but are writing data nodes | ||
| // Note that this has to be done last as not to advance the section writer position. | ||
| if (LayoutMode == CodeDataLayout.Unified || node.GetSection(_nodeFactory) != ObjectNodeSection.TextSection) | ||
| { | ||
| sectionWriter.EmitData(nodeContents.Data); | ||
| } |
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If we change RecordMethod to only write the signature into the signature table and the signature index into the function table, we should be able to change this code to just emit the data directly.
I guess we'd need a way to also prepend length here. We could do that with a bool property that wasm sets (and we only do it for when that property is true and we're emitting into the text section).
Or, we could add a feature to the section writer so the writer for the Text section always prepends length.
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