[wasm coreclr] Fix fields alignment #115364
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Fixes dotnet#115363 The problem happened in MethodTableBuilder::PlaceInstanceFields where in wasm case the fields were placed at wrong offsets. The native representation looks like this: ``` class field wasm type offset ----------------------------------------------------------------------------------------------- Object PTR_MethodTable m_pMethTab i32 0 AssemblyLoadContextBaseObject int64_t _id i64 8 OBJECTREF _unloadLock i32 12 OBJECTREF _resolvingUnmanagedDll i32 OBJECTREF _resolving i32 OBJECTREF _unloading i32 OBJECTREF _name i32 INT_PTR _nativeAssemblyLoadContext i32 DWORD _state i32 40 CLR_BOOL _isCollectible i8 44 ``` While the managed field offsets were calculated wrong, the _id was placed at offset 4 and thus all the following fields were at wrong offsets too. The size check then failed. By enabling FEATURE_64BIT_ALIGNMENT the dwOffsetBias is set to TARGET_POINTER_SIZE and the fields layout is calculated properly. The 8 bytes types in wasm should be aligned to 8 bytes https://github.com/WebAssembly/tool-conventions/blob/main/BasicCABI.md#data-representation so hopefully the rest of the changes enabled by this feature should apply as well. Before this feature was enabled only for arm 32bits.
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Pull Request Overview
This PR fixes field alignment issues in wasm CoreCLR by correcting the managed field offset calculation.
- Expanded the 64-bit alignment feature to include the wasm platform using the TARGET_BROWSER flag.
- Updates in both switches.h and gcenv.object.h files enable proper alignment for 8-byte types on wasm.
Reviewed Changes
Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.
| File | Description |
|---|---|
| src/coreclr/inc/switches.h | Added TARGET_BROWSER to enable FEATURE_64BIT_ALIGNMENT |
| src/coreclr/gc/env/gcenv.object.h | Added TARGET_BROWSER to enable FEATURE_64BIT_ALIGNMENT |
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Fixes #115363
The problem happened in
MethodTableBuilder::PlaceInstanceFieldswhere in wasm case the fields were placed at wrong offsets.The native representation looks like this:
While the managed field offsets were calculated wrong, the _id was placed at offset 4 and thus all the following fields were at wrong offsets too. The size check then failed.
By enabling
FEATURE_64BIT_ALIGNMENTthedwOffsetBiasis set toTARGET_POINTER_SIZEand the fields layout is calculated properly.The 8 bytes wide types in wasm should be aligned to 8 bytes
https://github.com/WebAssembly/tool-conventions/blob/main/BasicCABI.md#data-representation
so hopefully the rest of the changes enabled by this feature should apply as well. Before this feature was enabled only for arm 32bits.