[clr-ios] Use IL unboxing stubs when FEATURE_JIT isn't available #121115
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Pull Request Overview
This PR addresses a critical runtime issue on iOS and other Apple mobile platforms where dynamic code generation is prohibited due to W^X (write XOR execute) memory protection and code-signing restrictions. The change prevents the runtime from attempting to emit native ARM64 machine code at execution time for unboxing and instantiating stubs.
Key Changes:
- Renamed
FEATURE_PORTABLE_SHUFFLE_THUNKStoFEATURE_SHUFFLE_THUNKSand made it conditional onFEATURE_JITavailability - Extended ARM64 platforms to use IL-based stubs instead of runtime code generation when JIT is unavailable
- Updated conditional compilation directives across multiple files to respect the new feature flag semantics
Reviewed Changes
Copilot reviewed 7 out of 7 changed files in this pull request and generated 2 comments.
Show a summary per file
| File | Description |
|---|---|
| src/coreclr/inc/switches.h | Modified feature flag definition to only enable shuffle thunks when JIT is available |
| src/coreclr/vm/prestub.cpp | Updated conditional compilation to use renamed feature flag for stub selection logic |
| src/coreclr/vm/i386/stublinkerx86.h | Changed guard condition for EmitUnboxMethodStub declaration from TARGET_X86 to feature-based check |
| src/coreclr/vm/i386/stublinkerx86.cpp | Updated conditional compilation for EmitUnboxMethodStub implementation |
| src/coreclr/vm/comdelegate.cpp | Reorganized shuffle array generation logic to use feature flag instead of platform-specific checks |
| src/coreclr/vm/arm64/stubs.cpp | Added ARM64 implementation of EmitUnboxMethodStub for non-JIT scenarios |
| src/coreclr/vm/arm64/cgencpu.h | Added EmitUnboxMethodStub method declaration guarded by feature flag |
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Tagging subscribers to this area: @BrzVlad, @janvorli, @kg |
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@kotlarmilos Could you please check whether it is still fixing the problem that it was meant to fix? |
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Thanks Jan, this was educational :) I confirm it fixes dynamic code generation for MakeUnboxingStubWorker and MakeInstantiatingStubWorker. |
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/ba-g infrastructure timeouts |
4 participants
Description
This change prevents the runtime from emitting native machine code at execution time through StubLinkerCPU on platforms where dynamic code generation is not allowed due to W^X and code-signing restrictions. Currently, unboxing and generic instantiating stubs still generate arm64 code via CPUSTUBLINKER that works as a lightweight JIT, because FEATURE_PORTABLE_SHUFFLE_THUNKS is enabled on all non-x86 targets.
Changes
This PR renames FEATURE_PORTABLE_SHUFFLE_THUNKS to FEATURE_SHUFFLE_THUNKS and only enables it when FEATURE_JIT is available. This instructs Apple mobile to use IL-based unboxing and instantiating stubs instead of emitting code at runtime, avoiding invalid memory execution.