Invoking an unmanaged fastcall function pointer under x86 Windows fails at runtime
Nobody has claimed this yet.
Assessment
- Difficulty
- 4/5
- Estimated time
- 3-5 days
- Newbie friendliness
- 35/100
- Issue type
- Bug
- Clarity
- Mostly clear
- Activity status
- Stale
- Tech stack
- csharp
- Domain
- backend, operating-systems
Research direction
Start with the Windows x86 calling-convention handling in src/coreclr/vm/dllimport.cpp around line 4238. Reproduce the TypeLoadException using the provided unsafe C# function-pointer example and inspect how Fastcall is handled. Done means the UnmanagedCallersOnly Fastcall pointer invocation works on Windows x86 without the unsupported-calling-convention failure.
Written by the indexing model from the issue text.
Description
Description
Exporting a function using UnmanagedCallersOnly and the Fastcall calling convention will work, but calling ((delegate* unmanaged[Fastcall]<int, int>)somePtr)(someArg) will fail with
System.TypeLoadException
HResult=0x80131522
Message=Unsupported unmanaged calling convention.
Reproduction Steps
unsafe
{
int x = ((delegate* unmanaged[Fastcall]<int, int>)IntPtr.Zero)(0);
}
Expected behavior
The function pointer should be called.
Actual behavior
The call fails due to the Fastcall calling convention being unimplemented.
Regression?
Unlikely that this was implemented before and removed afterwards.
Known Workarounds
No response
Configuration
Windows x86
Technically I'm running from a CoreCLR embedded in an application, but it should not matter in this scenario.
Other information
- Dominant language
- C#
- Stars
- 18.3k
- Forks
- 5.6k
- PR merge metrics
- PR metrics pending
Contributor guide
First steps
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- Open a pull request that references the issue number.
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