Set AssemblyName.ProcessorArchitecture for compatibility.

[VSadov]

Fixes: #77697

Computing and setting ProcessorArchitecture was unintentionally omitted when GetAssemblyName(path) was switched to a managed implementation.

This will need to be backported to 7.0

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Issue Details

---

Fixes: #77697

ProcessorArchitecture was unintentionally omitted when GetAssemblyName(path) was switched to a managed implementation.

Author:	VSadov
Assignees:	-
Labels:	area-System.Reflection.Metadata
Milestone:	-

[jkotas]

Any idea what this is trying to check for?

[VSadov]

There is one place that calls 0xF0 is ProcArchMask

runtime/src/libraries/System.Private.CoreLib/src/System/Reflection/AssemblyNameFlags.cs

Line 13 in 57bfe47

// ProcArchMask = 0x00F0, // Bits describing the processor architecture

I suspect 0x70 means None, but that is just a guess.

[VSadov]

Old NDP sources have this:

            // 0x70 specifies "reference assembly", a new concept in v4.0. For these, CLR wants to return None as arch so they
            // can be always loaded, regardless of process type. 

[VSadov]

I've checked a few reference assemblies. The COFF header specifies machine as I386 and CorFlags are ILOnly, so this does look like needs to be handled in a special way.
Otherwise the suggested simplified way will return MSIL while expected to return None

[jkotas]

I think that this logic is very convoluted. I would simplify into something that one can reason about. For example:

assemblyName.ProcessorArchitecture = peHeaders.CoffHeader.Machine switch
{
    ImageFileMachine.I386 => IsPlatformNeutral(peHeaders.CorHeader!.Flags) ? ProcessorArchitecture.MSIL : ProcessorArchitecture.X86;
    ImageFileMachine.AMD64 => ProcessorArchitecture.Amd64,
    ImageFileMachine.ARM => ProcessorArchitecture.Arm,    
    ImageFileMachine.IA64 => ProcessorArchitecture.IA64,
    _ => ProcessorArchitecture.None
}

static bool IsPlatformNeutral(CorFlags flags) =>
   ((flags & CorFlags.ILOnly) != 0) && ((flags & (CorFlags.Requires32Bit | CorFlags.Prefers32Bit) != CorFlags.Requires32Bit);

It will behave differently from the current convoluted logic for invalid images (ie images that would not execute anyway - like x86 image with PE32+ header, etc.). I think that it is ok.

[jkotas]

We can potentially apply the same simplification in the CoreCLR copy as well.

[VSadov]

We can potentially apply the same simplification in the CoreCLR copy as well.

Yes. I think we might be ok with duplication, since this is legacy and will not change often, if at all, and only needed in two places. But if implementations do not match, it could be confusing why the differences.

[jkotas]

LGTM!

[VSadov]

Thanks!!

[VSadov]

/backport to release/7.0

[github-actions]

Started backporting to release/7.0: https://github.com/dotnet/runtime/actions/runs/3998851487