ilasm does not apply multiple custom attributes on interface implementations

[ltrzesniewski]

Description

I believe the following code:

.interfaceimpl type ITestInterface
.custom instance void Test1Attribute::.ctor() = ( 01 00 00 00 )
.custom instance void Test2Attribute::.ctor() = ( 01 00 00 00 )

is supposed to apply two attributes on the interface implementation.

When round-tripped through ilasm/ildasm, this code is turned into:

.custom instance void Test2Attribute::.ctor() = ( 01 00 00 00 ) 
.interfaceimpl type ITestInterface
.custom instance void Test1Attribute::.ctor() = ( 01 00 00 00 ) 

Which means:

• Test1Attribute is applied on the interface implementation (metadata table 09)
• Test2Attribute is applied on the type definition (metadata table 02)

The CustomAttribute metadata table shows that ildasm is correct here:

In addition, note that the following code produces the desired effect in ilasm:

.interfaceimpl type ITestInterface
.custom instance void Test1Attribute::.ctor() = ( 01 00 00 00 )
.interfaceimpl type ITestInterface
.custom instance void Test2Attribute::.ctor() = ( 01 00 00 00 )

But in that case, ildasm decompiles it to:

.interfaceimpl type ITestInterface
.custom instance void Test1Attribute::.ctor() = ( 01 00 00 00 ) 
.custom instance void Test2Attribute::.ctor() = ( 01 00 00 00 ) 

Which doesn't round-trip.

Reproduction Steps

Here is a test file, Test.il:

.assembly extern mscorlib
{
	.publickeytoken = ( b7 7a 5c 56 19 34 e0 89	)
	.ver 4:0:0:0
}
.assembly Test
{
	.hash algorithm 0x00008004 // SHA1
	.ver 1:0:0:0
}

.module Test.dll
.imagebase 0x10000000
.file alignment 0x00000200
.stackreserve 0x00100000
.subsystem 0x0003 // WindowsCui
.corflags 0x00000001 // ILOnly

.class private auto ansi '<Module>'
{
}

.class public auto ansi beforefieldinit TestType
    extends [mscorlib]System.Object
	implements ITestInterface
{
    .interfaceimpl type ITestInterface
    .custom instance void Test1Attribute::.ctor() = ( 01 00 00 00 )
    .custom instance void Test2Attribute::.ctor() = ( 01 00 00 00 )

    .method public hidebysig specialname rtspecialname
        instance void .ctor () cil managed
    {
        .maxstack 8

        IL_0000: ldarg.0
        IL_0001: call instance void [mscorlib]System.Object::.ctor()
        IL_0006: ret
    }
}

.class interface public auto ansi abstract ITestInterface
{
}

.class public auto ansi beforefieldinit Test1Attribute
    extends [mscorlib]System.Attribute
{
    .method public hidebysig specialname rtspecialname
        instance void .ctor () cil managed
    {
        .maxstack 8

        IL_0000: ldarg.0
        IL_0001: call instance void [mscorlib]System.Attribute::.ctor()
        IL_0006: ret
    }
}

.class public auto ansi beforefieldinit Test2Attribute
    extends [mscorlib]System.Attribute
{
    .method public hidebysig specialname rtspecialname
        instance void .ctor () cil managed
    {
        .maxstack 8

        IL_0000: ldarg.0
        IL_0001: call instance void [mscorlib]System.Attribute::.ctor()
        IL_0006: ret
    }
}

• Compile it with ilasm /DLL Test.il
• Decompile it with ildasm /OUT=TestOut.il Test.dll

Expected behavior

• Both Test1Attribute and Test2Attribute should be applied on the interface implementation (metadata table 09: InterfaceImpl)
• This shouldn't change when the code is round-tripped through ilasm/ildasm

Actual behavior

• Test1Attribute is applied on the interface implementation (metadata table 09: InterfaceImpl)
• Test2Attribute is applied on the type definition (metadata table 02: TypeDef)

Regression?

Not as far as I can tell.

Known Workarounds

Repeat .interfaceimpl type for each .custom instance to apply the custom attribute to the interface implementation.

No workaround for the round-trip inconsistency though.

Configuration

Tested with ilasm/ildasm from:

• the current main: 5ac3de1
• Microsoft.NETCore.ILAsm/Microsoft.NETCore.ILDAsm NuGet packages v6.0.0

(why are the v7.0.0 packages empty BTW?)

Other information

No response

[ghost]

Tagging subscribers to this area: @JulieLeeMSFT
See info in area-owners.md if you want to be subscribed.

Issue Details

---

Description

I believe the following code:

.interfaceimpl type ITestInterface
.custom instance void Test1Attribute::.ctor() = ( 01 00 00 00 )
.custom instance void Test2Attribute::.ctor() = ( 01 00 00 00 )

is supposed to apply two attributes on the interface implementation.

When round-tripped through ilasm/ildasm, this code is turned into:

.custom instance void Test2Attribute::.ctor() = ( 01 00 00 00 ) 
.interfaceimpl type ITestInterface
.custom instance void Test1Attribute::.ctor() = ( 01 00 00 00 ) 

Which means:

• Test1Attribute is applied on the interface implementation (metadata table 09)
• Test2Attribute is applied on the type definition (metadata table 02)

The CustomAttribute metadata table shows that ildasm is correct here:

In addition, note that the following code produces the desired effect in ilasm:

.interfaceimpl type ITestInterface
.custom instance void Test1Attribute::.ctor() = ( 01 00 00 00 )
.interfaceimpl type ITestInterface
.custom instance void Test2Attribute::.ctor() = ( 01 00 00 00 )

But in that case, ildasm decompiles it to:

.interfaceimpl type ITestInterface
.custom instance void Test1Attribute::.ctor() = ( 01 00 00 00 ) 
.custom instance void Test2Attribute::.ctor() = ( 01 00 00 00 ) 

Which doesn't round-trip.

Reproduction Steps

Here is a test file, Test.il:

.assembly extern mscorlib
{
	.publickeytoken = ( b7 7a 5c 56 19 34 e0 89	)
	.ver 4:0:0:0
}
.assembly Test
{
	.hash algorithm 0x00008004 // SHA1
	.ver 1:0:0:0
}

.module Test.dll
.imagebase 0x10000000
.file alignment 0x00000200
.stackreserve 0x00100000
.subsystem 0x0003 // WindowsCui
.corflags 0x00000001 // ILOnly

.class private auto ansi '<Module>'
{
}

.class public auto ansi beforefieldinit TestType
    extends [mscorlib]System.Object
	implements ITestInterface
{
    .interfaceimpl type ITestInterface
    .custom instance void Test1Attribute::.ctor() = ( 01 00 00 00 )
    .custom instance void Test2Attribute::.ctor() = ( 01 00 00 00 )

    .method public hidebysig specialname rtspecialname
        instance void .ctor () cil managed
    {
        .maxstack 8

        IL_0000: ldarg.0
        IL_0001: call instance void [mscorlib]System.Object::.ctor()
        IL_0006: ret
    }
}

.class interface public auto ansi abstract ITestInterface
{
}

.class public auto ansi beforefieldinit Test1Attribute
    extends [mscorlib]System.Attribute
{
    .method public hidebysig specialname rtspecialname
        instance void .ctor () cil managed
    {
        .maxstack 8

        IL_0000: ldarg.0
        IL_0001: call instance void [mscorlib]System.Attribute::.ctor()
        IL_0006: ret
    }
}

.class public auto ansi beforefieldinit Test2Attribute
    extends [mscorlib]System.Attribute
{
    .method public hidebysig specialname rtspecialname
        instance void .ctor () cil managed
    {
        .maxstack 8

        IL_0000: ldarg.0
        IL_0001: call instance void [mscorlib]System.Attribute::.ctor()
        IL_0006: ret
    }
}

• Compile it with ilasm /DLL Test.il
• Decompile it with ildasm /OUT=TestOut.il Test.dll

Expected behavior

• Both Test1Attribute and Test2Attribute should be applied on the interface implementation (metadata table 09: InterfaceImpl)
• This shouldn't change when the code is round-tripped through ilasm/ildasm

Actual behavior

• Test1Attribute is applied on the interface implementation (metadata table 09: InterfaceImpl)
• Test2Attribute is applied on the type definition (metadata table 02: TypeDef)

Regression?

Not as far as I can tell.

Known Workarounds

Repeat .interfaceimpl type for each .custom instance to apply the custom attribute to the interface implementation.

No workaround for the round-trip inconsistency though.

Configuration

Tested with ilasm/ildasm from:

• the current main: 5ac3de1
• Microsoft.NETCore.ILAsm/Microsoft.NETCore.ILDAsm NuGet packages v6.0.0

(why are the v7.0.0 packages empty BTW?)

Other information

No response

Author:	ltrzesniewski
Assignees:	-
Labels:	area-ILTools-coreclr, untriaged
Milestone:	-

[JulieLeeMSFT]

cc @TIHan, PTAL.

[TIHan]

Will look at this tomorrow.