[NativeAOT/ARM] NativePrimitiveDecoder generates unaligned accesses with VLDR instruction

[filipnavara]

Code:

runtime/src/coreclr/tools/Common/Internal/NativeFormat/NativeFormatReader.Primitives.cs

Lines 17 to 43 in 2361c00

	public static byte ReadUInt8(ref byte* stream)
	{
	byte result = *(stream); // Assumes little endian and unaligned access
	stream++;
	return result;
	}
	public static ushort ReadUInt16(ref byte* stream)
	{
	ushort result = *(ushort*)(stream); // Assumes little endian and unaligned access
	stream += 2;
	return result;
	}
	public static uint ReadUInt32(ref byte* stream)
	{
	uint result = *(uint*)(stream); // Assumes little endian and unaligned access
	stream += 4;
	return result;
	}
	public static ulong ReadUInt64(ref byte* stream)
	{
	ulong result = *(ulong*)(stream); // Assumes little endian and unaligned access
	stream += 8;
	return result;
	}

Crash at runtime:

* thread #1, name = 'System.Runtime.', stop reason = signal SIGBUS
  * frame #0: 0x0204ba16 System.Runtime.Tests`Internal.Metadata.NativeFormat.MetadataReader__GetConstantSingleValue(this=0xf49a9454, handle=(_value = 403231906)) at NativeFormatReaderGen.cs:10446
    frame #1: 0x0203cf36 System.Runtime.Tests`System.Reflection.Runtime.General.NativeFormatMetadataReaderExtensions__ParseConstantNumericValue(handle=<unavailable>, reader=<unavailable>) at MetadataReaderExtensions.NativeFormat.cs:278
    frame #2: 0x0203d050 System.Runtime.Tests`System.Reflection.Runtime.General.NativeFormatMetadataReaderExtensions__TryParseConstantValue(handle=<unavailable>, reader=<unavailable>, value=0xf50eb2f0) at MetadataReaderExtensions.NativeFormat.cs:303
    frame #3: 0x0203d4e6 System.Runtime.Tests`System.Reflection.Runtime.General.NativeFormatMetadataReaderExtensions__TryParseConstantArray(handle=<unavailable>, reader=0xf49a9454, exception=0xf03fe26c) at MetadataReaderExtensions.NativeFormat.cs:405
    frame #4: 0x0203d0da System.Runtime.Tests`System.Reflection.Runtime.General.NativeFormatMetadataReaderExtensions__TryParseConstantValue(handle=<unavailable>, reader=<unavailable>, value=0xf03fe2c8) at MetadataReaderExtensions.NativeFormat.cs:327
    frame #5: 0x02041922 System.Runtime.Tests`System.Reflection.Runtime.CustomAttributes.NativeFormat.NativeFormatCustomAttributeData__GetConstructorArguments(this=0xf50eb1b0, throwIfMissingMetadata=true) at NativeFormatCustomAttributeData.cs:132
    frame #6: 0x020405a4 System.Runtime.Tests`System.Reflection.Runtime.CustomAttributes.RuntimeCustomAttributeData__get_ConstructorArguments(this=<unavailable>) at RuntimeCustomAttributeData.cs:24
    ...

  0x204ba16 <+53>: vldr   s8, [r3]

        r3 = 0x00a88312  System.Runtime.Tests`__embedded_metadata + 578722

VLDR is not handled by the kernel unalignment traps (ref: raspberrypi/linux#3099) and it doesn't natively support unaligned access.

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Issue Details

---

Code:

runtime/src/coreclr/tools/Common/Internal/NativeFormat/NativeFormatReader.Primitives.cs

Lines 17 to 43 in 2361c00

	public static byte ReadUInt8(ref byte* stream)
	{
	byte result = *(stream); // Assumes little endian and unaligned access
	stream++;
	return result;
	}
	public static ushort ReadUInt16(ref byte* stream)
	{
	ushort result = *(ushort*)(stream); // Assumes little endian and unaligned access
	stream += 2;
	return result;
	}
	public static uint ReadUInt32(ref byte* stream)
	{
	uint result = *(uint*)(stream); // Assumes little endian and unaligned access
	stream += 4;
	return result;
	}
	public static ulong ReadUInt64(ref byte* stream)
	{
	ulong result = *(ulong*)(stream); // Assumes little endian and unaligned access
	stream += 8;
	return result;
	}

Crash at runtime:

* thread #1, name = 'System.Runtime.', stop reason = signal SIGBUS
  * frame #0: 0x0204ba16 System.Runtime.Tests`Internal.Metadata.NativeFormat.MetadataReader__GetConstantSingleValue(this=0xf49a9454, handle=(_value = 403231906)) at NativeFormatReaderGen.cs:10446
    frame #1: 0x0203cf36 System.Runtime.Tests`System.Reflection.Runtime.General.NativeFormatMetadataReaderExtensions__ParseConstantNumericValue(handle=<unavailable>, reader=<unavailable>) at MetadataReaderExtensions.NativeFormat.cs:278
    frame #2: 0x0203d050 System.Runtime.Tests`System.Reflection.Runtime.General.NativeFormatMetadataReaderExtensions__TryParseConstantValue(handle=<unavailable>, reader=<unavailable>, value=0xf50eb2f0) at MetadataReaderExtensions.NativeFormat.cs:303
    frame #3: 0x0203d4e6 System.Runtime.Tests`System.Reflection.Runtime.General.NativeFormatMetadataReaderExtensions__TryParseConstantArray(handle=<unavailable>, reader=0xf49a9454, exception=0xf03fe26c) at MetadataReaderExtensions.NativeFormat.cs:405
    frame #4: 0x0203d0da System.Runtime.Tests`System.Reflection.Runtime.General.NativeFormatMetadataReaderExtensions__TryParseConstantValue(handle=<unavailable>, reader=<unavailable>, value=0xf03fe2c8) at MetadataReaderExtensions.NativeFormat.cs:327
    frame #5: 0x02041922 System.Runtime.Tests`System.Reflection.Runtime.CustomAttributes.NativeFormat.NativeFormatCustomAttributeData__GetConstructorArguments(this=0xf50eb1b0, throwIfMissingMetadata=true) at NativeFormatCustomAttributeData.cs:132
    frame #6: 0x020405a4 System.Runtime.Tests`System.Reflection.Runtime.CustomAttributes.RuntimeCustomAttributeData__get_ConstructorArguments(this=<unavailable>) at RuntimeCustomAttributeData.cs:24
    ...

  0x204ba16 <+53>: vldr   s8, [r3]

        r3 = 0x00a88312  System.Runtime.Tests`__embedded_metadata + 578722

VLDR is not handled by the kernel unalignment traps (ref: raspberrypi/linux#3099).

Author:	filipnavara
Assignees:	-
Labels:	arch-arm32, area-NativeAOT-coreclr
Milestone:	-

[filipnavara]

This actually looks like a RyuJIT issue. There are code paths in the JIT that handle this for field access (1, 2), so it feels like the JIT should also not try to optimize this.