NativeAOT: Memset/Memcpy helpers don't throw NRE

[EgorBo]

Compile the following program and run:

static unsafe void Main(string[] args)
{
    Unsafe.InitBlock(null, 0, 1000);
}

CoreCLR:

Unhandled exception. System.NullReferenceException: Object reference not set to an instance of an object.

NativeAOT:

no exception, exits.

I assume this is what these comments mean:

runtime/src/coreclr/tools/aot/ILCompiler.Compiler/Compiler/JitHelper.cs

Lines 118 to 123 in 3e55167

	case ReadyToRunHelper.MemCpy:
	mangledName = "memcpy"; // TODO: Null reference handling
	break;
	case ReadyToRunHelper.MemSet:
	mangledName = "memset"; // TODO: Null reference handling
	break;

so I decided to file a tracking issue.

(while CoreCLR wraps memset/memcpy calls into non-inlineable/without tail calls helpers)

[ghost]

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Issue Details

---

Compile the following program and run:

static unsafe void Main(string[] args)
{
    Unsafe.InitBlock(null, 0, 1000);
}

CoreCLR:

Unhandled exception. System.NullReferenceException: Object reference not set to an instance of an object.

NativeAOT:

no exception, exits.

I assume this is what these comments mean:

runtime/src/coreclr/tools/aot/ILCompiler.Compiler/Compiler/JitHelper.cs

Lines 118 to 123 in 3e55167

	case ReadyToRunHelper.MemCpy:
	mangledName = "memcpy"; // TODO: Null reference handling
	break;
	case ReadyToRunHelper.MemSet:
	mangledName = "memset"; // TODO: Null reference handling
	break;

(while CoreCLR wraps memset/memcpy calls into non-inlineable/without tail calls helpers)

Author:	EgorBo
Assignees:	-
Labels:	area-NativeAOT-coreclr
Milestone:	-

[filipnavara]

This can happen when unboxing tries to use memcpy:

struct X { int a, b, c, d, e, f, g, h, ... };
X? x = null;
object box = (object)x;
int val = (X)box;

Instead of getting a NullReferenceException it results in a crash inside memcpy with null dereference that is practically undebuggable (no stack trace available due to native code optimizations).