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unsafe struct fails with primitive field only when at the end of the sequence #105064
Description
I have a project (tested with .NET6 and .NET8) with AllowUnsafeBlocks.
I then have a struct containing 2 fixed int arrays and a regular int.
The first two structs (SampleDataMemory_Works1 and SampleDataMemory_Works2) do work, the third one (SampleDataMemory_Crash1) crashes with System.TypeLoadException: Could not find or load a type. (0x80131522).
class and structs
public unsafe struct SampleDataMemory_Works1
{
public int index;
public fixed int processComplete[ClassTest.MAX_SAMPLE_BUFFER_SIZE];
public fixed int data[ClassTest.MAX_SAMPLE_BUFFER_SIZE];
};
[StructLayout(LayoutKind.Sequential, Pack = 1)]
public unsafe struct SampleDataMemory_Works2
{
public fixed int processComplete[ClassTest.MAX_SAMPLE_BUFFER_SIZE];
public int index;
public fixed int data[ClassTest.MAX_SAMPLE_BUFFER_SIZE];
};
[StructLayout(LayoutKind.Sequential, Pack = 1)]
public unsafe struct SampleDataMemory_Crash1
{
public fixed int processComplete[ClassTest.MAX_SAMPLE_BUFFER_SIZE];
public fixed int data[ClassTest.MAX_SAMPLE_BUFFER_SIZE];
public int index;
};
public class ClassTest
{
public const int MAX_SAMPLE_BUFFER_SIZE = 20000000;
public static int GetSizeWorks1()
{
return Marshal.SizeOf<SampleDataMemory_Works1>();
}
public static int GetSizeWorks2()
{
return Marshal.SizeOf<SampleDataMemory_Works2>();
}
public static int GetSizeCrash1()
{
return Marshal.SizeOf<SampleDataMemory_Crash1>();
}
}
csproj
<Project Sdk="Microsoft.NET.Sdk">
<PropertyGroup>
<TargetFramework>net6.0</TargetFramework>
<ImplicitUsings>enable</ImplicitUsings>
<Nullable>enable</Nullable>
<AllowUnsafeBlocks>true</AllowUnsafeBlocks>
</PropertyGroup>
</Project>
As you can see all structs have the same size, the only thing different is the position of the the index property, all types are the same.
I wonder why we get this behaviour, assuming the size should be the same.
I can easily increase the size of the arrays even more and it still works for the first two structs, but a single int after the two fixed arrays makes it crash.
Activity
huoyaoyuan commentedon Jul 18, 2024
It's likely because field offset exceeding the limit. Add a more
public fixed int processComplete2[ClassTest.MAX_SAMPLE_BUFFER_SIZE];at the front ofSampleDataMemory_Works2, or doubling the size ofMAX_SAMPLE_BUFFER_SIZEwill both result inTypeLoadException.#95193 (comment) indicates that the maximum field offset is around 2^27.
20000000 * sizeof(int)is more than 2^26.fanyang-mono commentedon Jul 18, 2024
This looks like a similar issue to #97412
However, I would expect SampleDataMemory_Works1 and SampleDataMemory_Works2 trigger the TypeLoadException as well. I will look into it.
luislhg commentedon Jul 18, 2024
I actually tried setting
MAX_SAMPLE_BUFFER_SIZEto1 << 25(33.554.432) and it still fails when the field is after. If the field is positioned before then it works.Below are new examples showing the real boundaries I found:
As long as I declare my second field BEFORE
(1 << 25) - 4I can declare whatever I want (int, bool or even another huge array as you can see in SampleDataMemory_Works5)steveisok commentedon Aug 8, 2024
As noted in #104393 (comment), we want to have the change apply for all runtimes. This will likely to through in .NET 10 as a result.
steveisok commentedon Aug 8, 2024
@MichalStrehovsky since nativeaot is the only runtime left, I'm assigning this issue to you.
MichalStrehovsky commentedon Aug 8, 2024
Could you clarify what work you expect me to do? This is a customer running into this limit in the CoreCLR VM:
runtime/src/coreclr/vm/field.h
Lines 14 to 20 in 61b0020
Managed type system (as used by crossgen2 or ILC) doesn't have such limit. I don't see #104393 doing anything for this. There was a suggestion from Jan to print a better exception message but even that wasn't done in that PR (and could be done in a different PR too, since it's unrelated).
steveisok commentedon Aug 8, 2024
My bad, I got crossed up between this and #97412