How to get layout of managed object conveniently?

[huoyaoyuan]

During development of vm code, it's often necessary to confirm object layout. Currently I'm relying on checks in corelib.h, which is inconvenient and can miss other architectures.
Is there any tooling to get layout of each field, or is there any doc to explain the layout rule?
VS17.8 is adding object size and alignment hint in IntelliSense for C++.

@jkotas any advise?

[jkotas]

We have been trying to minimize the number of mirrored structures and keep the data structures that need to be mirrored simple. corelib.h is about 2x smaller compared to what it was in .NET Core 1.0 days.

There is no silver bullet for computing the matching layouts for complex data structures. Both the managed and unmanaged field layout algorithms are architecture specific.

[jkotas]

there any doc to explain the layout rule?

The sequential field layout is simple. The auto layout - that everything that contains GC references uses - is reordering the fields to maximize packing (primitive fields of the same size are reordered together) and improve GC reference locality (all GC references are reordered together).

[DaZombieKiller]

all GC references are reordered together

Is there any particular order that the algorithm currently stores GC references in after they have been grouped? Do they retain the declaration order or something else?

[jkotas]

They retain the declaration order.

[huoyaoyuan]

I'm confused with the reorder of unmanaged fields with different sizes right now. Namely, an object with object, object, IntPtr, IntPtr, int, bool, bool.

[MichalPetryka]

Namely, an object with object, object, IntPtr, IntPtr, int, bool, bool.

https://sharplab.io/#v2:EYLgxg9gTgpgtADwGwBYA0AXEUCuA7AHwAEAmARgFgAoagYjxwBtGBDYRmAAgBMBLAZzYdq1AJJ5+ABxhgMAOgASMFpIAUeGAHdOAFRj8MqgJRGA3CKpEAzJ1K79GagG9qnN7ZsRgAKxkZOLJwAvJwamsbmVO4enF6+spzAwaFaEa7u1pziGAAKGFCcYMlkkdGZ2XkF3MkkpRk2vHj+XCFWdW6ZwBAQjJwAZsl9LIz8MO0xXT2cAObJ+Thj1AC+QA===

[huoyaoyuan]

@MichalPetryka good solution here.
There is also dumpobj command for WinDbg, just no convenient way within VS. Anyway, using diagnostic tools to get the layout should be expected way.

[Korporal]

@huoyaoyuan

During development of vm code, it's often necessary to confirm object layout. Currently I'm relying on checks in corelib.h, which is inconvenient and can miss other architectures. Is there any tooling to get layout of each field, or is there any doc to explain the layout rule? VS17.8 is adding object size and alignment hint in IntelliSense for C++.

@jkotas any advise?

You can create custom IL to enumerate all fields and then get their offsets and sizes, that's something done here for example:

#100487 (comment)

If you copy that code and play around with it, you'll see it works OK for ref or value types (the code isn't as good as it could be, no pinning and so on but you get the idea).

[huoyaoyuan]

Well this question is specific for CoreLib. If things are getting wrong, the CLR just refuses to execute any managed code.
I can just copy the data structure and execute in another project instead.