0xc0000005 exception when calling static functions

[jagobagascon]

          I encountered a similar issue with a very simple test:

https://github.com/balazsgrill/winrt-go/blob/main/storage_test.go

However I doubt that this time it's caused by the GC as it still fails when I disable it

Exception 0xc0000005 0x1 0x50 0x7ffa3fa96d43
PC=0x7ffa3fa96d43

Originally posted by @balazsgrill in https://github.com/saltosystems/winrt-go/issues/94#issuecomment-2294852767

[jagobagascon]

@balazsgrill I did a quick test and it seems that we are not correctly calling static methods.

We are always passing a first NULL parameter:

hr, _, _ := syscall.SyscallN(
    v.VTable().StorageFolderGetFolderFromPathAsync,
    uintptr(0),                    // this is a static func, so there's no this
    uintptr(pathHStr),             // in string
    uintptr(unsafe.Pointer(&out)), // out foundation.IAsyncOperation
)

And even though I can't find anything in the runtime docs related to this (https://learn.microsoft.com/en-us/uwp/winrt-cref/winrt-type-system), it looks like the Rust implementation always passes a pointer to the current parent interface.

So I replaced the first 0 (null) parameter with a pointer to the iStorageFolderStatics instance and it now works:

v := (*iStorageFolderStatics)(unsafe.Pointer(inspectable))
hr, _, _ := syscall.SyscallN(
    v.VTable().StorageFolderGetFolderFromPathAsync,
    uintptr(unsafe.Pointer(v)),    // this is a static func, but we are adding iStorageFolderStatics as "this"
    uintptr(pathHStr),             // in string
    uintptr(unsafe.Pointer(&out)), // out foundation.IAsyncOperation
)

[jagobagascon]

Passing NULL or an instance pointer seems to have zero impact on most static methods (Buffer.Create for example works in both cases), but that's not the case for StorageFolder.GetFolderFromPathAsync.

[balazsgrill]

Thank you for investigating this. It took some time for me to figure out how async operations are working but with this change the test runs successfully https://github.com/balazsgrill/winrt-go/commit/7cb59d11d218986ed025821ae17cbbfe865e86a0

[balazsgrill]

it looks like the Rust implementation always passes a pointer to the current parent interface.

I suppose then modifying the template to always generate "this" is the appropriate solution (https://github.com/balazsgrill/winrt-go/commit/ed5621d1dfca9e0d8ab08e1830426c6455669507#diff-15f31657e55dbae4403357fb11617c4118c705bf171961ef5d9ae9635fbc2c14)

[jagobagascon]

I suppose then modifying the template to always generate "this" is the appropriate solution

Probably. It still bothers me that most of the code just works without adding it. And I cannot find any mention to it in the docs. So I would like to thoroughly test this with the https://github.com/tinygo-org/bluetooth library before adding any PR.