jextract for operating system API

[Maurizio Cimadamore]

On 23/08/2022 21:31, Manuel Bleichenbacher wrote:
> (1) The generated class _USB_NODE_CONNECTION_INFORMATION_EX cannot be 
> instanciated. The constructor throws the exception: 
> java.lang.UnsupportedOperationException: Invalid alignment 
> requirements for layout s16(DeviceAddress)
>
> This struct (like many USB descriptors) is packed with 16-bit integer 
> values on odd offsets. jextract insists on creating a layout with 
> strict alignment rules. So the generated layout 
> net.codecrete.usb.windows.gen.usbioctl._USB_NODE_CONNECTION_INFORMATION_EX#$struct$LAYOUT 
> fails, while the manually created layout 
> net.codecrete.usb.windows.USBIOCtl#USB_NODE_CONNECTION_INFORMATION_EX$Struct 
> works.

Seems like you have ran into this issue:

https://bugs.openjdk.org/browse/JDK-8259832


>
> (2) The struct _SP_DEVICE_INTERFACE_DETAIL_DATA_W isn't usable. In C, 
> it looks like this:
>
> typedef struct _SP_DEVICE_INTERFACE_DETAIL_DATA_W {
>   DWORD cbSize;
>   WCHAR DevicePath[ANYSIZE_ARRAY];
> } SP_DEVICE_INTERFACE_DETAIL_DATA_W, *PSP_DEVICE_INTERFACE_DETAIL_DATA_W;

In general, there's not much that can be done for variable-length arrays 
- but perhaps, in the idiomatic case where the array occurs as the last 
field of a struct, the allocate methods for the struct could take the 
array size and allocate a segment that is big enough. We could also emit 
(unsafe) accessors to access elements of the VLA.

Filed an issue to keep track of this:

https://bugs.openjdk.org/browse/CODETOOLS-7903283


Thanks
Maurizio