When interfacing with C with other languages, it is often necessary to write wrapper functions to access C structs because there are no general (and free) tools available which can generate structure layout information from C sources.
For example, suppose that I want to write Ada code which uses the poll(2) from POSIX. POSIX only guarantees that the following fields are available in struct pollfd: | int fd The following descriptor being polled. | short events The input event flags (see below). | short revents The output event flags (see below). Additional members are permitted, and the fields can be order. In order to create a portable Ada interface, I have to write a short C program which uses sizeof and offsetof to extract the structure layout. In theory, it is possible to create compile-time-only tests suitable for cross-compilation (compile-time constant expressions, invalid zero-length arrays, and a binary search), but this is rather messy. This is probably one of the reason why the GNAT run-time library currently uses manually translated record definitions, which reduces its portability. Are there any objections to exporting structure layout from GCC, in a format which can be parsed in a straightforward manner? Such a patch could be used as a GPL circumvention device, but I'm not sure how relevant this is in practice because GCC follows published ABIs, so a clean-room reimplementation would be straightforward (IOW, there isn't much to lose for us because our competetive edge is pretty minimal).
