On Thu, Mar 9, 2023 at 9:24 PM Faith Ekstrand faith.ekstrand@collabora.com wrote:
On Thu, 2023-03-09 at 15:04 +0900, Asahi Lina wrote:
On 08/03/2023 02.34, Björn Roy Baron wrote:
// SAFETY: This is just the ioctlargument, which hopefully has the right type
// (we've done our best checking thesize).
In the rust tree there is the ReadableFromBytes [1] trait which indicates that it is safe to read arbitrary bytes into the type. Maybe you could add it as bound on the argument type when it lands in rust-next? This way you can't end up with for example a struct containing a bool with the byte value 2, which is UB.
There's actually a much bigger story here, because that trait isn't really very useful without a way to auto-derive it. I need the same kind of guarantee for all the GPU firmware structs...
There's one using only declarative macros [1] and one using proc macros [2]. And then, since ioctl arguments are declared in C UAPI header files, we need a way to be able to derive those traits for them... which I guess means bindgen changes?
It'd be cool to be able to auto-verify that uAPI structs are all tightly packed and use the right subset of types. Maybe not possible this iteration but it'd be cool to see in future. I'd like to see it for C as well, ideally.
~Faith
I'm sure that with a macro you could verify that a struct definition doesn't contain any gaps, just not sure on how one would enforce that. Could add a trait which can only be implemented through a proc_macro? Maybe we can have a proc_macro ensuring no gaps? Would be cool tech to have indeed.