Re: [PATCH 3/3] rust: add tracepoint support

[Boqun Feng]

On Thu, Jun 06, 2024 at 09:29:51PM +0200, Peter Zijlstra wrote:
> On Thu, Jun 06, 2024 at 12:00:36PM -0700, Boqun Feng wrote:
> > On Thu, Jun 06, 2024 at 07:35:44PM +0200, Peter Zijlstra wrote:
> > > On Thu, Jun 06, 2024 at 08:49:06AM -0700, Boqun Feng wrote:
> > > 
> > > > Long-term plan is to 1) compile the C helpers in some IR and 2) inline
> > > > the helpers with Rust in IR-level, as what Gary has:
> > > > 
> > > > 	https://lore.kernel.org/rust-for-linux/20240529202817.3641974-1-gary@xxxxxxxxxxx/
> > > 
> > > Urgh, that still needs us to maintain that silly list of helpers :-/
> > > 
> > 
> > But it's an improvement from the current stage, right? ;-)
> 
> Somewhat, but only marginal.
> 
> > > Can't we pretty please have clang parse the actual header files into IR
> > > and munge that into rust? So that we don't get to manually duplicate
> > > everything+dog.
> > 
> > That won't always work, because some of our kernel APIs are defined as
> > macros, and I don't think it's a trivial job to generate a macro
> > definition to a function definition so that it can be translated to
> > something in IR. We will have to do the macro -> function mapping
> > ourselves somewhere, if we want to inline the API across languages.
> 
> We can try and see how far we can get with moving a bunch of stuff into
> inlines. There's quite a bit of simple CPP that could be inlines or
> const objects I suppose.
> 

We can, but I'd first stick with what we have, improve it and make it
stable until we go to the next stage. Plus, there's benefit of keeping
an explicit helper list: it's clear what APIs are called by Rust, and
moreover, it's easier to modify the helpers if you were to change an
API, other than chasing where Rust code calls it. (Don't make me wrong,
I'm happy if you want to do that ;-))

Regards,
Boqun

> Things like the tracepoints are of course glorious CPP abuse and are
> never going to work.
> 
> But perhaps you can have an explicit 'eval-CPP on this here' construct
> or whatnot. If I squit I see this paste! thingy (WTF's up with that !
> operator?) to munge function names in the static_call thing. So
> something like apply CPP from over there on this here can also be done
> :-)