Compiling Rust with GCC: an update

Posted Sep 11, 2022 0:33 UTC (Sun) by khim (subscriber, #9252)
In reply to: Compiling Rust with GCC: an update by tialaramex
Parent article: Compiling Rust with GCC: an update

> Today you have to be more careful, nobody warned you about this, beyond the general warning that what you were doing was "unsafe" but what you were doing might stop working. On some platforms. Or maybe not. You have to either obey Strict Provenance, or you need to say OK, I can't meet these requirements, I opt out of strict provenance and I'll take my chances with this PNVI exposure stuff, and in both cases that has consequences I won't summarise here and it could change.

But how can multiple implementations help there? C and C++ do have multiple implementation, the do have ISO Standard (many ones, actually) yet to this very day nobody knows what can or can not be done with pointers.

I think this is the last attempt which tried to clarify the issue (and proposal to, you know, make compilers which actually obey the standard as published was explicitly rejected).

At least Rust developers never claimed that they have a normative documentation which explains how unsafe is supposed to work.

C and C++ pretend that they do have such documentation and there are even people who claim that Rust is deficient because of that!

IMNSHO informative documentation is better that something which claims to be a normative documentation which you couldn't use as such.

At least if documentation is informative you know you couldn't use it as a guide.

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Compiling Rust with GCC: an update

Posted Sep 11, 2022 9:20 UTC (Sun) by tialaramex (subscriber, #21167) [Link]

https://open-std.org/JTC1/SC22/WG14/www/docs/n3005.pdf is the current state of TS 6010, the draft Technical Specification which is what happened to N2676

So, modulo crazy ISO problems, the C23 standard per se won't mandate this roughly PNVI-address exposed model, but there will be an ISO document separately specifying how this would work. The standard is... rough. But there is limited enthusiasm for figuring out all the fine details while it remains unclear if everybody will even implement it. This only starts to make sense once at least two major compilers (e.g. MSVC and GCC) implement it.

With TS6010 you get most of the optimisations people expect in a modern compiler, and which of course Rust is doing, but you can do a XOR doubly linked list in C, as one example of stunt pointer manipulation that some people still think is a good idea. Of course some optimisations are given up in your doubly linked list code to make this work, but you don't feel that loss in unrelated code.