linux-kernel - Re: [PATCH RESEND v2 00/19] random: Resolve circular include dependency and include <linux/percpu.h>

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Message-ID: <Zt-U0opo2EW8LSRJ@zx2c4.com>
Date: Tue, 10 Sep 2024 02:37:38 +0200
From: "Jason A. Donenfeld" <Jason@...c4.com>
To: Uros Bizjak <ubizjak@...il.com>
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Subject: Re: [PATCH RESEND v2 00/19] random: Resolve circular include
 dependency and include <linux/percpu.h>

Hi Uros,

On Mon, Sep 09, 2024 at 09:30:06PM +0200, Uros Bizjak wrote:
> Besides GCC, clang can define various named address space via
> address_space attribute:
> 
> --cut here--
> #define __as(N) __attribute__((address_space(N)))
> 
> void *foo(void __as(1) *x) { return x; }         // error
> 
> void *bar(void __as(1) *x) { return (void *)x; } // fine
> --cut here--
> 
> When compiling this, the compiler returns:
> 
> clang-as.c:3:37: error: returning '__as(1) void *' from a function
> with result type 'void *' changes address space of pointer

Super cool. Looking forward to having it all wired up and the bugs we'll
find with it. 

> I think that the best approach is to target this patchset for linux
> 6.13 via random.git tree. I will prepare a v3 after 6.12rc1, so when
> committed to random.git, the patchset will be able to spend some time
> in linux-next. This way, there will be plenty of time for CI robots to
> do additional checks also for some less popular targets (although
> individual patches are dead simple, removing these kinds of "legacy"
> includes can be tricky), and I will also be able to collect Acked-by:s
> in the meantime.
> 
> While the patchset is an improvement by itself, its inclusion is not
> time sensitive. The follow up percpu named address checking
> functionality requires a very recent feature (__typeof_unqual__
> keyword), which is only supported in recent compilers (gcc-14 and
> clang-20). Besides compiler support, sparse doesn't know about
> __typeof_unqual__, resulting in broken type tracing and hundreds of
> sparse errors with C=1 due to unknown keyword.
> 
> So, I think we are not in a hurry and can take the slow and safe path.

Okay, sure, that sounds good to me. I'll keep my eyes open for v3
in a few weeks then.

Jason