linux-kernel - Re: [PATCH AUTOSEL 6.1 04/13] rust: arch/um: Disable FP/SIMD instruction to match x86

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Date:   Thu, 27 Apr 2023 10:30:52 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     SeongJae Park <sj@...nel.org>
Cc:     Sasha Levin <sashal@...nel.org>, linux-kernel@...r.kernel.org,
        stable@...r.kernel.org, David Gow <davidgow@...gle.com>,
        Sergio González Collado 
        <sergio.collado@...il.com>, Richard Weinberger <richard@....at>,
        tglx@...utronix.de, mingo@...hat.com, hpa@...or.com, x86@...nel.org
Subject: Re: [PATCH AUTOSEL 6.1 04/13] rust: arch/um: Disable FP/SIMD
 instruction to match x86

On Tue, Apr 25, 2023 at 12:01:18AM +0000, SeongJae Park wrote:
> Hello Sasha and Greg,
> 
> 
> On Tue, 14 Mar 2023 08:43:16 -0400 Sasha Levin <sashal@...nel.org> wrote:
> 
> > From: David Gow <davidgow@...gle.com>
> > 
> > [ Upstream commit 8849818679478933dd1d9718741f4daa3f4e8b86 ]
> > 
> > The kernel disables all SSE and similar FP/SIMD instructions on
> > x86-based architectures (partly because we shouldn't be using floats in
> > the kernel, and partly to avoid the need for stack alignment, see:
> > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=53383 )
> > 
> > UML does not do the same thing, which isn't in itself a problem, but
> > does add to the list of differences between UML and "normal" x86 builds.
> > 
> > In addition, there was a crash bug with LLVM < 15 / rustc < 1.65 when
> > building with SSE, so disabling it fixes rust builds with earlier
> > compiler versions, see:
> > https://github.com/Rust-for-Linux/linux/pull/881
> > 
> > Signed-off-by: David Gow <davidgow@...gle.com>
> > Reviewed-by: Sergio González Collado <sergio.collado@...il.com>
> > Signed-off-by: Richard Weinberger <richard@....at>
> > Signed-off-by: Sasha Levin <sashal@...nel.org>
> 
> There is a followup fix of this patch that merged into the mainline by commit
> a3046a618a28 ("um: Only disable SSE on clang to work around old GCC bugs"), but
> it has not added to 6.1.y so far.  Without it, compiling on some setup using an
> old version of gcc fails, as the followup is also mentioning.  I also confirmed
> the issue can be reproduced on latest 6.1.y.
> 
> Could you please add the followup fix to 6.1.y?  I confirmed the commit can be
> cleanly cherry-picked on latest 6.1.y, and fixes the issue as expected.

Now queued up, thanks.

greg k-h