linux-kernel - Re: [PATCH v2 03/24] arm/cpu: Make sure arch_cpu_idle

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Message-ID: <Y+wEubLjgDQDIbSO@shell.armlinux.org.uk>
Date:   Tue, 14 Feb 2023 22:01:29 +0000
From:   "Russell King (Oracle)" <linux@...linux.org.uk>
To:     Josh Poimboeuf <jpoimboe@...nel.org>
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Subject: Re: [PATCH v2 03/24] arm/cpu: Make sure arch_cpu_idle_dead() doesn't
 return

On Tue, Feb 14, 2023 at 10:39:26AM -0800, Josh Poimboeuf wrote:
> On Tue, Feb 14, 2023 at 11:15:23AM +0000, Russell King (Oracle) wrote:
> > On Mon, Feb 13, 2023 at 11:05:37PM -0800, Josh Poimboeuf wrote:
> > > arch_cpu_idle_dead() doesn't return.  Make that more explicit with a
> > > BUG().
> > > 
> > > BUG() is preferable to unreachable() because BUG() is a more explicit
> > > failure mode and avoids undefined behavior like falling off the edge of
> > > the function into whatever code happens to be next.
> > 
> > This is silly. Just mark the function __noreturn and be done with it.
> > If the CPU ever executes code past the "b" instruction, it's already
> > really broken that the extra instructions that BUG() gives will be
> > meaningless.
> > 
> > This patch does nothing except add yet more bloat the kernel.
> > 
> > Sorry, but NAK.
> 
> Problem is, the compiler can't read inline asm.  So you'd get a 
> "'noreturn' function does return" warning.
> 
> We can do an unreachable() instead of a BUG() here if you prefer
> undefined behavior.

That's fine.

-- 
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