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

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Message-ID: <20230214183926.46trlpdror3v5sk5@treble>
Date:   Tue, 14 Feb 2023 10:39:26 -0800
From:   Josh Poimboeuf <jpoimboe@...nel.org>
To:     "Russell King (Oracle)" <linux@...linux.org.uk>
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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 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.

-- 
Josh