linux-kernel - Re: [PATCH 2/3] powerpc: fix build errors

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Message-ID: <20220225223319.GT614@gate.crashing.org>
Date:   Fri, 25 Feb 2022 16:33:19 -0600
From:   Segher Boessenkool <segher@...nel.crashing.org>
To:     Nicholas Piggin <npiggin@...il.com>
Cc:     Anders Roxell <anders.roxell@...aro.org>,
        Arnd Bergmann <arnd@...db.de>, linux-kernel@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org, mpe@...erman.id.au,
        stable@...r.kernel.org
Subject: Re: [PATCH 2/3] powerpc: fix build errors

On Fri, Feb 25, 2022 at 10:32:02AM +1000, Nicholas Piggin wrote:
> Excerpts from Segher Boessenkool's message of February 25, 2022 3:12 am:
> > On Thu, Feb 24, 2022 at 03:05:28PM +1000, Nicholas Piggin wrote:
> >> + * gcc 10 started to emit a .machine directive at the beginning of generated
> >> + * .s files, which overrides assembler -Wa,-m<cpu> options passed down.
> >> + * Unclear if this behaviour will be reverted.
> > 
> > It will not be reverted.  If you need a certain .machine for some asm
> > code, you should write just that!
> 
> It should be reverted because it breaks old binutils which did not have
> the workaround patch for this broken gcc behaviour. And it is just
> unnecessary because -m option can already be used to do the same thing.
> 
> Not that I expect gcc to revert it.

Nothing will happen if you do not file a bug report.  And do read the
bug reporting instructions first please.

> >> +#ifdef CONFIG_CC_IS_GCC
> >> +#if (GCC_VERSION >= 100000)
> >> +#if (CONFIG_AS_VERSION == 23800)
> >> +asm(".machine any");
> >> +#endif
> >> +#endif
> >> +#endif
> >> +#endif /* __ASSEMBLY__ */
> > 
> > Abusing toplevel asm like this is broken and you *will* end up with
> > unhappiness all around.
> 
> It actually unbreaks things and reduces my unhappiness.

It is broken.  You will need -fno-toplevel-reorder, and you really do
not want that, if you *can* use it in the kernel even.

> It's only done 
> for broken compiler versions and only where as does not have the 
> workaround for the breakage.

What compiler versions?  Please file a PR.


Segher