linux-kernel - Re: [RFC][PATCH] x86: Make x32 syscall support conditional on a kernel parameter

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Date:	Thu, 06 Nov 2014 16:25:13 +0000
From:	Ben Hutchings <ben@...adent.org.uk>
To:	Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:	the arch/x86 maintainers <x86@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [RFC][PATCH] x86: Make x32 syscall support conditional on a
 kernel parameter

On Thu, 2014-11-06 at 09:02 +0100, Geert Uytterhoeven wrote:
> On Thu, Nov 6, 2014 at 4:53 AM, Ben Hutchings <ben@...adent.org.uk> wrote:
[...]
> > diff --git a/arch/x86/kernel/syscall_64.c b/arch/x86/kernel/syscall_64.c
> > index 4ac730b..7a6e66f 100644
> > --- a/arch/x86/kernel/syscall_64.c
> > +++ b/arch/x86/kernel/syscall_64.c
> 
> > +static int __init x32_enable(void)
> > +{
> > +       BUG_ON(system_call_fast_compare_end - system_call_fast_compare != 10);
> > +       BUG_ON(system_call_trace_compare_end - system_call_trace_compare != 10);
> > +       BUG_ON(system_call_mask_compare_end - system_call_mask_compare != 10);
> 
> BUILD_BUG_ON

No, these can't be evaluated at compile time because the symbols are
external.

> > +
> > +       if (x32_enabled) {
> > +               text_poke_early(system_call_fast_compare,
> > +                               system_call_mask_compare, 10);
> > +               text_poke_early(system_call_trace_compare,
> > +                               system_call_mask_compare, 10);
> > +#ifdef CONFIG_X86_X32_DISABLED
> > +               pr_info("Enabled x32 syscalls\n");
> > +#endif
> 
> I don't think it hurts to print this unconditionally.
[...]

It seemed like it would be unnecessary noise in an x32-only system.

Ben.

-- 
Ben Hutchings
Beware of programmers who carry screwdrivers. - Leonard Brandwein

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