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Date: Thu, 14 Jul 2011 15:31:13 -0700
From: Andrew Morton <akpm@linux-foundation.org>
To: Mike Waychison <mikew@google.com>
Cc: Greg Kroah-Hartman <gregkh@suse.de>, Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>,
        x86@kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 2/2] x86: Allow disabling of sys_iopl, sys_ioperm
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On Thu, 14 Jul 2011 13:34:53 -0700
Mike Waychison <mikew@google.com> wrote:

> --- a/arch/x86/kernel/ioport.c
> +++ b/arch/x86/kernel/ioport.c
> @@ -17,6 +17,7 @@
>  #include <linux/bitmap.h>
>  #include <asm/syscalls.h>
>  
> +#ifdef CONFIG_X86_SYS_IOPL
>  /*
>   * this changes the io permissions bitmap in the current task.
>   */
> @@ -111,3 +112,14 @@ long sys_iopl(unsigned int level, struct pt_regs *regs)
>  
>  	return 0;
>  }
> +
> +#else /* CONFIG_X86_SYS_IOPL */
> +
> +asmlinkage long sys_ioperm(unsigned long from, unsigned long num, int turn_on) {
> +	return -ENOSYS;
> +}
> +
> +long sys_iopl(unsigned int level, struct pt_regs *regs) {
> +	return -ENOSYS;
> +}
> +#endif /* CONFIG_X86_SYS_IOPL */

sys_iopl() is missing asmlinkage.

It would be far more conventional to use cond_syscall().  Perhaps by
adding a CONFIG_X86 area into kernel/sys_ni.c

fyi, I'm offering special deals on checkpatch.pl site licenses this month.