linux-kernel - Re: [PATCH] x86/signal: fix restart

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Message-ID: <20151213034437.GA2392@altlinux.org>
Date:	Sun, 13 Dec 2015 06:44:40 +0300
From:	"Dmitry V. Levin" <ldv@...linux.org>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	X86 ML <x86@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Elvira Khabirova <lineprinter0@...il.com>
Subject: Re: [PATCH] x86/signal: fix restart_syscall number for x32 tasks

On Mon, Dec 07, 2015 at 03:22:06PM -0800, Andy Lutomirski wrote:
> [not real reply because I'm using a bad internet connection right now
> and I'm not set up with my usual Gmane reply hack right now]
> 
> The new code is (whitespace-damaged):
> 
> static inline unsigned long get_nr_restart_syscall(const struct pt_regs *regs)
> {
> #if defined(CONFIG_X86_32) || !defined(CONFIG_X86_64)
>  return __NR_restart_syscall;
> #else /* !CONFIG_X86_32 && CONFIG_X86_64 */
>  return test_thread_flag(TIF_IA32) ? __NR_ia32_restart_syscall :
>  __NR_restart_syscall | (regs->orig_ax & __X32_SYSCALL_BIT);
> #endif /* CONFIG_X86_32 || !CONFIG_X86_64 */
> }
> 
> This is IMO awful.  This use of TIF_IA32 is wrong, and this is
> otherwise gross.  Can we do it for real:
> 
> if (is_ia32_task())
>   return __NR_ia32_restart_syscall;
> else
>   return __NR_restart_syscall | (regs->orig_ax & __X32_SYSCALL_BIT);
> /* preserve x32 bit */
> 
> I'd send the patch myself, but you apparently have a good test case
> for this, and I don't.

Unfortunately, this won't compile on CONFIG_X86_32 because
__NR_ia32_restart_syscall is defined for CONFIG_X86_64 only.

Something like this should work:

static inline unsigned long get_nr_restart_syscall(const struct pt_regs *regs)
{
#ifdef CONFIG_X86_64
	if (is_ia32_task())
		return __NR_ia32_restart_syscall;
# ifdef CONFIG_X86_X32_ABI
	if (regs->orig_ax & __X32_SYSCALL_BIT)
		return __NR_restart_syscall | __X32_SYSCALL_BIT;
# endif
#endif
	return __NR_restart_syscall;
}

I don't see any way to avoid ifdefs here, sorry.


-- 
ldv
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