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

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Message-ID: <CALCETrUDmn_FoQXnQopO4H2c+N4P=Tv60w2T6G92c4L5_=soQA@mail.gmail.com>
Date:	Thu, 17 Dec 2015 12:27:16 -0800
From:	Andy Lutomirski <luto@...capital.net>
To:	"Dmitry V. Levin" <ldv@...linux.org>
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 Sat, Dec 12, 2015 at 7:44 PM, Dmitry V. Levin <ldv@...linux.org> wrote:
> 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;
> }

Looks good to me.  Want to send a patch?

--Andy
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