linux-kernel - Re: [PATCH] x86/asm/64: do not clear high 32 bits of syscall number when CONFIG_X86

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Date:   Fri, 15 Sep 2017 18:12:43 +0200
From:   Oleg Nesterov <oleg@...hat.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        Andy Lutomirski <luto@...nel.org>,
        Eugene Syromyatnikov <evgsyr@...il.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86/asm/64: do not clear high 32 bits of syscall number
 when CONFIG_X86_X32=y

On 09/14, Dmitry V. Levin wrote:
>
> On Wed, Sep 13, 2017 at 06:49:21PM +0200, Oleg Nesterov wrote:
>
> > do_syscall_64() does "nr & __SYSCALL_MASK" unconditionally,
>
> yes
>
> > this clears the upper bits, no?
>
> Why?  As "nr" is of type "unsigned long" and __SYSCALL_MASK is either
> (~(__X32_SYSCALL_BIT)) or (~0), that is, an integer with the sign bit set,

Yes, thanks for correcting me, it is "int" but somehow I thought it is
"unsigned int".

Oleg.