linux-kernel - Re: syscall_get_error() && TS

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Message-ID: <CA+55aFzvb7_LCev0g3bLZH_M+0u0p+=ZK=beizS5edAOK6n_Vw@mail.gmail.com>
Date:   Thu, 30 Mar 2017 12:29:21 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Andy Lutomirski <luto@...capital.net>
Cc:     Oleg Nesterov <oleg@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Andy Lutomirski <luto@...nel.org>,
        Denys Vlasenko <dvlasenk@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>,
        Jan Kratochvil <jan.kratochvil@...hat.com>,
        Pedro Alves <palves@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: syscall_get_error() && TS_ checks

On Thu, Mar 30, 2017 at 12:21 PM, Andy Lutomirski <luto@...capital.net> wrote:
>
> Huh?  Aren't those REX prefixes interpreted as INC instructions or
> similar in compat mode?

Hmm. I think you're right. So it's not like x32 that runs in long mode
but then would use the 64-bit ptrace interface anyway.

Your statement that 64-bit gdb sometimes uses 32-bit compat ptrace
makes me shudder. Why?

Don't even tell me. I suspect I'm happier not knowing.

                   Linus