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From:   Thomas Gleixner <tglx@linutronix.de>
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To:     Joshua Hudson <joshudson@gmail.com>,
        Ammar Faizi <ammarfaizi2@gnuweeb.org>
Cc:     Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        x86-ml <x86@kernel.org>
Subject: Re: System Call trashing registers
In-Reply-To: <CA+jjjYSMq-hKx5XsMDf=+n4wfAr6Btt7x8gpG5kdRRrzr6YK2Q@mail.gmail.com>
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Date:   Fri, 01 Sep 2023 20:49:09 +0200
Message-ID: <87a5u54tlm.ffs@tglx>
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On Fri, Sep 01 2023 at 10:38, Joshua Hudson wrote:
> On Fri, Sep 1, 2023 at 9:24=E2=80=AFAM Ammar Faizi <ammarfaizi2@gnuweeb.o=
rg> wrote:
>
> Correction: it's been fixed again. Sorry about that.

When exactly was it broken? Which kernel version?

The save/restore mechanism is not changing every other day.

> I know the asmutils tools have been broken for a decade, but they're
> working now.
>
> What would happen is system calls that take arguments in ecx and edx woul=
d find
> ecx and edx trashed, but only a few calls actually did this, the
> primary offender
> being open(). The best regression test seems to be hexdump from
> asmutils because the
> corruption would reliably crash the binary. sched_yeild was never an
> affected syscall.

It does absolutely not matter which syscall is used. The save/restore
mechanism is identical for all syscalls.

Thanks,

        tglx