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From:   "H.J. Lu" <hjl.tools@gmail.com>
Date:   Thu, 27 Aug 2020 06:28:56 -0700
Message-ID: <CAMe9rOrhjLSaMNABnzd=Kp5UeVot1Qkx0_PnMng=sT+wd9Xubw@mail.gmail.com>
Subject: Re: [PATCH v11 25/25] x86/cet/shstk: Add arch_prctl functions for
 shadow stack
To:     Florian Weimer <fweimer@redhat.com>
Cc:     Dave Martin <Dave.Martin@arm.com>,
        "Yu, Yu-cheng" <yu-cheng.yu@intel.com>,
        Dave Hansen <dave.hansen@intel.com>,
        Andy Lutomirski <luto@kernel.org>, X86 ML <x86@kernel.org>,
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        Balbir Singh <bsingharora@gmail.com>,
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        Cyrill Gorcunov <gorcunov@gmail.com>,
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On Thu, Aug 27, 2020 at 6:19 AM Florian Weimer <fweimer@redhat.com> wrote:
>
> * Dave Martin:
>
> > You're right that this has implications: for i386, libc probably pulls
> > more arguments off the stack than are really there in some situations.
> > This isn't a new problem though.  There are already generic prctls with
> > fewer than 4 args that are used on x86.
>
> As originally posted, glibc prctl would have to know that it has to pull
> an u64 argument off the argument list for ARCH_X86_CET_DISABLE.  But
> then the u64 argument is a problem for arch_prctl as well.
>

Argument of ARCH_X86_CET_DISABLE is int and passed in register.

-- 
H.J.