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From:   "H.J. Lu" <hjl.tools@gmail.com>
Date:   Fri, 28 Aug 2020 04:37:28 -0700
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Subject: Re: [PATCH v11 25/25] x86/cet/shstk: Add arch_prctl functions for
 shadow stack
To:     Florian Weimer <fweimer@redhat.com>
Cc:     Andy Lutomirski <luto@kernel.org>,
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        Dave Martin <Dave.Martin@arm.com>,
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On Thu, Aug 27, 2020 at 11:24 PM Florian Weimer <fweimer@redhat.com> wrote:
>
> * H. J. Lu:
>
> > Can you think of ANY issues of passing more arguments to arch_prctl?
>
> On x32, the glibc arch_prctl system call wrapper only passes two
> arguments to the kernel, and applications have no way of detecting that.
> musl only passes two arguments on all architectures.  It happens to work
> anyway with default compiler flags, but that's an accident.

In the current glibc, there is no arch_prctl wrapper for i386.  There are
arch_prctl wrappers with 2 arguments for x86-64 and x32.  But this isn't an
issue for glibc since glibc is both the provider and the user of the new
arch_prctl extension.  Besides,

long syscall(long number, ...);

is always available.

-- 
H.J.