linux-kernel - Re: [PATCH v3 06/10] x86: elf: Use e_machine to select start

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Date:   Wed, 7 Oct 2020 17:05:51 -0700
From:   Andy Lutomirski <luto@...nel.org>
To:     Gabriel Krisman Bertazi <krisman@...labora.com>
Cc:     Andrew Lutomirski <luto@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Christoph Hellwig <hch@....de>,
        "H. Peter Anvin" <hpa@...or.com>, Borislav Petkov <bp@...en8.de>,
        Robert Richter <rric@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>, X86 ML <x86@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "Christopherson, Sean J" <sean.j.christopherson@...el.com>,
        kernel@...labora.com
Subject: Re: [PATCH v3 06/10] x86: elf: Use e_machine to select start_thread
 for x32

On Sat, Oct 3, 2020 at 8:26 PM Gabriel Krisman Bertazi
<krisman@...labora.com> wrote:
>
> Since TIF_X32 is going away, avoid using it to find the ELF type in
> compat_start_thread.
>
> According to SysV AMD64 ABI Draft, an AMD64 ELF object using ILP32 must
> have ELFCLASS32 with (E_MACHINE == EM_X86_64), so use that ELF field to
> differentiate a x32 object from a IA32 object when executing
> start_thread in compat mode.

Hmm, I suppose I can live with this.  It's not fundamentally worse
than any of the other ELF compat hacks.

Reviewed-by: Andy Lutomirski <luto@...nel.org>