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Subject: Re: [PATCH 13/22] signal: Move addr_lsb into the _sigfault union for
 clarity
To:     "Eric W. Biederman" <ebiederm@xmission.com>,
        linux-kernel@vger.kernel.org
References: <87k1wimybi.fsf_-_@xmission.com>
 <20180116004009.31036-13-ebiederm@xmission.com>
Cc:     Al Viro <viro@zeniv.linux.org.uk>, Oleg Nesterov <oleg@redhat.com>,
        linux-arch@vger.kernel.org
From:   Dave Hansen <dave.hansen@intel.com>
Message-ID: <29eb3438-0891-36ee-e5f6-36e26ccf2b89@intel.com>
Date:   Fri, 16 Mar 2018 12:00:16 -0700
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On 01/15/2018 04:40 PM, Eric W. Biederman wrote:
> The addr_lsb fields is only valid and available when the
> signal is SIGBUS and the si_code is BUS_MCEERR_AR or BUS_MCEERR_AO.
> Document this with a comment and place the field in the _sigfault union
> to make this clear.
> 
> All of the fields stay in the same physical location so both the old
> and new definitions of struct siginfo will continue to work.

This breaks the ABI and breaks protection keys.  The physical locations
*DO* change.

Before this patch:

#define si_pkey         _sifields._sigfault._pkey
(gdb) print &((siginfo_t *)0)->_sifields._sigfault._pkey
$1 = (__u32 *) 0x20 <irq_stack_union+32>

and after:

+#define si_pkey                _sifields._sigfault._addr_pkey._pkey
(gdb) print &((siginfo_t *)0)->_sifields._sigfault._addr_pkey._pkey
$1 = (__u32 *) 0x1c

Can we revert this, please?