Re: [PATCH 13/22] signal: Move addr_lsb into the _sigfault union for clarity

[Dave Hansen]

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?