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Subject: Re: There is *NO* abi stability in -head
From: David Chisnall <theraven@FreeBSD.org>
In-Reply-To: <CAGudoHERrva8esddVU66PhZYL+Zjmh8JtWXFtH4=vBZcTX-aQg@mail.gmail.com>
Date: Tue, 24 Oct 2017 09:18:50 +0100
Cc: FreeBSD Current <freebsd-current@freebsd.org>
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References: <CAGudoHERrva8esddVU66PhZYL+Zjmh8JtWXFtH4=vBZcTX-aQg@mail.gmail.com>
To: Mateusz Guzik <mjguzik@gmail.com>
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On 23 Oct 2017, at 21:35, Mateusz Guzik <mjguzik@gmail.com> wrote:
>=20
> Instead, the same can be reshuffled:
> struct crap2 {
>        int i1;
>        int i2;
>        void *p1;
>        void *p2;
> };
>=20
> With offsets:
>=20
> 0x1000 i1
> 0x1004 i2
> 0x1008 p1
> 0x1010 p2
>=20
> This is only 24 bytes. 2 ints can be placed together and since they =
add
> up to 8 the p1 pointer gets the right alignment without extra padding.

If you are making changes of this nature, please consider sorting in the =
other order.  When we start seeing 128-bit pointers (which, with =
CHERI-like systems, may be sooner than you think) then this ordering =
will give you lots of padding, whereas putting the pointers first will =
not.

David