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Re: [committed, PATCH] Remove Disp16|Disp32 from 64-bit direct branches
- From: Michael Matz <matz at suse dot de>
- To: "H.J. Lu" <hjl dot tools at gmail dot com>
- Cc: Jan Beulich <JBeulich at suse dot com>, Binutils <binutils at sourceware dot org>
- Date: Tue, 12 May 2015 17:32:30 +0200 (CEST)
- Subject: Re: [committed, PATCH] Remove Disp16|Disp32 from 64-bit direct branches
- Authentication-results: sourceware.org; auth=none
- References: <20150511212331 dot GA1838 at intel dot com> <5551F4E70200007800079575 at mail dot emea dot novell dot com> <CAMe9rOpDbkeFbmNbQh0a1AKhAQy-cH4HJu20o_ERQaoR6sTxbQ at mail dot gmail dot com> <55520C440200007800079718 at mail dot emea dot novell dot com> <CAMe9rOpFgSyJm-oceuDkrBYnBQGv01ywCc43WySqX21NTJYi4Q at mail dot gmail dot com> <555216370200007800079773 at mail dot emea dot novell dot com> <CAMe9rOpOx=SSUZnCFimn4fBzFqNRDch8QYLn3Os_y7EfQH65Qw at mail dot gmail dot com> <alpine dot LSU dot 2 dot 20 dot 1505121548100 dot 4883 at wotan dot suse dot de> <CAMe9rOqg_H9YXHdoWv-k4zoQm77OoQ19j3djHZ74pgUORiDECw at mail dot gmail dot com> <alpine dot LSU dot 2 dot 20 dot 1505121559480 dot 4883 at wotan dot suse dot de> <CAMe9rOpmOBJoRNy8QGQn03eQJrzsUk+MTzJJuQu_DD1kxXV5pg at mail dot gmail dot com> <alpine dot LSU dot 2 dot 20 dot 1505121713290 dot 4883 at wotan dot suse dot de> <CAMe9rOrwY-MmZcPPxEo7NsO1O6yR4K6rO08j-SvmivOYXGuNag at mail dot gmail dot com>
Hi,
On Tue, 12 May 2015, H.J. Lu wrote:
> >> I thought it did jump to "(nextip + offset) & 0xffff" on AMD. Can
> >> you verify if it is true?
> >
> > Sorry, yes, this is true, the 16bit operand size prefix truncates RIP
> > to 16 bit. Nevertheless it's a valid instruction and works as
> > documented.
>
> It doesn't work on Intel processors. Can you show me a real usage for
> this?
Why should I? Obviously in linux there are no uses, but perhaps in BIOS
or boot loader code, or micro-OSes and the like. Can you instead show me
why you want to remove support for it?
Ciao,
Michael.
- References:
- [committed, PATCH] Remove Disp16|Disp32 from 64-bit direct branches
- Re: [committed, PATCH] Remove Disp16|Disp32 from 64-bit direct branches
- Re: [committed, PATCH] Remove Disp16|Disp32 from 64-bit direct branches
- Re: [committed, PATCH] Remove Disp16|Disp32 from 64-bit direct branches
- Re: [committed, PATCH] Remove Disp16|Disp32 from 64-bit direct branches
- Re: [committed, PATCH] Remove Disp16|Disp32 from 64-bit direct branches
- Re: [committed, PATCH] Remove Disp16|Disp32 from 64-bit direct branches
- Re: [committed, PATCH] Remove Disp16|Disp32 from 64-bit direct branches
- Re: [committed, PATCH] Remove Disp16|Disp32 from 64-bit direct branches
- Re: [committed, PATCH] Remove Disp16|Disp32 from 64-bit direct branches
- Re: [committed, PATCH] Remove Disp16|Disp32 from 64-bit direct branches
- Re: [committed, PATCH] Remove Disp16|Disp32 from 64-bit direct branches
- Re: [committed, PATCH] Remove Disp16|Disp32 from 64-bit direct branches