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Re: [committed, PATCH] Remove Disp16|Disp32 from 64-bit direct branches
- From: "Jan Beulich" <JBeulich at suse dot com>
- To: "H.J. Lu" <hjl dot tools at gmail dot com>
- Cc: "Binutils" <binutils at sourceware dot org>
- Date: Tue, 12 May 2015 13:20:52 +0100
- 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>
>>> On 12.05.15 at 13:54, <firstname.lastname@example.org> wrote:
> On Tue, May 12, 2015 at 3:41 AM, Jan Beulich <JBeulich@suse.com> wrote:
>>>>> On 11.05.15 at 23:23, <email@example.com> wrote:
>>> Disp16 and Disp32 aren't supported by direct branches in 64-bit mode.
>>> This patch removes them from 64-bit direct branches.
>> See the recent discussion regarding callw - these can certainly have
>> 16-bit displacements on AMD CPUs. And while disassembly may just
>> get "disturbed" by getting this wrong, assembly will produce bad
>> code if you don't account for both cases (or refuse to assemble
>> such mnemonics if they would require size overrides to be added).
>> Apart from that I wonder why you do this for CALL and JMP, but not
>> for Jcc, JCXZ, JRCXZ, LOOP, and LOOPcc.
>> But first of all - please don't bias x86 binutils towards only supporting
>> Intel hardware.
> Can you generate call/jmp with 16-bit displacement in 64-bit mode?
Didn't check whether there is a mechanism currently; of course I
would expect "data16 jmp <label>" to do precisely that.