[PATCH] x86-64: Fix TLSDESC relaxation for x32

[Jan Beulich]

On 20.01.2020 16:28, H.J. Lu wrote:
> On Mon, Jan 20, 2020 at 7:18 AM Jan Beulich <jbeulich@suse.com> wrote:
>>
>> On 20.01.2020 15:55, H.J. Lu wrote:
>>> We need to support both sequences for x32.  For both GDesc -> IE/LE
>>> transitions,
>>>
>>> 67 ff 10              call    *x@TLSCALL(%eax)
>>>
>>> should relaxed to
>>>
>>> 0f 1f 00              nopl    (%rax)
>>
>> Since, like it is phrased here, the patch also uses this
>> unconditionally, I wonder if this is the best choice: Linux,
>> for example, has a number of cases where it wouldn't use
>> this NOP form even on 64-bit.
>>
> 
> Assembler has been using this 3-byte NOP in 64-bit for
> a long time.  What other options are you suggesting?

The traditional K8 NOPs (up to three [iirc] 0x66 followed by
0x90), and preferably controllable in some way.

Jan