Re: PING: [PATCH] i386: Add TARGET_INDIRECT_BRANCH_REGISTER

["H.J. Lu" <hjl.tools@gmail.com>]

On Thu, Feb 22, 2018 at 9:10 AM, Jeff Law <law@redhat.com> wrote:
> On 02/22/2018 07:38 AM, Jan Hubicka wrote:
>>>>>
>>>>> Hi Jan,
>>>>>
>>>>> https://gcc.gnu.org/ml/gcc-patches/2018-01/msg02233.html
>>>>>
>>>>> Is OK for trunk?
>>>>
>>>> I see that using register makes the problem go away and pushing address to stack
>>>> seemed bit odd anyway. However how does this work on other types of thunk?
>>>
>>> Kernel only uses  -mindirect-branch=thunk-extern.  I am working on a proposal
>>> to use -mindirect-branch=thunk-extern in user space to support CET in a single
>>> binary.  So at the end of the day, only
>>> -mindirect-branch=thunk-extern will be used.
>>
>> OK, so it is about the fact that we do not really want to support all
>> -mindirect-branch options in the future? If we don't want to support the correctly,
>> I wonder why we are including them at all.  Shall we at least output warning/sorry
>> when user tries other thunk type with stack unwinding enabled?
>> (does Kernel use it?)
> A few notes.
>
> 1. It's not even clear at this time that retpolining user space binaries
> makes any sense at all.   SO before doing anything to make this easier
> I'd like to see a justification for why it's really needed.

Hi Jeff,

Which part were commenting? My patch to add TARGET_INDIRECT_BRANCH_REGISTER
or removing -mindirect-branch choices?

> 2. On the other hand, the existing thunk options do make it easier to
> test independent of hte kernel.  ie, I can turn on inline thunks by
> default and test things in user space (ie, do thunks generally work
> properly).

It sounds reasonable.


-- 
H.J.