Re: [PATCH 1/5] x86: Add -mindirect-branch=

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

On Mon, Jan 8, 2018 at 9:18 AM, Michael Matz <matz@suse.de> wrote:
> Hi,
>
> On Mon, 8 Jan 2018, H.J. Lu wrote:
>
>> On Mon, Jan 8, 2018 at 4:00 AM, Jakub Jelinek <jakub@redhat.com> wrote:
>> > On Mon, Jan 08, 2018 at 03:55:52AM -0800, H.J. Lu wrote:
>> >> > I'm wondering whether thunk creation can be a good target-independent generalization? I guess
>> >> > we can emit the function declaration without direct writes to asm_out_file? And the emission
>> >> > of function body can be potentially a target hook?
>> >> >
>> >> > What about emitting body of the function with RTL instructions instead of direct assembly write?
>> >> > My knowledge of RTL is quite small, but maybe it can bring some generalization and reusability
>> >> > for other targets?
>> >>
>> >> Thunks are x86 specific and they are created the same way as 32-bit PIC thunks.
>> >> I don't see how a target hook is used.
>> >
>> > Talking about PIC thunks, those have I believe . character in their symbols,
>> > so that they can't be confused with user functions.  Any reason these
>> > retpoline thunks aren't?
>> >
>>
>> They used to have '.'.  It was changed at the last minute since kernel
>> needs to export them as regular symbols.
>
> That can be done via asm aliases or direct assembler use; the kernel
> doesn't absolutely have to access them via C compatible symbol names.
>

Hi David,

Can you comment on this?


-- 
H.J.