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Re: [PATCH 0/5] x86: CVE-2017-5715, aka Spectre
> On Tue, Jan 16, 2018 at 9:34 AM, Jan Hubicka <hubicka@ucw.cz> wrote:
> >> On Mon, Jan 15, 2018 at 5:53 PM, H.J. Lu <hjl.tools@gmail.com> wrote:
> >> > On Mon, Jan 15, 2018 at 3:38 AM, H.J. Lu <hjl.tools@gmail.com> wrote:
> >> >> On Mon, Jan 15, 2018 at 12:31 AM, Richard Biener
> >> >> <richard.guenther@gmail.com> wrote:
> >> >>> On Sun, Jan 14, 2018 at 4:08 PM, H.J. Lu <hjl.tools@gmail.com> wrote:
> >> >>>> Now my patch set has been checked into trunk. Here is a patch set
> >> >>>> to move struct ix86_frame to machine_function on GCC 7, which is
> >> >>>> needed to backport the patch set to GCC 7:
> >> >>>>
> >> >>>> https://gcc.gnu.org/ml/gcc-patches/2018-01/msg01239.html
> >> >>>> https://gcc.gnu.org/ml/gcc-patches/2018-01/msg01240.html
> >> >>>> https://gcc.gnu.org/ml/gcc-patches/2018-01/msg01241.html
> >> >>>>
> >> >>>> OK for gcc-7-branch?
> >> >>>
> >> >>> Yes, backporting is ok - please watch for possible fallout on trunk and make
> >> >>> sure to adjust the backport accordingly. I plan to do GCC 7.3 RC1 on
> >> >>> Wednesday now with the final release about a week later if no issue shows
> >> >>> up.
> >> >>>
> >> >>
> >> >> Backport is blocked by
> >> >>
> >> >> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83838
> >> >>
> >> >> There are many test failures due to lack of comdat support in linker on Solaris.
> >> >> I can limit these tests to Linux.
> >> >
> >> > These are testcase issues and shouldn't block backport to GCC 7.
> >>
> >> It makes the option using thunks unusable though, right? Can you simply make
> >> them hidden on systems without comdat support? That duplicates them per TU
> >> but at least the feature works. Or those systems should provide the thunks via
> >> libgcc.
> >>
> >> I agree we can followup with a fix for Solaris given lack of a public
> >> testing machine.
> >
> > My memory is bit dim, but I am convinced I was fixing specific errors for comdats
> > on Solaris, so I think the toolchain supports them in some sort, just is more
> > restrictive/different from GNU implementation.
> >
> > Indeed, i think just producing sorry, unimplemented message is what we should do
> > if we can't support retpoline on given target.
>
> I'm quite sure Solaris supports comdats, after all it invented ELF ;)
> I've also seen
> comdats in debugging early LTO issues. We might run into Solaris as
> issues though.
:)
My recollection is that the thunks in a comdat group needs to come in specific
order after the entry symbol. Probably after - at some point I tried to move the
before (for better code layout) and needed to retreat.
Honza