Re: [PATCHES] gnu: linux-libre: Full retpoline support on x86 [spectre mitigation]

[Alex Vong <alexvong1995@gmail.com>]

Hello Mark,

Mark H Weaver <mhw@netris.org> writes:

> Here are two patches that:
>
> * Add gcc-7.3.0-RC-20180117, which includes support for retpoline.
> * Use gcc-7.3 to build linux-libre on x86 systems.
>
> I'm currently running linux-libre-4.14.14 with full retpoline support:
>
>   mhw@jojen ~$ cd /sys/devices/system/cpu/vulnerabilities
>   mhw@jojen /sys/devices/system/cpu/vulnerabilities$ grep . *
>   meltdown:Mitigation: PTI
>   spectre_v1:Vulnerable
>   spectre_v2:Mitigation: Full generic retpoline
>
> There's also support for retpoline in linux-libre-4.9.77, but none yet
> in earlier kernels.
>
> My question is: should we push these patches to 'master' now, or should
> we wait until gcc-7.3 is released (possibly as soon as January 24)?
>
>       Mark
>
>
[...]

I have a question.

Do we plan to eventually build all programs with all retpoline flags
(-mindirect-branch=thunk, -mfunction-return=thunk, -mindirect-branch-register)
enabled?

In particular, do we build gcc itself with these flags? If so, we will
have to add these flags to BOOT_CFLAGS (which I have problem
understanding how to do it).