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

[Alex Vong <alexvong1995@gmail.com>]

Alex Vong <alexvong1995@gmail.com> writes:

> 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).

I figure it out. We can use 'substitute-keyword-arguments' to alter
'#:make-flags'.