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

[Leo Famulari <leo@famulari.name>]

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On Sat, Jan 20, 2018 at 03:34:08PM -0500, Mark H Weaver wrote:
> 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)?

I'm used this compiler and Guix packages to build a custom Linux 4.14.14
and have used it on my laptop for a day or so now. No problems and the
kernel does see the retpoline:

$ grep . /sys/devices/system/cpu/vulnerabilities/*
/sys/devices/system/cpu/vulnerabilities/meltdown:Mitigation: PTI
/sys/devices/system/cpu/vulnerabilities/spectre_v1:Vulnerable
/sys/devices/system/cpu/vulnerabilities/spectre_v2:Mitigation: Full generic retpoline

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