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

[Mark H Weaver]

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:

  address@hidden ~$ cd /sys/devices/system/cpu/vulnerabilities
  address@hidden /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


>From 387a02c3f9e157bdf40b2b5ad0e53e5b209f3aa5 Mon Sep 17 00:00:00 2001
From: Mark H Weaver <address@hidden>
Date: Sat, 20 Jan 2018 15:15:19 -0500
Subject: [PATCH 1/2] gnu: gcc: Add gcc 7.3.0-RC-20180117 [includes retpoline
 support].

* gnu/packages/gcc.scm (gcc-7.3): New variable.
---
 gnu/packages/gcc.scm | 20 +++++++++++++++++++-
 1 file changed, 19 insertions(+), 1 deletion(-)

diff --git a/gnu/packages/gcc.scm b/gnu/packages/gcc.scm
index ad8992289..288c4deb3 100644
--- a/gnu/packages/gcc.scm
+++ b/gnu/packages/gcc.scm
@@ -1,6 +1,6 @@
 ;;; GNU Guix --- Functional package management for GNU
 ;;; Copyright © 2012, 2013, 2014, 2015, 2016, 2017 Ludovic Courtès 
<address@hidden>
-;;; Copyright © 2014, 2015 Mark H Weaver <address@hidden>
+;;; Copyright © 2014, 2015, 2018 Mark H Weaver <address@hidden>
 ;;; Copyright © 2014, 2015, 2016, 2017 Ricardo Wurmus <address@hidden>
 ;;; Copyright © 2015 Andreas Enge <address@hidden>
 ;;; Copyright © 2015, 2016, 2017 Efraim Flashner <address@hidden>
@@ -433,6 +433,24 @@ Go.  It also includes runtime support libraries for these 
languages.")
 for several languages, including C, C++, Objective-C, Fortran, Ada, and Go.
 It also includes runtime support libraries for these languages.")))
 
+(define-public gcc-7.3
+  (package
+    (inherit gcc-7)
+    (version "7.3.0-RC-20180117")
+    (source (origin
+              (method url-fetch)
+              (uri (string-append "ftp://gcc.gnu.org/pub/gcc/snapshots/";
+                                  version "/gcc-" version ".tar.xz"))
+              (sha256
+               (base32
+                "0g447y7q1mdflzkw38d2ycb5w73bgzr5zbwn6135q314wrx6fxp2"))
+              (patches (search-patches "gcc-strmov-store-file-names.patch"
+                                       "gcc-5.0-libvtv-runpath.patch"))))
+    (description
+     "GCC is the GNU Compiler Collection.  It provides compiler front-ends
+for several languages, including C, C++, Objective-C, Fortran, Ada, and Go.
+It also includes runtime support libraries for these languages.")))
+
 ;; Note: When changing the default gcc version, update
 ;;       the gcc-toolchain-* definitions and the gfortran definition
 ;;       accordingly.
-- 
2.15.1

>From d78c7ffa76c3cd2252bd0753c73e88468755184d Mon Sep 17 00:00:00 2001
From: Mark H Weaver <address@hidden>
Date: Sat, 20 Jan 2018 15:16:20 -0500
Subject: [PATCH 2/2] gnu: linux-libre: Full retpoline support on x86
 [mitigates spectre].

* gnu/packages/linux.scm (make-linux-libre): On x86 systems, build with
gcc-7.3.
---
 gnu/packages/linux.scm | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/gnu/packages/linux.scm b/gnu/packages/linux.scm
index 13e08f265..2425fc709 100644
--- a/gnu/packages/linux.scm
+++ b/gnu/packages/linux.scm
@@ -283,6 +283,12 @@ for ARCH and optionally VARIANT, or #f if there is no such 
configuration."
        ("bc" ,bc)
        ("openssl" ,openssl)
        ("kmod" ,kmod)
+       ,@(match (system->linux-architecture
+                 (or (%current-target-system) (%current-system)))
+           ((or "x86_64" "i386")
+            `(("gcc" ,gcc-7.3)))
+           (_
+            '()))
        ,@(match (and configuration-file
                      (configuration-file
                       (system->linux-architecture
-- 
2.15.1