From 270ee17d414469783daccba718a20e31407c6729 Mon Sep 17 00:00:00 2001
From: Michael Roitzsch <reactorcontrol@icloud.com>
Date: Mon, 15 Feb 2021 20:15:48 +0100
Subject: [PATCH] linux: improve cross compilation with clang

set HOST* variables for host build tools
* do not assume the host compiler is gcc
* pass all build tools to make
---
 pkgs/os-specific/linux/kernel/generate-config.pl |  2 +-
 pkgs/os-specific/linux/kernel/generic.nix        | 10 +++++++---
 2 files changed, 8 insertions(+), 4 deletions(-)

diff --git a/pkgs/os-specific/linux/kernel/generate-config.pl b/pkgs/os-specific/linux/kernel/generate-config.pl
index 6a2aec809a1b..82e1cb66e2be 100644
--- a/pkgs/os-specific/linux/kernel/generate-config.pl
+++ b/pkgs/os-specific/linux/kernel/generate-config.pl
@@ -40,7 +40,7 @@ close ANSWERS;
 sub runConfig {
 
     # Run `make config'.
-    my $pid = open2(\*IN, \*OUT, "make -C $ENV{SRC} O=$buildRoot config SHELL=bash ARCH=$ENV{ARCH}");
+    my $pid = open2(\*IN, \*OUT, "make -C $ENV{SRC} O=$buildRoot config SHELL=bash ARCH=$ENV{ARCH} CC=$ENV{CC} HOSTCC=$ENV{HOSTCC} HOSTCXX=$ENV{HOSTCXX}");
 
     # Parse the output, look for questions and then send an
     # appropriate answer.
diff --git a/pkgs/os-specific/linux/kernel/generic.nix b/pkgs/os-specific/linux/kernel/generic.nix
index ac9d6fbb2b59..e2171a96ab0e 100644
--- a/pkgs/os-specific/linux/kernel/generic.nix
+++ b/pkgs/os-specific/linux/kernel/generic.nix
@@ -131,12 +131,16 @@ let
 
     buildPhase = ''
       export buildRoot="''${buildRoot:-build}"
+      export HOSTCC=$CC_FOR_BUILD
+      export HOSTCXX=$CXX_FOR_BUILD
+      export HOSTAR=$AR_FOR_BUILD
+      export HOSTLD=$LD_FOR_BUILD
 
       # Get a basic config file for later refinement with $generateConfig.
-      make -C .  O="$buildRoot" $kernelBaseConfig \
+      make -C . O="$buildRoot" $kernelBaseConfig \
           ARCH=$kernelArch \
-          HOSTCC=${buildPackages.stdenv.cc.targetPrefix}gcc \
-          HOSTCXX=${buildPackages.stdenv.cc.targetPrefix}g++
+          HOSTCC=$HOSTCC HOSTCXX=$HOSTCXX HOSTAR=$HOSTAR HOSTLD=$HOSTLD \
+          CC=$CC OBJCOPY=$OBJCOPY OBJDUMP=$OBJDUMP READELF=$READELF
 
       # Create the config file.
       echo "generating kernel configuration..."