From a12606bef42e79184c18e89146df6319e4715884 Mon Sep 17 00:00:00 2001
From: Bernardo Meurer <bernardo@meurer.org>
Date: Thu, 2 Sep 2021 01:20:49 -0700
Subject: [PATCH] linuxPackages.zfs: use the kernel's stdenv when possible

---
 pkgs/os-specific/linux/zfs/default.nix | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/pkgs/os-specific/linux/zfs/default.nix b/pkgs/os-specific/linux/zfs/default.nix
index 78cced512a48..a9f1f1c389b3 100644
--- a/pkgs/os-specific/linux/zfs/default.nix
+++ b/pkgs/os-specific/linux/zfs/default.nix
@@ -26,6 +26,14 @@ let
   buildKernel = any (n: n == configFile) [ "kernel" "all" ];
   buildUser = any (n: n == configFile) [ "user" "all" ];
 
+  # XXX: You always want to build kernel modules with the same stdenv as the
+  # kernel was built with. However, since zfs can also be built for userspace we
+  # need to correctly pick between the provided/default stdenv, and the one used
+  # by the kernel.
+  # If you don't do this your ZFS builds will fail on any non-standard (e.g.
+  # clang-built) kernels.
+  stdenv' = if kernel == null then stdenv else kernel.stdenv;
+
   common = { version
     , sha256
     , extraPatches ? []
@@ -34,7 +42,7 @@ let
     , latestCompatibleLinuxPackages
     , kernelCompatible ? null }:
 
-    stdenv.mkDerivation {
+    stdenv'.mkDerivation {
       name = "zfs-${configFile}-${version}${optionalString buildKernel "-${kernel.version}"}";
 
       src = fetchFromGitHub {