lockdep: 4.1.2 -> 5.0.21, fix build, enable tests

required a bit of an overhaul to ensure we're compiling against *this*
kernel's headers, not those in glibc which are presumably from some other
random kernel version.

would be nice to update to a more recent version, the build of this tool
reportedly got broken soon after this release.

pkgs/os-specific/linux/lockdep/default.nix

@@ -1,16 +1,47 @@
-{ stdenv, fetchurl }:
+{ stdenv, fetchurl, bash, flex, bison, valgrind }:
 
 stdenv.mkDerivation rec {
   pname = "lockdep";
-  version = "4.1.2";
-  fullver = "4.1.2";
 
+  # it would be nice to be able to pick a kernel version in sync with something
+  # else we already ship, but it seems userspace lockdep isn't very well maintained
+  # and appears broken in many kernel releases
+  version = "5.0.21";
+  fullver = "5.0.21";
   src = fetchurl {
-    url = "mirror://kernel/linux/kernel/v4.x/linux-${version}.tar.xz";
-    sha256 = "1mdyjhnzhh254cblahqmpsk226z006z6sm9dmwvg6jlhpsw4cjhy";
+    url = "mirror://kernel/linux/kernel/v5.x/linux-${version}.tar.xz";
+    sha256 = "1my2m9hvnvdrvzcg0fgqgaga59y2cd5zlpv7xrfj2nn98sjhglwq";
   };
 
-  preConfigure = "cd tools/lib/lockdep";
+  # ensure *this* kernel's userspace-headers are picked up before we
+  # fall back to those in glibc, as they will be from a mismatched
+  # kernel version
+  postPatch = ''
+    substituteInPlace tools/lib/lockdep/Makefile \
+      --replace 'CONFIG_INCLUDES =' $'CONFIG_INCLUDES = -I../../../usr/include\n#'
+  '';
+
+  nativeBuildInputs = [ flex bison ];
+
+  buildPhase = ''
+    make defconfig
+    make headers_install
+    cd tools/lib/lockdep
+    make
+  '';
+
+  doCheck = true;
+  checkInputs = [ valgrind ];
+  checkPhase = ''
+    # there are more /bin/bash references than just shebangs
+    for f in lockdep run_tests.sh tests/*.sh; do
+      substituteInPlace $f \
+        --replace '/bin/bash' '${bash}/bin/bash'
+    done
+
+    ./run_tests.sh
+  '';
+
   installPhase = ''
     mkdir -p $out/bin $out/lib $out/include