From 972c7e99ff692a465509604027d65c28adde3aca Mon Sep 17 00:00:00 2001
From: toonn <toonn@toonn.io>
Date: Tue, 15 Feb 2022 19:23:03 +0100
Subject: [PATCH] Libsystem: Replace cpio with copyHierarchy

I noticed every time building Libsystem that there was a very slow phase
where the output consisted of many lines like `42 blocks`. This is
output from cpio and in brief testing it takes at least twice as long to
go through cpio for the simple copies we want to make. The interface is
very convenient but the performance penalty is very painful so I decided
to implement a function that emulates cpio's interface.

On my machine with a 7200 RPM HDD this speeds up the build from about
250 minutes to about 75 seconds, a factor of 200! I'm not certain the
results on modern hardware would be similarly positive so this could use
further testing.
---
 .../Libsystem/default.nix                      | 18 ++++++++++++------
 1 file changed, 12 insertions(+), 6 deletions(-)

diff --git a/pkgs/os-specific/darwin/apple-source-releases/Libsystem/default.nix b/pkgs/os-specific/darwin/apple-source-releases/Libsystem/default.nix
index 86c91e9b55c..6f8124dbac4 100644
--- a/pkgs/os-specific/darwin/apple-source-releases/Libsystem/default.nix
+++ b/pkgs/os-specific/darwin/apple-source-releases/Libsystem/default.nix
@@ -1,5 +1,5 @@
 { lib, stdenv, buildPackages
-, appleDerivation', cpio, xnu, Libc, Libm, libdispatch, Libinfo
+, appleDerivation', xnu, Libc, Libm, libdispatch, Libinfo
 , dyld, Csu, architecture, libclosure, CarbonHeaders, ncurses, CommonCrypto
 , copyfile, removefile, libresolvHeaders, libresolv, Libnotify, libplatform, libpthread
 , mDNSResponder, launchd, libutilHeaders, hfsHeaders, darling, darwin-stubs
@@ -11,15 +11,21 @@ appleDerivation' stdenv {
   dontBuild = true;
   dontFixup = true;
 
-  nativeBuildInputs = [ cpio ];
-
   installPhase = ''
     export NIX_ENFORCE_PURITY=
 
     mkdir -p $out/lib $out/include
 
+    function copyHierarchy () {
+      mkdir -p $1
+      while read f; do
+        mkdir -p $1/$(dirname $f)
+        cp --parents -pn $f $1
+      done
+    }
+
     # Set up our include directories
-    (cd ${xnu}/include && find . -name '*.h' -or -name '*.defs' | cpio -pdm $out/include)
+    (cd ${xnu}/include && find . -name '*.h' -or -name '*.defs' | copyHierarchy $out/include)
     cp ${xnu}/Library/Frameworks/Kernel.framework/Versions/A/Headers/Availability*.h $out/include
     cp ${xnu}/Library/Frameworks/Kernel.framework/Versions/A/Headers/stdarg.h        $out/include
 
@@ -28,10 +34,10 @@ appleDerivation' stdenv {
                ${CommonCrypto} ${copyfile} ${removefile} ${libresolvHeaders} \
                ${Libnotify} ${libplatform} ${mDNSResponder} ${launchd} \
                ${libutilHeaders} ${libpthread} ${hfsHeaders}; do
-      (cd $dep/include && find . -name '*.h' | cpio -pdm $out/include)
+      (cd $dep/include && find . -name '*.h' | copyHierarchy $out/include)
     done
 
-    (cd ${buildPackages.darwin.cctools.dev}/include/mach-o && find . -name '*.h' | cpio -pdm $out/include/mach-o)
+    (cd ${buildPackages.darwin.cctools.dev}/include/mach-o && find . -name '*.h' | copyHierarchy $out/include/mach-o)
 
     mkdir -p $out/include/os