stdenv: Bringup aarch64 architecture support

lib/platforms.nix

···
   freebsd = ["i686-freebsd" "x86_64-freebsd"];
   gnu = linux; /* ++ hurd ++ kfreebsd ++ ... */
   illumos = ["x86_64-solaris"];
-  linux = ["i686-linux" "x86_64-linux" "armv5tel-linux" "armv6l-linux" "armv7l-linux" "mips64el-linux"];
+  linux = ["i686-linux" "x86_64-linux" "armv5tel-linux" "armv6l-linux" "armv7l-linux" "aarch64-linux" "mips64el-linux"];
   netbsd = ["i686-netbsd" "x86_64-netbsd"];
   openbsd = ["i686-openbsd" "x86_64-openbsd"];
   unix = linux ++ darwin ++ freebsd ++ openbsd ++ netbsd ++ illumos;

pkgs/build-support/cc-wrapper/default.nix

···
        if stdenv.system == "x86_64-linux" then "ld-linux-x86-64.so.2" else
        # ARM with a wildcard, which can be "" or "-armhf".
        if stdenv.isArm then "ld-linux*.so.3" else
+       if stdenv.system == "aarch64-linux" then "ld-linux-aarch64.so.1" else
        if stdenv.system == "powerpc-linux" then "ld.so.1" else
        if stdenv.system == "mips64el-linux" then "ld.so.1" else
        if stdenv.system == "x86_64-darwin" then "/usr/lib/dyld" else

pkgs/stdenv/default.nix

···
     "armv5tel-linux" = stagesLinux;
     "armv6l-linux" = stagesLinux;
     "armv7l-linux" = stagesLinux;
+    "aarch64-linux" = stagesLinux;
     "mips64el-linux" = stagesLinux;
     "powerpc-linux" = /* stagesLinux */ stagesNative;
     "x86_64-darwin" = stagesDarwin;

pkgs/stdenv/generic/default.nix

···
              || system == "armv5tel-linux"
              || system == "armv6l-linux"
              || system == "armv7l-linux"
+             || system == "aarch64-linux"
              || system == "mips64el-linux";
       isGNU = system == "i686-gnu"; # GNU/Hurd
       isGlibc = isGNU # useful for `stdenvNative'
···
       isArm = system == "armv5tel-linux"
            || system == "armv6l-linux"
            || system == "armv7l-linux";
+      isAarch64 = system == "aarch64-linux";
       isBigEndian = system == "powerpc-linux";
 
       # Whether we should run paxctl to pax-mark binaries.

pkgs/stdenv/linux/default.nix

···
     "armv5tel-linux" = import ./bootstrap-files/armv5tel.nix;
     "armv6l-linux" = import ./bootstrap-files/armv6l.nix;
     "armv7l-linux" = import ./bootstrap-files/armv7l.nix;
+    "aarch64-linux" = import ./bootstrap-files/aarch64.nix;
     "mips64el-linux" = import ./bootstrap-files/loongson2f.nix;
   }.${localSystem.system}
     or (abort "unsupported platform for the pure Linux stdenv")

pkgs/stdenv/linux/make-bootstrap-tools-cross.nix

···
     };
   };
 
+  aarch64-multiplatform-crossSystem = {
+    crossSystem = rec {
+      config = "aarch64-linux-gnu";
+      bigEndian = false;
+      arch = "aarch64";
+      withTLS = true;
+      libc = "glibc";
+      platform = pkgsNoParams.platforms.aarch64-multiplatform;
+      inherit (platform) gcc;
+    };
+  };
+
   selectedCrossSystem =
     if toolsArch == "armv5tel" then sheevaplugCrossSystem else
     if toolsArch == "armv6l" then raspberrypiCrossSystem else
-    if toolsArch == "armv7l" then armv7l-hf-multiplatform-crossSystem else null;
+    if toolsArch == "armv7l" then armv7l-hf-multiplatform-crossSystem else
+    if toolsArch == "aarch64" then aarch64-multiplatform-crossSystem else null;
 
   pkgsUnspliced = pkgsFun ({inherit system;} // selectedCrossSystem);
   pkgs = pkgsUnspliced.splicedPackages;
···
     armv5tel = buildFor "armv5tel";
     armv6l = buildFor "armv6l";
     armv7l = buildFor "armv7l";
+    aarch64 = buildFor "aarch64";
 }

pkgs/top-level/platforms.nix

···
     };
   };
 
+  aarch64-multiplatform = {
+    name = "aarch64-multiplatform";
+    kernelMajor = "2.6"; # Using "2.6" enables 2.6 kernel syscalls in glibc.
+    kernelHeadersBaseConfig = "defconfig";
+    kernelBaseConfig = "defconfig";
+    kernelArch = "arm64";
+    kernelDTB = true;
+    kernelAutoModules = false;
+    kernelExtraConfig = "";
+    uboot = null;
+    kernelTarget = "Image";
+    gcc = {
+      arch = "armv8-a";
+    };
+  };
+
   selectPlatformBySystem = system: {
       "i686-linux" = pc32;
       "x86_64-linux" = pc64;
       "armv5tel-linux" = sheevaplug;
       "armv6l-linux" = raspberrypi;
       "armv7l-linux" = armv7l-hf-multiplatform;
+      "aarch64-linux" = aarch64-multiplatform;
       "mips64el-linux" = fuloong2f_n32;
     }.${system} or pcBase;
 }