aarch64: enable rebootstrap, upgrade to gcc11

pkgs/stdenv/cross/default.nix

@@ -1,7 +1,10 @@
 { lib
 , localSystem, crossSystem, config, overlays, crossOverlays ? []
+, rebootstrap ? false
 }:
 
+assert rebootstrap -> throw "bootstrapping is irrelevant to stdenv/cross";
+
 let
   bootStages = import ../. {
     inherit lib localSystem overlays;

pkgs/stdenv/custom/default.nix

@@ -1,7 +1,10 @@
 { lib
 , localSystem, crossSystem, config, overlays, crossOverlays ? []
+, rebootstrap ? false
 }:
 
+assert rebootstrap -> throw "bootstrapping is not relevant to stdenv/custom";
+
 assert crossSystem == localSystem;
 
 let

pkgs/stdenv/darwin/default.nix

@@ -34,9 +34,11 @@
       cpio = fetch { file = "cpio"; sha256 = "sha256-SWkwvLaFyV44kLKL2nx720SvcL4ej/p2V/bX3uqAGO0="; };
       tarball = fetch { file = "bootstrap-tools.cpio.bz2"; sha256 = "sha256-kRC/bhCmlD4L7KAvJQgcukk7AinkMz4IwmG1rqlh5tA="; executable = false; };
     }
+, rebootstrap ? false
 }:
 
 assert crossSystem == localSystem;
+assert rebootstrap -> throw "darwin does not yet support automatic rebootstrapping";
 
 let
   inherit (localSystem) system;

pkgs/stdenv/default.nix

@@ -8,6 +8,13 @@
   lib
   # Args to pass on to the pkgset builder, too
 , localSystem, crossSystem, config, overlays, crossOverlays ? []
+
+# If true, the bootstrapFiles will be rebuilt, resulting in a stdenv
+# built by the same compiler as its bootstrap tools.  Turning this
+# feature on will considerably increase the rebuild cycle, but may
+# help with troubleshooting the bootstrap.
+, rebootstrap ? false
+
 } @ args:
 
 let

pkgs/stdenv/freebsd/default.nix

@@ -1,7 +1,10 @@
 { lib
 , localSystem, crossSystem, config, overlays, crossOverlays ? []
+, rebootstrap ? false
 }:
 
+assert rebootstrap -> throw "stdenv/freebsd does not yet support automatic rebootstrapping";
+
 assert crossSystem == localSystem;
 let inherit (localSystem) system;
     fetchURL = import <nix/fetchurl.nix>;

pkgs/stdenv/linux/default.nix

@@ -59,6 +59,14 @@
 { lib
 , localSystem, crossSystem, config, overlays, crossOverlays ? []
 
+# ARMv8.0 backward compatibility (`-moutline-intrinsics`) currently
+# requires regenerating bootstrapFiles; see:
+#
+#   https://github.com/NixOS/nixpkgs/issues/108111
+#   https://github.com/NixOS/nixpkgs/pull/108200
+#   https://bugzilla.redhat.com/show_bug.cgi?id=1830472
+, rebootstrap ? localSystem.isAarch64
+
 , bootstrapFiles ?
   let table = {
     glibc = {
@@ -93,7 +101,7 @@
   files = archLookupTable.${localSystem.system} or (if getCompatibleTools != null then getCompatibleTools
     else (abort "unsupported platform for the pure Linux stdenv"));
   in files
-}:
+} @args:
 
 assert crossSystem == localSystem;
 
@@ -117,7 +125,7 @@ let
 
 
   # Download and unpack the bootstrap tools (coreutils, GCC, Glibc, ...).
-  bootstrapTools = import (if localSystem.libc == "musl" then ./bootstrap-tools-musl else ./bootstrap-tools) {
+  unpackBootstrapTools = bootstrapFiles: import (if localSystem.libc == "musl" then ./bootstrap-tools-musl else ./bootstrap-tools) {
     inherit system bootstrapFiles;
     extraAttrs = lib.optionalAttrs
       config.contentAddressedByDefault
@@ -135,10 +143,9 @@ let
   # the bootstrap.  In all stages, we build an stdenv and the package
   # set that can be built with that stdenv.
   stageFun = prevStage:
-    { name, overrides ? (self: super: {}), extraNativeBuildInputs ? [] }:
+    { name, overrides ? (self: super: {}), extraNativeBuildInputs ? [], bootstrapTools ? prevStage.bootstrapTools }:
 
     let
-
       thisStdenv = import ../generic {
         name = "${name}-stdenv-linux";
         buildPlatform = localSystem;
@@ -177,33 +184,49 @@ let
           stdenvNoCC = prevStage.ccWrapperStdenv;
         };
 
-        overrides = self: super: (overrides self super) // { fetchurl = thisStdenv.fetchurlBoot; };
+        overrides = self: super: (overrides self super) // {
+          fetchurl = thisStdenv.fetchurlBoot;
+          inherit bootstrapTools;
+        };
       };
-
     in {
       inherit config overlays;
       stdenv = thisStdenv;
     };
 
 in
 
-[
+# when rebootstrapping, we first prepend a copy of the stdenv stages
+# that use the fetched bootstrapFiles:
+lib.optionals rebootstrap (import ./. (args // { rebootstrap = false; })) ++
 
-  ({}: {
+[
+  (prevStage: {
     __raw = true;
-
     gcc-unwrapped = null;
     binutils = null;
     coreutils = null;
     gnugrep = null;
+    bootstrapTools =
+      unpackBootstrapTools
+        (if   rebootstrap
+         then (prevStage.freshBootstrapTools.override {
+           # Copy busybox from the original bootstrapFiles; it is
+           # safe to do this because it is statically linked.  This
+           # avoids having to rebuild a musl-gcc compiler (glibc
+           # doesn't know how to do static linking).
+           busyboxMinimal = prevStage.stdenv.bootstrapFiles.busybox;
+           # don't rebuild a custom compiler
+           bootGCC = prevStage.gcc.cc;
+         }).bootstrapFiles else bootstrapFiles);
   })
 
   # Build a dummy stdenv with no GCC or working fetchurl.  This is
   # because we need a stdenv to build the GCC wrapper and fetchurl.
   #
   # resulting stage0 stdenv:
   # - coreutils, binutils, glibc, gcc: from bootstrapFiles
-  (prevStage: stageFun prevStage {
+  ({ bootstrapTools, ...}@prevStage: stageFun prevStage {
     name = "bootstrap-stage0";
 
     overrides = self: super: {
@@ -477,7 +500,7 @@ in
   #        and the bootstrapTools-built, statically-linked
   #        lib{mpfr,mpc,gmp,isl}.a which are linked into the final gcc
   #        (see commit cfde88976ba4cddd01b1bb28b40afd12ea93a11d).
-  (prevStage: {
+  ({ bootstrapTools, ...}@prevStage: {
     inherit config overlays;
     stdenv = import ../generic rec {
       name = "stdenv-linux";
@@ -504,7 +527,7 @@ in
       inherit (prevStage.stdenv) fetchurlBoot;
 
       extraAttrs = {
-        inherit bootstrapTools;
+        inherit bootstrapTools bootstrapFiles;
         shellPackage = prevStage.bash;
       };
 

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

@@ -1,4 +1,20 @@
-{ pkgs ? import ../../.. {} }:
+{ pkgs ? import ../../.. {}
+, busyboxMinimal ? "${pkgs.busybox.override {
+    useMusl = !pkgs.stdenv.targetPlatform.isRiscV;
+    enableStatic = true;
+    enableMinimal = true;
+    extraConfig = ''
+      CONFIG_ASH y
+      CONFIG_ASH_ECHO y
+      CONFIG_ASH_TEST y
+      CONFIG_ASH_OPTIMIZE_FOR_SIZE y
+      CONFIG_MKDIR y
+      CONFIG_TAR y
+      CONFIG_UNXZ y
+    '';
+  }}/bin/busybox"
+, bootGCC ? pkgs.gcc.cc.override { enableLTO = false; }
+}:
 
 let
   libc = pkgs.stdenv.cc.libc;
@@ -15,22 +31,6 @@ in with pkgs; rec {
 
   tarMinimal = gnutar.override { acl = null; };
 
-  busyboxMinimal = busybox.override {
-    useMusl = !stdenv.targetPlatform.isRiscV;
-    enableStatic = true;
-    enableMinimal = true;
-    extraConfig = ''
-      CONFIG_ASH y
-      CONFIG_ASH_ECHO y
-      CONFIG_ASH_TEST y
-      CONFIG_ASH_OPTIMIZE_FOR_SIZE y
-      CONFIG_MKDIR y
-      CONFIG_TAR y
-      CONFIG_UNXZ y
-    '';
-  };
-
-  bootGCC = gcc.cc.override { enableLTO = false; };
   bootBinutils = binutils.bintools.override {
     withAllTargets = false;
     # Don't need two linkers, disable whatever's not primary/default.
@@ -196,7 +196,7 @@ in with pkgs; rec {
 
         mkdir $out/on-server
         XZ_OPT="-9 -e" tar cvJf $out/on-server/bootstrap-tools.tar.xz --hard-dereference --sort=name --numeric-owner --owner=0 --group=0 --mtime=@1 -C $out/pack .
-        cp ${busyboxMinimal}/bin/busybox $out/on-server
+        cp ${busyboxMinimal} $out/on-server/busybox
         chmod u+w $out/on-server/busybox
         nuke-refs $out/on-server/busybox
       ''; # */

pkgs/stdenv/native/default.nix

@@ -1,8 +1,10 @@
 { lib
 , localSystem, crossSystem, config, overlays, crossOverlays ? []
+, rebootstrap
 }:
 
 assert crossSystem == localSystem;
+assert rebootstrap -> throw "stdenv/native does not yet support automatic rebootstrapping";
 
 let
   inherit (localSystem) system;

pkgs/top-level/all-packages.nix

@@ -14052,7 +14052,6 @@ with pkgs;
   inherit (let
       num =
         if (with stdenv.targetPlatform; isVc4 || libc == "relibc") then 6
-        else if (stdenv.targetPlatform.isAarch64 && stdenv.isLinux) then 9
         else 11;
       numS = toString num;
     in {