llvmPackages.bolt: add experimental bolt hook

lib/systems/default.nix

@@ -93,6 +93,8 @@ let
       # Derived meta-data
       useLLVM = final.isFreeBSD || final.isOpenBSD;
 
+      useBolt = false;
+
       libc =
         /**/ if final.isDarwin                then "libSystem"
         else if final.isMinGW                 then "msvcrt"

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

@@ -728,6 +728,14 @@ stdenvNoCC.mkDerivation {
       substituteAll ${./add-clang-cc-cflags-before.sh} $out/nix-support/add-local-cc-cflags-before.sh
     ''
 
+    ###
+    ### Bolt support
+    ### Binaries need to be linked with relocations.
+    ###
+    + optionalString targetPlatform.useBolt ''
+      echo " --emit-relocs" >> $out/nix-support/cc-ldflags
+    ''
+
     ##
     ## Extra custom steps
     ##

pkgs/development/compilers/llvm/common/bolt/default.nix

@@ -12,6 +12,7 @@
   libclang,
   version,
   python3,
+  substituteAll,
   buildLlvmTools,
   patches ? [ ],
   devExtraCmakeFlags ? [ ],
@@ -71,13 +72,21 @@ stdenv.mkDerivation (finalAttrs: {
   postInstall = ''
     mkdir -p $dev/lib
     mv $out/lib/libLLVMBOLT*.a $dev/lib
+
+    mkdir -p $out/nix-support
+    cp $setupHook $out/nix-support/setup-hook
   '';
 
   outputs = [
     "out"
     "dev"
   ];
 
+  setupHook = substituteAll {
+    src = ./setup-hook.sh.in;
+    env.readelf = lib.getExe' libllvm "llvm-readelf";
+  };
+
   meta = llvm_meta // {
     homepage = "https://github.com/llvm/llvm-project/tree/main/bolt";
     description = "LLVM post-link optimizer.";

pkgs/development/compilers/llvm/common/bolt/setup-hook.sh.in

@@ -0,0 +1,16 @@
+# shellcheck shell=bash
+
+function boltFixupPhase {
+  local i
+  while IFS= read -r -d $'\0' i; do
+    if ! isELF "$i"; then continue; fi
+    if ! @readelf@ --program-headers "$i" | grep -q LOAD; then continue; fi
+
+    llvm-bolt "$i" -o $(dirname "$i")/.bolt-$(basename "$i") "${boltFlags[@]-}"
+    mv $(dirname "$i")/.bolt-$(basename "$i") "$i"
+  done < <(find "$prefix" -type f -print0)
+}
+
+if [ -z "${dontUseBolt-}" ]; then
+    appendToVar preFixupPhases boltFixupPhase
+fi

pkgs/development/libraries/glibc/common.nix

@@ -349,4 +349,7 @@ stdenv.mkDerivation (
         }
         // (args.meta or { });
     }
+  // lib.optionalAttrs stdenv.hostPlatform.useBolt {
+    dontUseBolt = stdenv.cc.isGNU;
+  }
 )

pkgs/stdenv/cross/default.nix

@@ -69,6 +69,9 @@ lib.init bootStages
           extraNativeBuildInputs =
             old.extraNativeBuildInputs
             ++ lib.optionals (hostPlatform.isLinux && !buildPlatform.isLinux) [ buildPackages.patchelf ]
+            ++ lib.optionals hostPlatform.useBolt [
+              buildPackages.llvmPackages.bolt
+            ]
             ++ lib.optional (
               let
                 f =

pkgs/top-level/release-attrpaths-superset.nix

@@ -51,6 +51,7 @@ let
     # cross packagesets
     pkgsLLVM = true;
     pkgsLLVMLibc = true;
+    pkgsBolt = true;
     pkgsMusl = true;
     pkgsStatic = true;
     pkgsCross = true;

pkgs/top-level/release.nix

@@ -345,6 +345,7 @@ let
       agdaPackages = packagePlatforms pkgs.agdaPackages;
 
       pkgsLLVM.stdenv = [ "x86_64-linux" "aarch64-linux" ];
+      pkgsBolt.stdenv = [ "x86_64-linux" "aarch64-linux" ];
       pkgsLLVMLibc.stdenv = [ "x86_64-linux" "aarch64-linux" ];
       pkgsArocc.stdenv = [ "x86_64-linux" "aarch64-linux" ];
       pkgsZig.stdenv = [ "x86_64-linux" "aarch64-linux" ];

pkgs/top-level/stage.nix

@@ -211,6 +211,20 @@ let
       };
     };
 
+    pkgsBolt = nixpkgsFun {
+      overlays = [
+        (self': super': {
+          pkgsBolt = super';
+        })
+      ] ++ overlays;
+      # Bootstrap a cross stdenv and apply the Bolt post-link optimizer.
+      # This is currently not possible when compiling natively,
+      # so we don't need to check hostPlatform != buildPlatform.
+      crossSystem = stdenv.hostPlatform // {
+        useBolt = true;
+      };
+    };
+
     pkgsLLVMLibc = nixpkgsFun {
       overlays = [ (self': super': {
         pkgsLLVMLibc = super';