From ee19a77f46082b2eefd9ece7ca2222475f720169 Mon Sep 17 00:00:00 2001
From: Tristan Ross <tristan.ross@midstall.com>
Date: Mon, 20 Jan 2025 22:07:17 -0800
Subject: [PATCH] llvmPackages.bolt: add experimental bolt hook

---
 lib/systems/default.nix                          |  2 ++
 pkgs/build-support/cc-wrapper/default.nix        |  8 ++++++++
 .../compilers/llvm/common/bolt/default.nix       |  5 +++++
 .../compilers/llvm/common/bolt/setup-hook.sh     | 16 ++++++++++++++++
 pkgs/stdenv/cross/default.nix                    |  3 +++
 pkgs/top-level/release-attrpaths-superset.nix    |  1 +
 pkgs/top-level/release.nix                       |  1 +
 pkgs/top-level/stage.nix                         | 14 ++++++++++++++
 8 files changed, 50 insertions(+)
 create mode 100644 pkgs/development/compilers/llvm/common/bolt/setup-hook.sh

diff --git a/lib/systems/default.nix b/lib/systems/default.nix
index ec0106a13dacf6..7dff3fd8c67d1c 100644
--- a/lib/systems/default.nix
+++ b/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"
diff --git a/pkgs/build-support/cc-wrapper/default.nix b/pkgs/build-support/cc-wrapper/default.nix
index 8558a9f3d8d26e..3b24742d9a4fe7 100644
--- a/pkgs/build-support/cc-wrapper/default.nix
+++ b/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
     ##
diff --git a/pkgs/development/compilers/llvm/common/bolt/default.nix b/pkgs/development/compilers/llvm/common/bolt/default.nix
index 9bc078df0e4449..a2054fbacdf5f3 100644
--- a/pkgs/development/compilers/llvm/common/bolt/default.nix
+++ b/pkgs/development/compilers/llvm/common/bolt/default.nix
@@ -71,6 +71,9 @@ 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 = [
@@ -78,6 +81,8 @@ stdenv.mkDerivation (finalAttrs: {
     "dev"
   ];
 
+  setupHook = ./setup-hook.sh;
+
   meta = llvm_meta // {
     homepage = "https://github.com/llvm/llvm-project/tree/main/bolt";
     description = "LLVM post-link optimizer.";
diff --git a/pkgs/development/compilers/llvm/common/bolt/setup-hook.sh b/pkgs/development/compilers/llvm/common/bolt/setup-hook.sh
new file mode 100644
index 00000000000000..acee9c84a54d21
--- /dev/null
+++ b/pkgs/development/compilers/llvm/common/bolt/setup-hook.sh
@@ -0,0 +1,16 @@
+# shellcheck shell=bash
+
+function boltFixupPhase {
+  if [ -d "$prefix/bin" ]; then
+    for e in $(find "$prefix/bin" -executable -type f); do
+      if $(file "$e" | cut -f2 -d ':' | grep -q ELF); then
+        llvm-bolt "$e" -o $(dirname "$e")/.bolt-$(basename "$e") "${boltFlags[@]-}"
+        mv $(dirname "$e")/.bolt-$(basename "$e") "$e"
+      fi
+    done
+  fi
+}
+
+if [ -z "${dontUseBolt-}" ]; then
+    appendToVar preFixupPhases boltFixupPhase
+fi
diff --git a/pkgs/stdenv/cross/default.nix b/pkgs/stdenv/cross/default.nix
index 69ea14be5c83d0..eace479b806a81 100644
--- a/pkgs/stdenv/cross/default.nix
+++ b/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 =
diff --git a/pkgs/top-level/release-attrpaths-superset.nix b/pkgs/top-level/release-attrpaths-superset.nix
index c306a64be585e5..e4ee9c6511b76c 100644
--- a/pkgs/top-level/release-attrpaths-superset.nix
+++ b/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;
diff --git a/pkgs/top-level/release.nix b/pkgs/top-level/release.nix
index 97e64f73c510db..a5c0a1b70cfc9a 100644
--- a/pkgs/top-level/release.nix
+++ b/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" ];
diff --git a/pkgs/top-level/stage.nix b/pkgs/top-level/stage.nix
index 64bc2308f6da77..f1ee4df1b297d6 100644
--- a/pkgs/top-level/stage.nix
+++ b/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';