diff --git a/src/build.sh b/src/build.sh
new file mode 100755
index 0000000000..06132e47ed
--- /dev/null
+++ b/src/build.sh
@@ -0,0 +1,101 @@
+#!/bin/sh
+set -e
+
+export TMPDIR="$PWD/tmp"
+rm -rf "$TMPDIR"
+mkdir -p "$TMPDIR"
+
+if [ "$1" = debug ]; then
+  out=out/Debug
+  flags="
+    is_debug=true
+    is_component_build=true"
+else
+  out=out/Release
+  flags="
+    is_official_build=true
+    exclude_unwind_tables=true
+    enable_resource_allowlist_generation=false
+    symbol_level=0"
+fi
+
+. ./get-sysroot.sh
+
+# ccache
+case "$host_os" in
+  linux|mac)
+    if which ccache >/dev/null 2>&1; then
+      export CCACHE_SLOPPINESS=time_macros
+      export CCACHE_BASEDIR="$PWD"
+      export CCACHE_CPP2=yes
+      CCACHE=ccache
+    fi
+  ;;
+  win)
+    if [ -f "$HOME"/.cargo/bin/sccache* ]; then
+      export PATH="$PATH:$HOME/.cargo/bin"
+      CCACHE=sccache
+    fi
+  ;;
+esac
+if [ "$CCACHE" ]; then
+  flags="$flags
+    cc_wrapper=\"$CCACHE\""
+fi
+
+flags="$flags"'
+  is_clang=true
+  use_sysroot=false
+
+  fatal_linker_warnings=false
+  treat_warnings_as_errors=false
+
+  enable_base_tracing=false
+  use_udev=false
+  use_aura=false
+  use_ozone=false
+  use_gio=false
+  use_gtk=false
+  use_platform_icu_alternatives=true
+  use_glib=false
+
+  disable_file_support=true
+  enable_websockets=false
+  use_kerberos=false
+  enable_mdns=false
+  enable_reporting=false
+  include_transport_security_state_preload_list=false
+  use_nss_certs=false
+
+  enable_backup_ref_ptr_support=false
+  enable_dangling_raw_ptr_checks=false
+'
+
+if [ "$WITH_SYSROOT" ]; then
+  flags="$flags
+    target_sysroot=\"//$WITH_SYSROOT\""
+fi
+
+if [ "$host_os" = "mac" ]; then
+  flags="$flags"'
+    enable_dsyms=false'
+fi
+
+case "$EXTRA_FLAGS" in
+*target_os=\"android\"*)
+  # default_min_sdk_version=24: 26 introduces unnecessary snew symbols
+  # is_high_end_android=true: Does not optimize for size, Uses PGO profiles
+  flags="$flags"'
+    default_min_sdk_version=24
+    is_high_end_android=true'
+  ;;
+esac
+
+rm -rf "./$out"
+mkdir -p out
+
+export DEPOT_TOOLS_WIN_TOOLCHAIN=0
+
+./gn/out/gn gen "$out" --args="$flags $EXTRA_FLAGS" --script-executable=$PYTHON
+
+ninja -C "$out" naive
diff --git a/src/get-clang.sh b/src/get-clang.sh
new file mode 100755
index 0000000000..ddf7365d5a
--- /dev/null
+++ b/src/get-clang.sh
@@ -0,0 +1,111 @@
+#!/bin/sh
+set -ex
+
+. ./get-sysroot.sh
+
+if [ "$SYSROOT_ARCH" -a ! -d ./"$WITH_SYSROOT/lib" ]; then
+  ./build/linux/sysroot_scripts/sysroot_creator.py build "$SYSROOT_ARCH"
+fi
+
+if [ "$OPENWRT_FLAGS" ]; then
+  ./get-openwrt.sh
+fi
+
+# Clang
+# See src/tools/clang/scripts/update.py
+case "$host_os" in
+  linux) WITH_CLANG=Linux_x64;;
+  win) WITH_CLANG=Win;;
+  mac) WITH_CLANG=Mac;;
+esac
+if [ "$host_os" = mac -a "$host_cpu" = arm64 ]; then
+  WITH_CLANG=Mac_arm64
+fi
+mkdir -p third_party/llvm-build/Release+Asserts
+cd tools/clang/scripts
+CLANG_REVISION=$($PYTHON -c 'import update; print(update.PACKAGE_VERSION)')
+cd -
+echo $CLANG_REVISION >third_party/llvm-build/Release+Asserts/cr_build_revision
+if [ ! -d third_party/llvm-build/Release+Asserts/bin ]; then
+  mkdir -p third_party/llvm-build/Release+Asserts
+  clang_path="clang-$CLANG_REVISION.tgz"
+  clang_url="https://commondatastorage.googleapis.com/chromium-browser-clang/$WITH_CLANG/$clang_path"
+  curl "$clang_url" | tar xzf - -C third_party/llvm-build/Release+Asserts
+fi
+
+# sccache
+if [ "$host_os" = win -a ! -f ~/.cargo/bin/sccache.exe ]; then
+  sccache_url="https://github.com/mozilla/sccache/releases/download/0.2.12/sccache-0.2.12-x86_64-pc-windows-msvc.tar.gz"
+  mkdir -p ~/.cargo/bin
+  curl -L "$sccache_url" | tar xzf - --strip=1 -C ~/.cargo/bin
+fi
+
+# GN
+# See src/DEPS
+case "$host_os" in
+  linux) WITH_GN=linux-amd64;;
+  win) WITH_GN=windows-amd64;;
+  mac) WITH_GN=mac-amd64;;
+esac
+if [ "$host_os" = mac -a "$host_cpu" = arm64 ]; then
+  WITH_GN=mac-arm64
+fi
+if [ ! -f gn/out/gn ]; then
+  gn_version=$(grep "'gn_version':" DEPS | cut -d"'" -f4)
+  mkdir -p gn/out
+  curl -L "https://chrome-infra-packages.appspot.com/dl/gn/gn/$WITH_GN/+/$gn_version" -o gn.zip
+  unzip gn.zip -d gn/out
+  rm gn.zip
+fi
+
+# See src/build/config/compiler/pgo/BUILD.gn
+case "$target_os" in
+  win)
+    case "$target_cpu" in
+      arm64) WITH_PGO=win-arm64;;
+      x64) WITH_PGO=win64;;
+      *) WITH_PGO=win32;;
+    esac
+  ;;
+  mac)
+    case "$target_cpu" in
+      arm64) WITH_PGO=mac-arm;;
+      *) WITH_PGO=mac;;
+    esac
+  ;;
+  linux|openwrt)
+    WITH_PGO=linux
+  ;;
+  android)
+    case "$target_cpu" in
+      arm64) WITH_PGO=android-arm64;;
+      *) WITH_PGO=android-arm32;;
+    esac
+  ;;
+esac
+if [ "$WITH_PGO" ]; then
+  PGO_PATH=$(cat chrome/build/$WITH_PGO.pgo.txt)
+fi
+if [ "$WITH_PGO" -a ! -f chrome/build/pgo_profiles/"$PGO_PATH" ]; then
+  mkdir -p chrome/build/pgo_profiles
+  cd chrome/build/pgo_profiles
+  curl --limit-rate 10M -LO "https://storage.googleapis.com/chromium-optimization-profiles/pgo_profiles/$PGO_PATH"
+  cd ../../..
+fi
+
+if [ "$target_os" = android -a ! -d third_party/android_toolchain/ndk ]; then
+  # https://dl.google.com/android/repository/android-ndk-r25c-linux.zip
+  android_ndk_version=$(grep 'default_android_ndk_version = ' build/config/android/config.gni | cut -d'"' -f2)
+  curl -LO https://dl.google.com/android/repository/android-ndk-$android_ndk_version-linux.zip
+  unzip android-ndk-$android_ndk_version-linux.zip
+  mkdir -p third_party/android_toolchain/ndk
+  cd android-ndk-$android_ndk_version
+  cp -r --parents sources/android/cpufeatures ../third_party/android_toolchain/ndk
+  cp -r --parents toolchains/llvm/prebuilt ../third_party/android_toolchain/ndk
+  cd ..
+  cd third_party/android_toolchain/ndk
+  find toolchains -type f -regextype egrep \! -regex \
+    '.*(lib(atomic|gcc|gcc_real|compiler_rt-extras|android_support|unwind).a|crt.*o|lib(android|c|dl|log|m).so|usr/local.*|usr/include.*)' -delete
+  cd -
+  rm -rf android-ndk-$android_ndk_version android-ndk-$android_ndk_version-linux.zip
+fi
diff --git a/src/get-openwrt.sh b/src/get-openwrt.sh
new file mode 100755
index 0000000000..4ae0056172
--- /dev/null
+++ b/src/get-openwrt.sh
@@ -0,0 +1,55 @@
+#!/bin/sh
+
+set -ex
+
+eval "$OPENWRT_FLAGS"
+
+sysroot=$PWD/out/sysroot-build/openwrt/$release/$arch
+if [ -d $sysroot/lib ]; then
+  exit 0
+fi
+mkdir -p $sysroot
+
+case "$arch" in
+arm_*) abi=musl_eabi;;
+*) abi=musl;;
+esac
+
+if [ "$subtarget" ]; then
+  SDK_PATH=openwrt-toolchain-$release-$target-${subtarget}_gcc-${gcc_ver}_${abi}.Linux-x86_64
+else
+  subtarget='generic'
+  SDK_PATH=openwrt-toolchain-$release-${target}_gcc-${gcc_ver}_${abi}.Linux-x86_64
+fi
+SDK_URL=https://downloads.openwrt.org/releases/$release/targets/$target/$subtarget/$SDK_PATH.tar.xz
+rm -rf $SDK_PATH
+curl $SDK_URL | tar xJf -
+cd $SDK_PATH
+full_root=toolchain-*_gcc-${gcc_ver}_${abi}
+cat >include.txt <<EOF
+./include
+./lib/*.o
+./lib/gcc/*/libgcc.a
+./lib/gcc/*/libgcc_eh.a
+./lib/libatomic.so*
+./lib/libatomic.a
+./lib/libc.so
+./lib/libc.a
+./lib/libdl.a
+./lib/ld-*
+./lib/libgcc_s.*
+./lib/libm.a
+./lib/libpthread.a
+./lib/libresolv.a
+./lib/librt.a
+./usr
+EOF
+tar cf - -C $full_root --hard-dereference . | tar xf - -C $sysroot --wildcards --wildcards-match-slash -T include.txt
+rm -rf include.txt
+cd ..
+rm -rf $SDK_PATH
+
+# LLVM does not accept muslgnueabi as the target triple environment
+if [ -d "$sysroot/lib/gcc/arm-openwrt-linux-muslgnueabi" ]; then
+  mv "$sysroot/lib/gcc/arm-openwrt-linux-muslgnueabi" "$sysroot/lib/gcc/arm-openwrt-linux-musleabi"
+fi
diff --git a/src/get-sysroot.sh b/src/get-sysroot.sh
new file mode 100644
index 0000000000..ae9a98e8b2
--- /dev/null
+++ b/src/get-sysroot.sh
@@ -0,0 +1,66 @@
+eval "$EXTRA_FLAGS"
+
+case "$(uname)" in
+  MINGW*|MSYS*) host_os=win;;
+  Linux) host_os=linux;;
+  Darwin) host_os=mac;;
+  *) echo "Unsupported host OS" >&2; exit 1;;
+esac
+
+case "$(uname -m)" in
+  x86_64|x64) host_cpu=x64;;
+  x86|i386|i686) host_cpu=x86;;
+  arm) host_cpu=arm;;
+  arm64|aarch64|armv8b|armv8l) host_cpu=arm64;;
+  *) echo "Unsupported host CPU" >&2; exit 1;;
+esac
+
+# See src/build/config/BUILDCONFIG.gn
+if [ ! "$target_os" ]; then
+  target_os="$host_os"
+fi
+
+if [ ! "$target_cpu" ]; then
+  target_cpu="$host_cpu"
+fi
+
+PYTHON=$(which python3 2>/dev/null || which python 2>/dev/null)
+
+# sysroot
+case "$target_os" in
+  linux)
+    case "$target_cpu" in
+      x64) SYSROOT_ARCH=amd64;;
+      x86) SYSROOT_ARCH=i386;;
+      arm64) SYSROOT_ARCH=arm64;;
+      arm) SYSROOT_ARCH=armhf;;
+      mipsel) SYSROOT_ARCH=mipsel;;
+      mips64el) SYSROOT_ARCH=mips64el;;
+      riscv64) SYSROOT_ARCH=riscv64;;
+    esac
+    if [ "$SYSROOT_ARCH" ]; then
+      WITH_SYSROOT="out/sysroot-build/bullseye/bullseye_${SYSROOT_ARCH}_staging"
+    fi
+    # This is the case where running ./build.sh without EXTRA_FLAGS
+    # wants to avoid downloading sysroots.
+    if [ ! "$EXTRA_FLAGS" -a "$target_cpu" = "$host_cpu" ]; then
+      SYSROOT_ARCH=
+      WITH_SYSROOT=
+    fi
+  ;;
+  openwrt)
+    eval "$OPENWRT_FLAGS"
+    WITH_SYSROOT="out/sysroot-build/openwrt/$release/$arch"
+  ;;
+  android)
+    WITH_SYSROOT=
+    # https://dl.google.com/android/repository/sys-img/android/sys-img.xml
+    # https://dl.google.com/android/repository/sys-img/google_apis/sys-img.xml
+    case "$target_cpu" in
+      x64) WITH_ANDROID_IMG=x86_64-24_r08;;
+      x86) WITH_ANDROID_IMG=x86-24_r08;;
+      arm64) WITH_ANDROID_IMG=arm64-v8a-24_r07;;
+      arm) WITH_ANDROID_IMG=armeabi-v7a-24_r07;;
+    esac
+  ;;
+esac