Note: This isn’t intended to replace the official Checking out and building Chromium on Linux guide.

1. Prepare tools

First, install tools that are directly available for download.

$ sudo pacman -S --needed base-devel direnv git clang lld ninja ccache rustup rust-bindgen rustfmt
$ rustup default nightly

Then, build and install the following AURs:

  • python311: No modifications to PKGBUILD are needed, apart from appending loong64 to arch.
  • gn-git: As of this writing, the built GN version is r2599.f90c3d9df. Edit PKGBUILD so that only target gn is built. The diff to PKGBUILD should look like the following:
diff --git a/PKGBUILD b/PKGBUILD
index 38d46f408f2369b38b262c90a4c827d9497485ef..17b12e5f4ff7cffd4072d2b9342f1d7e2c2768be 100644
--- a/PKGBUILD
+++ b/PKGBUILD
@@ -3,10 +3,10 @@

 pkgname=gn-git
 pkgdesc='Meta-build system which generates Ninja build files'
-pkgver=r1682.a5bcbd72
+pkgver=r2599.f90c3d9df
 pkgrel=1
 license=('BSD')
-arch=('x86_64' 'i686')
+arch=('x86_64' 'i686' 'loong64')
 conflicts=(gn-bin gn)
 provides=(gn)
 depends=(gcc-libs)
@@ -23,17 +23,16 @@ pkgver () {

 prepare () {
        cd gn
-       patch -p1 < "${srcdir}/gcc-support.patch"
+       patch -Np1 -i "${srcdir}/gcc-support.patch"
 }

 build () {
        cd gn
-       CC=cc CXX=c++ AR=ar \
        CFLAGS="${CFLAGS} -pthread" \
        CXXFLAGS="${CXXFLAGS} -pthread" \
        LDFLAGS="${LDFLAGS} -pthread" \
                python build/gen.py --use-lto --no-strip
-       ninja -C out
+       ninja -C out gn
 }

 package () {

2. Set up workspace directory

Make an empty directory for containing all our future works. Let’s name it google-source.

$ mkdir google-source
$ cd google-source

From now on, make sure that you have cd‘ed into google-source, or the workspace directory you choose.

3. Install depot_tools

$ git clone https://chromium.googlesource.com/chromium/tools/depot_tools.git

This is not directly usable. We also need to set up various environment variables for it to work.

First, create a Python 3.11 venv, and install dependencies required by V8 according to v8/vpython.toml:

$ mkdir venv
$ /usr/bin/python3.11 -m venv venv/depot_tools
$ ./venv/depot_tools/bin/pip install six==1.15.0 coverage==7.3.1 pbr==3.0.0 filecheck==1.0.1 funcsigs==1.0.2 mock==2.0.0 setuptools==68.0.0 numpy==1.23.5 protobuf==3.19.3 requests==2.31.0 urllib3==1.26.6 idna==2.8 certifi==2020.11.8 charset-normalizer==2.0.4 pyfakefs==5.7.3

The versions are to be derived from vpython.toml when you check out your own copy of V8.

Then, create an .envrc containing the following:

prepend_path () {
    case ":$PATH:" in
        *:"$1":*)
            ;;
        *)
            export PATH="$1:${PATH}"
            ;;
    esac
}

prepend_path "$(pwd)"/depot_tools

export GIT_CONFIG_COUNT=2
export GIT_CONFIG_KEY_0='core.autocrlf'
export GIT_CONFIG_VALUE_0='false'
export GIT_CONFIG_KEY_1='core.filemode'
export GIT_CONFIG_VALUE_1='false'

export VPYTHON_BYPASS='manually managed python not supported by chrome operations'
export DEPOT_TOOLS_BOOTSTRAP_PYTHON3=0

. ./venv/depot_tools/bin/activate

Run direnv allow to make it effective. This activates our Python 3.11 venv for depot_tools whenever we cd into our workspace. Also, we use the GIT_CONFIG_* family of environment variables to apply Git configurations required by V8, so that our global configuration wouldn’t be contaminated.

4. Fetch the source

Make an empty directory to contain our V8 checkout, let’s name it “v8”. Then run fetch.

$ mkdir v8
$ cd v8
$ fetch v8

This will fail midway. Ignore the failure. We’ll fix it up soon™.

5. Apply vendored tool patches

V8 intends to make builds reproducible by vendoring all tools. This isn’t possible on Loong64, since most tools don’t have Loong64 builds ready in Google’s servers. We need to gate them away to prevent fetching failures.

diff --git a/.gn b/.gn
index fcc0c855322ef64d77611216783e10d70e8915f9..75e8108785092d5da399cd2a795013bd42948566 100644
--- a/.gn
+++ b/.gn
@@ -9,7 +9,7 @@ buildconfig = "//build/config/BUILDCONFIG.gn"
 
 # The hermetic Python interpreter to use by default. Platforms without a
 # hermetic CPython CIPD package fallback to the system python3 on $PATH.
-if (host_cpu == "s390x" || host_cpu == "ppc64" || host_os == "zos") {
+if (host_cpu == "s390x" || host_cpu == "ppc64" || host_os == "zos" || host_cpu == "loong64") {
   script_executable = "python3"
 } else {
   script_executable = "//third_party/cpython3/host/bin/python3"
diff --git a/DEPS b/DEPS
index 743e15833fba4771044d76ac47fab6298bfb9032..63d68e6e6a2c87da427a48c893fd0d9258dc3d8e 100644
--- a/DEPS
+++ b/DEPS
@@ -172,7 +172,7 @@ deps = {
       }
     ],
     'dep_type': 'cipd',
-    'condition': 'host_os == "linux" and host_cpu != "s390x" and host_os != "zos" and host_cpu != "ppc64"',
+    'condition': 'host_os == "linux" and host_cpu != "s390x" and host_os != "zos" and host_cpu != "ppc64" and host_cpu != "loong64"',
   },
   'buildtools/mac': {
     'packages': [
@@ -202,7 +202,7 @@ deps = {
       }
     ],
     'dep_type': 'cipd',
-    'condition': '(host_os == "linux" or host_os == "mac" or host_os == "win") and host_cpu != "s390x" and host_os != "zos" and host_cpu != "ppc64" and (host_cpu != "arm64" or host_os == "mac")',
+    'condition': '(host_os == "linux" or host_os == "mac" or host_os == "win") and host_cpu != "s390x" and host_os != "zos" and host_cpu != "ppc64" and (host_cpu != "arm64" or host_os == "mac") and host_cpu != "loong64"',
   },
   # TODO(498118202): Use checkout_benchmarks here too.
   'test/benchmarks/data':
@@ -363,7 +363,7 @@ deps = {
         'sha256sum': 'ab8ec1e75c7f74565e9f893212262780abc9174363ce5f1ff670c415e9cd4147',
         'size_bytes': 57258740,
         'generation': 1791353523054521,
-        'condition': 'host_os == "linux"',
+        'condition': 'host_os == "linux" and host_cpu == "x64"',
       },
       {
         'object_name': 'Linux_x64/clang-tidy-llvmorg-24-init-7747-g62397f8b-67.tar.xz',
@@ -391,7 +391,7 @@ deps = {
         'sha256sum': 'c575a16aa6516a47ad58c6f66ea604d3ec183d9b7a6ca72139b10d01a3ade984',
         'size_bytes': 5924452,
         'generation': 1791353523760046,
-        'condition': '(checkout_linux or checkout_mac or checkout_android) and host_os == "linux"',
+        'condition': '(checkout_linux or checkout_mac or checkout_android) and host_os == "linux" and host_cpu == "x64"',
       },
       {
         'object_name': 'Mac/clang-llvmorg-24-init-7747-g62397f8b-67.tar.xz',
@@ -526,7 +526,7 @@ deps = {
       }
     ],
     'dep_type': 'cipd',
-    'condition': 'host_cpu != "s390x" and host_os != "zos" and host_cpu != "ppc64"'
+    'condition': 'host_cpu != "s390x" and host_os != "zos" and host_cpu != "ppc64" and host_cpu != "loong64"'
   },
   'third_party/partition_alloc': {
     'url': Var('chromium_url') + '/chromium/src/base/allocator/partition_allocator.git@' + Var('partition_alloc_version'),
@@ -557,7 +557,7 @@ deps = {
         'sha256sum': '6287ecced3bc5113122a88dbe15c910edec0828718423a67529c24de0f060e98',
         'size_bytes': 287212360,
         'generation': 1791299089231058,
-        'condition': 'host_os == "linux"',
+        'condition': 'host_os == "linux" and host_cpu == "x64"',
       },
       {
         'object_name': 'Mac/rust-toolchain-1edd55dcfcd573872c727fa3e086369a71661ee0-1125-llvmorg-24-init-7747-g62397f8b.tar.xz',
@@ -600,7 +600,7 @@ deps = {
         'sha256sum': '1472e8a5cfc4959f94ff18aa5ec864b07991d877995a563eeb4176e344a7fa59',
         'size_bytes': 22761568,
         'generation': 1791299091145399,
-        'condition': 'host_os == "linux"',
+        'condition': 'host_os == "linux" and host_cpu == "x64"',
       },
       {
         'object_name': 'Mac/rust-libclang-1edd55dcfcd573872c727fa3e086369a71661ee0-1125-llvmorg-24-init-7747-g62397f8b.tar.xz',
@@ -643,7 +643,7 @@ deps = {
         'version': Var('cpython3_version'),
       }
     ],
-    'condition': 'not build_with_chromium and host_cpu != "s390x" and host_os != "zos" and host_cpu != "ppc64"',
+    'condition': 'not build_with_chromium and host_cpu != "s390x" and host_os != "zos" and host_cpu != "ppc64" and host_cpu != "loong64"',
     'dep_type': 'cipd',
   },
   # Host platform package.
@@ -654,7 +654,7 @@ deps = {
         'version': Var('cpython3_version'),
       }
     ],
-    'condition': 'not build_with_chromium and host_cpu != "s390x" and host_os != "zos" and host_cpu != "ppc64"',
+    'condition': 'not build_with_chromium and host_cpu != "s390x" and host_os != "zos" and host_cpu != "ppc64" and host_cpu != "loong64"',
     'dep_type': 'cipd',
   },
   'third_party/zlib':

Note that exact lines might differ from your checkout thanks to time differences, but the idea holds.

After patching, re-sync the tree:

$ # In google-source/v8
$ gclient sync

6. Configuration

$ ARGS=(
>   'is_clang=true'
>   'clang_base_path="/usr"'
>   'clang_use_chrome_plugins=false'
>   'use_sysroot=false'
>   'use_lld=true'
>   'is_debug=true'
>   'symbol_level=2'
>   'v8_optimized_debug=true'
>   'clang_version="23"'
>   'treat_warnings_as_errors=false'
>   'rust_sysroot_absolute="/home/csmantle/.rustup/toolchains/nightly-loongarch64-unknown-linux-gnu"'
>   'rust_bindgen_root="/usr"'
>   'v8_metagen_libclang_so="/usr/lib/libclang.so"'
>   'v8_metagen_libclang_bindings_dir="/home/csmantle/workspace/google-source/v8/v8/third_party/llvm-libclang/bindings/python"'
> )
$ gn gen out/loong64.debug --args="${ARGS[*]}"

Adjust clang_version= to your system’s Clang version. Also adjust paths accordingly.

7. Generate compile_commands.json

$ tools/clang/scripts/generate_compdb.py -p out/loong64.debug >compile_commmands.json

Congratulations! You now have a working environment for V8 development.

8. Build and test

$ ninja -C out/loong64.debug
$ tools/run-tests.py --outdir=out/loong64.debug