Get the Source

The V8 project uses Google's depot_tools to manage the source code. For this fork, we will first follow the instructions from v8 and use these tools to retrieve all of the required source from the core project. Then we will use git directly to retrieve the branch with the RISC-V port.

Installing depot_tools

Clone the depot_tools repository to your system:

git clone https://chromium.googlesource.com/chromium/tools/depot_tools.git
export PATH=$PATH:/path/to/depot_tools

You may also want to add export PATH=$PATH:/path/to/depot_tools into your shell configuration file (ex. ~/.bashrc) to ensure that this directory is always in your path.

Now, check that depot_tools is correctly installed:

gclient

If this shows the usage information, then your installation is successful.

Checkout V8 Source from Google

Assuming V8_ROOT is defined to some root directory for your v8 work:

mkdir $V8_ROOT
cd $V8_ROOT
fetch v8
cd v8

You can now browse the original v8 code under $V8_ROOT/v8.

Due to an incompatibility between our branch and the current third-party tools that are checked out by the v8 fetch, we need to go in and checkout an older version of buildtools to prevent a build error.

cd /v8/buildtools
git checkout 73414d522630b27aa3b8d8b63e61d0a5c912a35a

Checkout the RISC-V Branch

Since the RISC-V port is not yet upstream, we need to pull it from this repository.

cd $V8_ROOT/v8
git remote add riscv https://github.com/v8-riscv/v8.git
# or alternatively using ssh
git remote add riscv [email protected]:v8-riscv/v8.git
git fetch riscv
git checkout riscv-porting-dev

Patch the Chromium Build Toolchain

Since this port is not yet upstream, we will also need to apply one patch to the build files which have been fetched from a separate repository. Create a file, build.patch, under $V8_ROOT/v8/build with the following contents:

diff --git a/build_config.h b/build_config.h
index d3cdd2db4..18f37cbbb 100644
--- a/build_config.h
+++ b/build_config.h
@@ -166,6 +166,20 @@
 #define ARCH_CPU_32_BITS 1
 #define ARCH_CPU_BIG_ENDIAN 1
 #endif
+#elif defined(__riscv) || defined(__riscv__)
+#if __riscv_xlen == 64
+#define ARCH_CPU_RISCV_FAMILY 1
+#define ARCH_CPU_RISCV64 1
+#define ARCH_CPU_64_BITS 1
+#define ARCH_CPU_LITTLE_ENDIAN 1
+#elif __riscv_xlen == 32
+#define ARCH_CPU_RISCV_FAMILY 1
+#define ARCH_CPU_RISCV32 1
+#define ARCH_CPU_32_BITS 1
+#define ARCH_CPU_LITTLE_ENDIAN 1
+#else
+#error "Cannot detect Riscv's bitwidth"
+#endif
 #else
 #error Please add support for your architecture in build/build_config.h
 #endif
diff --git a/toolchain/linux/BUILD.gn b/toolchain/linux/BUILD.gn
index fa8b17e9d..f275e4dc5 100644
--- a/toolchain/linux/BUILD.gn
+++ b/toolchain/linux/BUILD.gn
@@ -65,6 +65,24 @@ gcc_toolchain("arm") {
   }
 }

+gcc_toolchain("riscv64") {
+  toolprefix = "riscv64-unknown-linux-gnu-"
+
+  cc = "${toolprefix}gcc"
+  cxx = "${toolprefix}g++"
+
+  ar = "${toolprefix}ar"
+  ld = cxx
+  readelf = "${toolprefix}readelf"
+  nm = "${toolprefix}nm"
+
+  toolchain_args = {
+    current_cpu = "riscv64"
+    current_os = "linux"
+    is_clang = false
+  }
+}
+
 clang_toolchain("clang_x86") {
   # Output linker map files for binary size analysis.
   enable_linker_map = true
@@ -136,6 +154,14 @@ clang_toolchain("clang_x64_v8_arm64") {
   }
 }

+clang_toolchain("clang_x64_v8_riscv64") {
+  toolchain_args = {
+    current_cpu = "x64"
+    v8_current_cpu = "riscv64"
+    current_os = "linux"
+  }
+}
+
 clang_toolchain("clang_x64_v8_mips64el") {
   toolchain_args = {
     current_cpu = "x64"

Now, apply this patch:

cd $V8_ROOT/v8/build
git apply build.patch