RISC-V GNU Compiler Toolchain

This is the RISC-V C and C++ cross-compiler. It supports two build modes: a generic ELF/Newlib toolchain and a more sophisticated Linux-ELF/glibc toolchain.

Getting the sources

This repository uses submodules, but submodules will fetch automatically on demand, so --recursive or git submodule update --init --recursive is not needed.

$ git clone https://github.com/riscv/riscv-gnu-toolchain

Warning: git clone takes around 6.65 GB of disk and download size

Prerequisites

Several standard packages are needed to build the toolchain.

On Ubuntu, executing the following command should suffice:

$ sudo apt-get install autoconf automake autotools-dev curl python3 libmpc-dev libmpfr-dev libgmp-dev gawk build-essential bison flex texinfo gperf libtool patchutils bc zlib1g-dev libexpat-dev

On Fedora/CentOS/RHEL OS, executing the following command should suffice:

$ sudo yum install autoconf automake python3 libmpc-devel mpfr-devel gmp-devel gawk  bison flex texinfo patchutils gcc gcc-c++ zlib-devel expat-devel

On Arch Linux, executing the following command should suffice:

$ pacman -Syyu autoconf automake curl python3 mpc mpfr gmp gawk base-devel bison flex texinfo gperf libtool patchutils bc zlib expat

On OS X, you can use Homebrew to install the dependencies:

$ brew install python3 gawk gnu-sed gmp mpfr libmpc isl zlib expat
$ brew tap discoteq/discoteq
$ brew install flock

To build the glibc (Linux) on OS X, you will need to build within a case-sensitive file system. The simplest approach is to create and mount a new disk image with a case sensitive format. Make sure that the mount point does not contain spaces. This is not necessary to build newlib or gcc itself on OS X.

This process will start by downloading about 200 MiB of upstream sources, then will patch, build, and install the toolchain. If a local cache of the upstream sources exists in $(DISTDIR), it will be used; the default location is /var/cache/distfiles. Your computer will need about 8 GiB of disk space to complete the process.

Installation (Newlib)

To build the Newlib cross-compiler, pick an install path. If you choose, say, /opt/riscv, then add /opt/riscv/bin to your PATH now. Then, simply run the following command:

./configure --prefix=/opt/riscv
make

You should now be able to use riscv64-unknown-elf-gcc and its cousins.

Installation (Linux)

To build the Linux cross-compiler, pick an install path. If you choose, say, /opt/riscv, then add /opt/riscv/bin to your PATH now. Then, simply run the following command:

./configure --prefix=/opt/riscv
make linux

The build defaults to targetting RV64GC (64-bit), even on a 32-bit build environment. To build the 32-bit RV32GC toolchain, use:

./configure --prefix=/opt/riscv --with-arch=rv32gc --with-abi=ilp32d
make linux

Supported architectures are rv32i or rv64i plus standard extensions (a)tomics, (m)ultiplication and division, (f)loat, (d)ouble, or (g)eneral for MAFD.

Supported ABIs are ilp32 (32-bit soft-float), ilp32d (32-bit hard-float), ilp32f (32-bit with single-precision in registers and double in memory, niche use only), lp64 lp64f lp64d (same but with 64-bit long and pointers).

Installation (Newlib/Linux multilib)

To build either cross-compiler with support for both 32-bit and 64-bit, run the following command:

./configure --prefix=/opt/riscv --enable-multilib

And then either make or make linux for the Newlib or Linux cross-compiler respectively.

The multilib compiler will have the prefix riscv64-unknown-elf- or riscv64-unknown-linux-gnu-, but will be able to target both 32-bit and 64-bit systems. It will support the most common -march/-mabi options, which can be seen by using the --print-multi-lib flag on either cross-compiler.

Troubleshooting Build Problems

Builds work best if installing into an empty directory. If you build a hard-float toolchain and then try to build a soft-float toolchain with the same --prefix directory, then the build scripts may get confused and exit with a linker error complaining that hard float code can't be linked with soft float code. Removing the existing toolchain first, or using a different prefix for the second build, avoids the problem. It is OK to build one newlib and one linux toolchain with the same prefix. But you should avoid building two newlib or two linux toolchains with the same prefix.

If building a linux toolchain on a MacOS system, or on a Windows system using the Linux subsystem or cygwin, you must ensure that the filesystem is case-sensitive. A build on a case-insensitive filesystem will fail when building glibc because *.os and *.oS files will clobber each other during the build eventually resulting in confusing link errors.

Centos (and RHEL) provide old GNU tools versions that may be too old to build a RISC-V toolchain. There is an alternate toolset provided that includes current versions of the GNU tools. This is the devtoolset provided as part of the Software Collection service. For more info, see the devtoolset-7 URL. There are various versions of the devtoolset that are available, so you can also try other versions of it, but we have at least one report that devtoolset-7 works.

Advanced Options

There are a number of additional options that may be passed to configure. See './configure --help' for more details.

Build with customized multi-lib configure.

--with-multilib-generator= can specify what multilibs to build. The argument is a semicolon separated list of values, possibly consisting of a single value. Currently only supported for riscv--elf*. The accepted values and meanings are given below.

Every config is constructed with four components: architecture string, ABI, reuse rule with architecture string and reuse rule with sub-extension.

Re-use part support expansion operator (*) to simplify the combination of different sub-extensions, example 4 demonstrate how it uses and works.

Example 1: Add multi-lib support for rv32i with ilp32.

./configure --with-multilib-generator="rv32i-ilp32--"

Example 2: Add multi-lib support for rv32i with ilp32 and rv32imafd with ilp32.

./configure --with-multilib-generator="rv32i-ilp32--;rv32imafd-ilp32--"

Example 3: Add multi-lib support for rv32i with ilp32; rv32im with ilp32 and rv32ic with ilp32 will reuse this multi-lib set.

./configure --with-multilib-generator="rv32i-ilp32-rv32im-c"

Example 4: Add multi-lib support for rv64ima with lp64; rv64imaf with lp64, rv64imac with lp64 and rv64imafc with lp64 will reuse this multi-lib set.

./configure --with-multilib-generator="rv64ima-lp64--f*c"

Test Suite

The Dejagnu test suite has been ported to RISC-V. This can be run with a simulator for the elf and linux toolchains. The simulator can be selected by the SIM variable in the Makefile, e.g. SIM=qemu, SIM=gdb, or SIM=spike (experimental). However, the testsuite allowlist is only mintained for qemu. Other simulators might get extra failures. To test GCC, run the following commands:

./configure --prefix=$RISCV --disable-linux --with-arch=rv64ima # or --with-arch=rv32ima
make newlib
make report-newlib SIM=gdb # Run with gdb simulator

./configure --prefix=$RISCV
make linux
make report-linux SIM=qemu # Run with qemu

Note:

• spike only support rv64* bare-metal/elf toolchain.
• gdb simulator only support bare-metal/elf toolchain.

Development

This section is only for developer or advanced user, or you want to build toolchain with your own source tree.

Update Source Tree

riscv-gnu-toolchain contain stable but not latest source for each submodule, in case you want to using latest develoment tree, you can use following command to upgrade all submodule.

git submodule update --remote

Or you can upgrade specific submodule only.

git submodule update --remote <component>

For example, upgrade riscv-gcc only, you can using following command:

git submodule update --remote riscv-gcc

How to Check Which Branch are Used for Specific submodule

The branch info has recorded in .gitmodules file, which can set or update via git submodule add -b or git submodule set-branch.

However the only way to check which branch are using is to check .gitmodules file, here is the example for riscv-gcc, it using riscv-gcc-10.2.0 branch, so it will has a section named riscv-gcc and has a field branch is riscv-gcc-10.2.0.

[submodule "riscv-gcc"]
        path = riscv-gcc
        url = ../riscv-gcc.git
        branch = riscv-gcc-10.2.0

Use Source Tree Other Than riscv-gnu-toolchain

riscv-gnu-toolchain also support using out-of-tree source to build toolchain, there is couple configure option to specify the source tree of each submodule/component.

For example you have a gcc in $HOME/gcc, use --with-gcc-src can specify that:

./configure --with-gcc-src=$HOME/gcc

Here is the list of configure option for specify source tree:

--with-gcc-src
--with-binutils-src
--with-newlib-src
--with-glibc-src
--with-musl-src
--with-gdb-src
--with-linux-headers-src