riscv-tools

This repo provides guides and references:

1. Quickstart

2. The RISC-V GCC/Newlib Toolchain Installation Manual

3. The Linux/RISC-V Installation Manual

4. References

Quickstart

$ git submodule update --init --recursive
$ export RISCV=/path/to/install/riscv/toolchain
$ ./build.sh

Ubuntu packages needed:

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

Fedora packages needed:

$ sudo dnf install autoconf automake @development-tools curl dtc libmpc-devel mpfr-devel gmp-devel gawk build-essential bison flex texinfo gperf libtool patchutils bc zlib-devel

Note: This requires a compiler with C++11 support (e.g. GCC >= 4.8). To use a compiler different than the default, use:

$ CC=gcc-5 CXX=g++-5 ./build.sh

Note for OS X: We recommend using Homebrew to install the dependencies (dtc gawk gnu-sed gmp mpfr libmpc isl wget) or even to install the tools directly. This repo will build with Apple's command-line developer tools (clang) in addition to gcc.

The RISC-V GCC/Newlib Toolchain Installation Manual

This document was authored by Quan Nguyen and is a mirrored version (with slight modifications) of the one found at Quan's OCF website. Recent updates were made by Sagar Karandikar.

Last updated August 6, 2014

Introduction

The purpose of this page is to document a procedure through which an interested user can build the RISC-V GCC/Newlib toolchain.

A project with a duration such as this requires adequate documentation to support future development and maintenance. This document is created with the hope of being useful; however, its accuracy is not guaranteed.

This work was completed at Andrew and Yunsup's request.

Table of Contents

1. Introduction
2. Table of Contents
3. Meta-installation Notes
4. Installing the Toolchain
5. Testing Your Toolchain
6. "Help! It doesn't work!"

Meta-installation Notes

You may notice this document strikes you as similar to its bigger sibling, the Linux/RISC-V Installation Manual. That's because the instructions are rather similar. That said...

Running Shell Commands

Instructive text will appear as this paragraph does. Any instruction to execute in your terminal will look like this:

$ echo "execute this"

Optional shell commands that may be required for your particular system will have their prompt preceeded with an O:

O$ echo "call this, maybe"

If you will need to replace a bit of code that applies specifically to your situation, it will be surrounded by [square brackets].

The Standard Build Unit

To instruct how long it will take someone to build the various components of the packages on this page, I have provided build times in terms of the Standard Build Unit (SBU), as coined by Gerard Beekmans in his immensely useful Linux From Scratch website.

On an Intel Xeon Dual Quad-core server with 48 GiB RAM, I achieved the following build time for binutils: 38.64 seconds. Thus, 38.64 seconds = 1 SBU. (EECS members at the University of California, Berkeley: I used the s141.millennium server.)

As a point of reference, my 2007 MacBook with an Intel Core 2 Duo and 1 GiB RAM has 100.1 seconds to each SBU. Building riscv64-unknown-linux-gnu-gcc, unsurprisingly, took about an hour.

Items marked as "optional" are not measured.

Having Superuser Permissions

You will need root privileges to install the tools to directories like /usr/bin, but you may optionally specify a different installation directory. Otherwise, superuser privileges are not necessary.

GCC Version

Note: Building riscv-tools requires GCC >= 4.8 for C++11 support (including thread_local). To use a compiler different than the default (for example on OS X), you'll need to do the following when the guide requires you to run build.sh:

$ CC=gcc-4.8 CXX=g++-4.8 ./build.sh

Installing the Toolchain

Let's start with the directory in which we will install our tools. Find a nice, big expanse of hard drive space, and let's call that $TOP. Change to the directory you want to install in, and then set the $TOP environment variable accordingly:

$ export TOP=$(pwd)

For the sake of example, my $TOP directory is on s141.millennium, at /scratch/quannguyen/noob, named so because I believe even a newbie at the command prompt should be able to complete this tutorial. Here's to you, n00bs!

Tour of the Sources

If we are starting from a relatively fresh install of GNU/Linux, it will be necessary to install the RISC-V toolchain. The toolchain consists of the following components:

• riscv-gnu-toolchain, a RISC-V cross-compiler
• riscv-fesvr, a "front-end" server that services calls between the host and target processors on the Host-Target InterFace (HTIF) (it also provides a virtualized console and disk device)
• riscv-isa-sim, the ISA simulator and "golden standard" of execution
• riscv-opcodes, the enumeration of all RISC-V opcodes executable by the simulator
• riscv-pk, a proxy kernel that services system calls generated by code built and linked with the RISC-V Newlib port (this does not apply to Linux, as it handles the system calls)
• riscv-tests, a set of assembly tests and benchmarks

In the installation guide for Linux builds, we built only the simulator and the front-end server. Binaries built against Newlib with riscv-gnu-toolchain will not have the luxury of being run on a full-blown operating system, but they will still demand to have access to some crucial system calls.

What's Newlib?

Newlib is a "C library intended for use on embedded systems." It has the advantage of not having so much cruft as Glibc at the obvious cost of incomplete support (and idiosyncratic behavior) in the fringes. The porting process is much less complex than that of Glibc because you only have to fill in a few stubs of glue code.

These stubs of code include the system calls that are supposed to call into the operating system you're running on. Because there's no operating system proper, the simulator runs, on top of it, a proxy kernel (riscv-pk) to handle many system calls, like open, close, and printf.

Obtaining and Compiling the Sources (7.87 SBU)

First, clone the tools from the riscv-tools GitHub repository:

$ git clone https://github.com/riscv/riscv-tools.git

This command will bring in only references to the repositories that we will need. We rely on Git's submodule system to take care of resolving the references. Enter the newly-created riscv-tools directory and instruct Git to update its submodules.

$ cd $TOP/riscv-tools
$ git submodule update --init --recursive

To build GCC, we will need several other packages, including flex, bison, autotools, libmpc, libmpfr, and libgmp. Ubuntu distribution installations will require this command to be run. If you have not installed these things yet, then run this:

O$ sudo apt-get install autoconf automake autotools-dev curl device-tree-compiler libmpc-dev libmpfr-dev libgmp-dev gawk build-essential bison flex texinfo gperf libtool patchutils bc

Before we start installation, we need to set the $RISCV environment variable. The variable is used throughout the build script process to identify where to install the new tools. (This value is used as the argument to the --prefix configuration switch.)

$ export RISCV=$TOP/riscv

If your $PATH variable does not contain the directory specified by $RISCV, add it to the $PATH environment variable now:

$ export PATH=$PATH:$RISCV/bin

The number of parallel compiler runs is set by $MAKEFLAGS.

With everything else set up, run the build script. Recall that if you're using a new-version of gcc that isn't the default on your system, you'll need to precede the ./build.sh with CC=gcc-4.8 CXX=g++-4.8:

$ ./build.sh

Testing Your Toolchain

Now that you have a toolchain, it'd be a good idea to test it on the quintessential "Hello world!" program. Exit the riscv-tools directory and write your "Hello world!" program. I'll use a long-winded echo command.

$ cd $TOP
$ echo -e '#include <stdio.h>\n int main(void) { printf("Hello world!\\n"); return 0; }' > hello.c

Then, build your program with riscv64-unknown-elf-gcc.

$ riscv64-unknown-elf-gcc -o hello hello.c

When you're done, you may think to do ./hello, but not so fast. We can't even run spike hello, because our "Hello world!" program involves a system call, which couldn't be handled by our host x86 system. We'll have to run the program within the proxy kernel, which itself is run by spike, the RISC-V architectural simulator. Run this command to run your "Hello world!" program:

$ spike pk hello

The RISC-V architectural simulator, spike, takes as its argument the path of the binary to run. This binary is pk, and is located at $RISCV/riscv-elf/bin/pk. spike finds this automatically. Then, riscv-pk receives as its argument the name of the program you want to run.

Hopefully, if all's gone well, you'll have your program saying, "Hello world!". If not...

"Help! It doesn't work!"

Most of the errors below were seen when trying to build riscv-tools on CentOS linux distribution with nfs file-system.

C++11 is not supported, although gcc is updated

This problem occured due to old OS installation repository. A possible solution for CentOS distribution:

wget http://people.centos.org/tru/devtools-2/devtools-2.repo -O /etc/yum.repos.d/devtools-2.repo
sudo yum upgrade
sudo yum install devtoolset-2-gcc devtoolset-2-binutils devtoolset-2-gcc-c++
scl enable devtoolset-2 bash

Last operation will open a shell. Try to run .build.sh from within this shell.

“error: Building GCC requires GMP 4.2+, MPFR 2.4.0+ and MPC 0.8.0+”

Try the following:

cd <riscv-tools>/riscv-gnu-toolchain/riscv-gcc
contrib/download_prerequisites
sudo yum install gmp gmp-devel mpfr mpfr-devel libmpc libmpc-devel

Also try to follow the instructions of C++11 is not supported.

Build script got stuck on "Installing project riscv-fesvr"

That's a very simple problem of output redirection. The solution is to open the /build.common file and change the following line:

$MAKE install >> build.log

to:

$MAKE install | tee install.log

Then when you run the build script, you will see requests to press y to continue which were hidden before. Just follow the instructions.

The Linux/RISC-V Installation Manual

Introduction

The purpose of this page is to document a procedure through which an interested user can install an executable image of the RISC-V architectural port of the Linux kernel.

A project with a duration such as this requires adequate documentation to support future development and maintenance. This document is created with the hope of being useful; however, its accuracy is not guaranteed.

This document is a mirrored version (with slight modifications) of the one found at Quan's OCF website

Table of Contents

1. Introduction
2. Table of Contents
3. Meta-installation Notes
4. Installing the Toolchain
5. Building the Linux Kernel
6. Building BusyBox
7. Creating a Root Disk Image
8. "Help! It doesn't work!"
9. Optional Commands

Meta-installation Notes

Running Shell Commands

Instructive text will appear as this paragraph does. Any instruction to execute in your terminal will look like this:

$ echo "execute this"                     

Optional shell commands that may be required for your particular system will have their prompt preceeded with an O:

O$ echo "call this, maybe"

When booted into the Linux/RISC-V kernel, and some command is to be run, it will appear as a root prompt (with a # as the prompt):

# echo "run this in linux"

If you will need to replace a bit of code that applies specifically to your situation, it will be surrounded by [square brackets].

The Standard Build Unit

To instruct how long it will take someone to build the various components of the packages on this page, I have provided build times in terms of the Standard Build Unit (SBU), as coined by Gerard Beekmans in his immensely useful Linux from Scratch website.

On an Intel Xeon Dual Quad-core server with 48 GiB RAM, I achieved the following build time for binutils: 38.64 seconds. Thus, 38.64 seconds = 1 SBU. (EECS members at the University of California, Berkeley: I used the s141.millennium server.)

As a point of reference, my 2007 MacBook with an Intel Core 2 Duo and 1 GiB RAM has 100.1 seconds to each SBU. Building riscv64-unknown-linux-gnu-gcc, unsurprisingly, took about an hour.

Items marked as "optional" are not measured.

Having Superuser Permissions

You will need root privileges to install the tools to directories like /usr/bin, but you may optionally specify a different installation directory. Otherwise, superuser privileges are not necessary.

Installing the Toolchain (11.81 + ε SBU)

Let's start with the directory in which we will install our tools. Find a nice, big expanse of hard drive space, and let's call that $TOP. Change to the directory you want to install in, and then set the $TOP environment variable accordingly:

$ export TOP=$(pwd)

For the sake of example, my $TOP directory is on s141.millennium, at /scratch/quannguyen/noob, named so because I believe even a newbie at the command prompt should be able to boot Linux using this tutorial. Here's to you, n00bs!

Installing the RISC-V simulator (0.40 SBU)

If we are starting from a relatively fresh install of GNU/Linux, it will be necessary to install the RISC-V toolchain. The toolchain consists of the following components:

• riscv-gnu-toolchain, a RISC-V cross-compiler
• riscv-fesvr, a "front-end" server that services calls between the host and target processors on the Host-Target InterFace (HTIF) (it also provides a virtualized console and disk device)
• riscv-isa-sim, the ISA simulator and "golden standard" of execution
• riscv-opcodes, the enumeration of all RISC-V opcodes executable by the simulator
• riscv-pk, a proxy kernel that services system calls generated by code built and linked with the RISC-V Newlib port (this does not apply to Linux, as it handles the system calls)
• riscv-tests, a set of assembly tests and benchmarks

In actuality, of this list, we will need to build only riscv-fesvr and riscv-isa-sim. These are the two components needed to simulate RISC-V binaries on the host machine. We will also need to build riscv64-unknown-linux-gnu-gcc, but this involves a little modification of the build procedure for riscv64-unknown-elf-gcc.

First, clone the tools from the riscv GitHub repository:

$ git clone https://github.com/riscv/riscv-tools.git

This command will bring in only references to the repositories that we will need. We rely on Git's submodule system to take care of resolving the references. Enter the newly-created riscv-tools directory and instruct Git to update its submodules.

$ cd $TOP/riscv-tools
$ git submodule update --init --recursive

To build GCC, we will need several other packages, including flex, bison, autotools, libmpc, libmpfr, and libgmp. Ubuntu distribution installations will require this command to be run. If you have not installed these things yet, then run this:

O$ sudo apt-get install autoconf automake autotools-dev curl device-tree-compiler libmpc-dev libmpfr-dev libgmp-dev gawk build-essential bison flex texinfo gperf

Before we start installation, we need to set the $RISCV environment variable. The variable is used throughout the build script process to identify where to install the new tools. (This value is used as the argument to the --prefix configuration switch.)

$ export RISCV=$TOP/riscv

If your $PATH variable does not contain the directory specified by $RISCV, add it to the $PATH environment variable now:

$ export PATH=$PATH:$RISCV/bin

Since we only need to build a few tools, we will use a modified build script, listed in its entirety below. Remember that we'll build riscv64-unknown-linux-gnu-gcc shortly afterwards. If you want to build the full toolchain for later use, see here.

[build-spike-only.sh contents]
1 #!/bin/bash
2 . build.common
3 build_project riscv-fesvr --prefix=$RISCV
4 build_project riscv-isa-sim --prefix=$RISCV --with-fesvr=$RISCV

Run the build script.

$ ./build-spike-only.sh

Building riscv64-unknown-linux-gnu-gcc (11.41 SBU)

riscv64-unknown-linux-gnu-gcc is the name of the cross-compiler used to build binaries linked to the GNU C Library (glibc) instead of the Newlib library. You can build Linux with riscv64-unknown-elf-gcc, but you will need riscv64-unknown-linux-gnu-gcc to cross-compile applications, so we will build that instead.

Enter the riscv-gnu-toolchain directory and run the configure script to generate the Makefile.

$ ./configure --prefix=$RISCV

These instructions will place your riscv64-unknown-linux-gnu-gcc tools in the same installation directory as the riscv64-unknown-elf-gcc tool installed earlier. This arrangement is the simplest, but you could optionally supply a different prefix, so long as the bin directory within that prefix is in your PATH.

Run this command to start the build process:

$ make linux

Building the Linux Kernel (0.40 + ε SBU)

Obtaining and Patching the Kernel Sources

We are finally poised to bring in the Linux kernel sources. Change out of the riscv-tools/riscv-gnu-toolchain directory and clone the riscv-linux Git repository into this directory: linux-3.14._xx_, where xx represents the current minor revision (which, as of 11 February 2014, is "33").

$ cd $TOP
$ git clone https://github.com/riscv/riscv-linux.git linux-3.14.33

Download the current minor revision of the 3.14 Linux kernel series from The Linux Kernel Archives, and in one fell swoop, untar them over our repository. (The -k switch ensures that our .gitignore and README files don't get clobbered.)

$ curl -L https://www.kernel.org/pub/linux/kernel/v3.x/linux-3.14.33.tar.xz | tar -xJkf -

Configuring the Linux Kernel

The Linux kernel is seemingly infinitely configurable. However, with the current development status, there aren't that many devices or options to tweak. However, start with a default configuration that should work out-of-the-box with the ISA simulator.

$ make ARCH=riscv defconfig

If you want to edit the configuration, you can use a text-based GUI (ncurses) to edit the configuration:

O$ make ARCH=riscv menuconfig

Among other things, we have enabled by default procfs, ext2, and the HTIF virtualized devices (a block driver and console). In development, it can be very useful to enable "early printk", which will print messages to the console if the kernel crashes very early. You can access this option at "Early printk" in the "Kernel hacking" submenu.

Linux kernel menuconfig interface.

Begin building the kernel once you're satisfied with your configuration. Note the pattern: to build the RISC-V kernel, you must specify the ARCH=riscv in each invocation of make. This line is no exception. If you want to speed up the process, you can pass the -j [number] option to make.

$ make -j16 ARCH=riscv

Congratulations! You've just cross-compiled the Linux kernel for RISC-V! However, there are a few more things to take care of before we boot it.

Building BusyBox (0.26 SBU)

We currently develop with BusyBox, an unbelievably useful set of utilities that all compile into one multi-use binary. We use BusyBox without source code modifications. You can obtain the source at https://www.busybox.net. In our case, we will use BusyBox 1.26.2, but other versions should work fine.

Currently, we need it for its init and ash applets, but with bash cross-compiled for RISC-V, there is no longer a need for ash.

First, obtain and untar the source:

$ curl -L http://busybox.net/downloads/busybox-1.26.2.tar.bz2 > busybox-1.26.2.tar.bz2
$ tar xvjf busybox-1.26.2.tar.bz2

Then, enter the directory and turn off every configuration option:

$ cd busybox-1.26.2
$ make allnoconfig

We will need to change the cross-compiler, set the build to "static" (if desired, you can make it dynamic, but you'll have to copy some libraries later). We will also enable the init, ash, and mount applets. Also, disable job control for ash when the drop down menu for ash's suboptions appear.

Here are the configurations you will have to change:

• CONFIG_STATIC=y, listed as "Build BusyBox as a static binary (no shared libs)" in BusyBox Settings → Build Options
• CONFIG_CROSS_COMPILER_PREFIX=riscv64-unknown-linux-gnu-, listed as "Cross Compiler prefix" in BusyBox Settings → Build Options
• CONFIG_FEATURE_INSTALLER=y, listed as "Support --install [-s] to install applet links at runtime" in BusyBox Settings → General Configuration
• CONFIG_INIT=y, listed as "init" in Init utilities
• CONFIG_ASH=y, listed as "ash" in Shells
• CONFIG_ASH_JOB_CONTROL=n, listed as "Ash → Job control" in Shells
• CONFIG_MOUNT=y, listed as "mount" in Linux System Utilities

Enter the configuration interface much in the same way as that of the Linux kernel:

O$ make menuconfig

BusyBox menuconfig interface. Looks familiar, eh?

Once you've finished, make BusyBox. You don't need to specify $ARCH, because we've passed the name of the cross-compiler prefix.

$ make -j16

Once that completes, you now have a BusyBox binary cross-compiled to run on RISC-V. Now we'll need a way for the kernel to access the binary, and we'll use a root disk image for that. Before we proceed, change back into the directory with the Linux sources.

$ cd $TOP/linux-3.14.33

Creating a Root Disk Image

We use an initramfs to store our binaries (BusyBox in particular).

Currently, we have a root file system pre-packaged specifically for the RISC-V release. You can obtain it by heading to the index of my website, https://ocf.berkeley.edu/~qmn, finding my email, and contacting me.

To create your own initramfs, there are a few directories that you should have:

• /bin
• /dev
• /etc
• /lib
• /proc
• /sbin
• /tmp
• /usr

So create them:

$ mkdir root
$ cd root
$ mkdir -p bin etc dev lib proc sbin sys tmp usr usr/bin usr/lib usr/sbin

Then, place the BusyBox executable we just compiled in /bin.

$ cp $TOP/busybox-1.26.2/busybox bin

If you have built BusyBox statically, that will be all that's needed. If you want to build BusyBox dynamically, you will need to follow a slightly different procedure, described here.

We will also need to prepare an initialization table in the aptly-named file inittab, placed in /etc. Here is the inittab from our disk image:

::sysinit:/bin/busybox mount -t proc proc /proc
::sysinit:/bin/busybox mount -t tmpfs tmpfs /tmp
::sysinit:/bin/busybox mount -o remount,rw /dev/htifblk0 /
::sysinit:/bin/busybox --install -s
/dev/console::sysinit:-/bin/ash

Line 1 mounts the procfs filesystem onto /proc. Line 2 does similarly for tmpfs. Line 3 mounts the HTIF-virtualized block device (htifbd) onto root. Line 4 installs the various BusyBox applet symbolic links in /bin and elsewhere to make it more convenient to run them. Finally, line 5 opens up an ash shell on the HTIF-virtualized TTY (console, mapped to ttyHTIF) for a connection.

Download a copy of the example inittab using this command:

$ curl -L http://riscv.org/install-guides/linux-inittab > etc/inittab

If you would like to use getty instead, change line 5 to invoke that:

5 ::respawn:/bin/busybox getty 38400 ttyHTIF0

Once you've booted Linux and created the symlinks with line 4, they will persist between boots of the Linux kernel. This will cause a bunch of unsightly errors in every subsequent boot of the kernel. At the next boot, comment out line 4.

Also, we will need to create a symbolic link to /bin/busybox for init to work.

$ ln -s ../bin/busybox sbin/init
$ ln -s sbin/init init

We'll also need a character device for the console:

sudo mknod dev/console c 5 1

We are ready to create our initramfs:

find . | cpio --quiet -o -H newc > <riscv-linux>/rootfs.cpio

Configure linux to embed the created cpio archive. In the riscv-linux folder type

make ARCH=riscv menuconfig

Enter to General Setup, mark "Initial RAM filesystem and RAM disk". Then go to the option "Initramfs source file" and press enter to change it to "rootfs.cpio". Then Exit all the way back and save to .config.

Don't forget to rebuild riscv-linux and riscv-pk!

cd <riscv-linux>
make -j4 ARCH=riscv vmlinux
cd <riscv-pk>/build
rm -rf *
../configure --prefix=$RISCV --host=riscv64-unknown-linux-gnu --with-payload=<riscv-linux>/vmlinux
make
make install

Now, we're ready to boot a most basic kernel, with a shell. Invoke spike, the RISC-V architectural simulator, named after the golden spike that joined the two tracks of the Transcontinental Railroad, and considered to be the golden model of execution. The command looks like this:

$ spike bbl vmlinux

vmlinux is the name of the compiled Linux kernel binary.

If there are no problems, an ash prompt will appear after the boot process completes. It will be pretty useless without the usual plethora of command-line utilities, but you can add them as BusyBox applets. Have fun!

To exit the simulator, hit Ctrl-C.

Linux boot and "Hello world!"

If you want to reuse your disk image in a subsequent boot of the kernel, remember to remove (or comment out) the line that creates the symbolic links to BusyBox applets. Otherwise, it will generate several (harmless) warnings in each subsequent boot.

"Help! It doesn't work!"

First take a look at the Newlib problem list which are also relevant to here. Here are some more problems that can occur in the linux build:

Problems with "flock"

Some filesystems don't support flock, e.g. nfs (you can check your filesystem by df -Th). Look for "+flock $(SYSROOT)/.lock" in the following files and delete them:

riscv-tools/riscv-gnu-toolchain/Makefile
riscv-tools/riscv-gnu-toolchain/Makefile.in
riscv-tools/riscv-gnu-toolchain/build/Makefile

Avoid building with concurrency (i.e. avoid running make with the -j flag).

"These critical programs are missing or too old: make"

Not sure why, but gmake doesn't work well for the riscv-tools build in some platforms. In order to use make instead of gmake, open the file <riscv-tools>/riscv-gnu-toolchain/riscv-glibc/configure and replace the following line:

for ac_prog in gnumake gmake make

with:

for ac_prog in gnumake make gmake

"Operation not permitted" when trying to create character device

This may occur when running the following command:

sudo mknod dev/console c 5 1

Even if you have sudo permissions, you may still see this message in some filesystem (e.g. nfs). You can create a virtual drive by:

dd if=/dev/zero of=root.bin bs=1M count=64
mkfs.ext2 -F root.bin
chmod 777 root.bin
mkdir mnt
sudo mount -o loop root.bin mnt

If the mkfs.ext2 command not found, try instead:

/sbin/mkfs.ext2 -F root.bin

Copy the contents in the above created root directory into the new mnt directory and continue to create the cpio archive with the mnt directory instead of the root directory.

When finished, you may unmount by:

cd ..
sudo umount root.bin

compiler-gcc6.h not found

Use newer linux version for RISC-V. You can find it in https://github.com/riscv/riscv-linux Notice that similar problems as detailed here may occur, so don't forget to check this problem list in case of problems.

Error on build about "mcmodel=medany"

Such error may occur in one of the stages that requires the RISC-V gcc compiler. Some build stages use the default x86 gcc compiler installed on the x86 machine to compile if the RISC-V gcc not found. Some possible cases for that:

• RISC-V compiler is not built.
• $RISCV/bin is not in $PATH (Use "setenv PATH $RISCV/bin" or similar export command to add it to path).
• RISC-V compiler has been built but for the wrong variant (built for newlib and not for linux, 32/64 bit variant issue...).
• gcc path is wrong. For example, if "CONFIG_CROSS_COMPILER_PREFIX=riscv-linux-" is used in the Busybox build configuration instead of "CONFIG_CROSS_COMPILER_PREFIX=riscv64-unknown-linux-gnu-" but the RISC-V compiler is built into riscv64-unknown-linux-gnu-gcc, the busybox configurator will not find the correct gcc and will use the x86 as default. Similar problem may occur when compiling https://github.com/riscv/riscv-pk with a wrong --host argument.

Spike exits immediately with "This is bbl's dummy_payload" message

https://github.com/riscv/riscv-pk should be rebuilt with --with-payload flag points to the compiled vmlinux (replace the riscv-pk and riscv-linux below with the appropriate repository paths):

cd <riscv-pk>/build
rm -rf *
../configure --prefix=$RISCV --host=riscv64-unknown-linux-gnu --with-payload=<riscv-linux>/vmlinux
make
make install

Optional Commands

Depending on your system, you may have to execute a few more shell commands or execute them differently. It's not too useful if you've arrived here after reading the main text of the document; it's best that you're referred here instead.

Building the Full Toolchain (7.62 SBU)

If you want to build riscv64-unknown-elf-gcc (as distinct from riscv64-unknown-linux-gnu-gcc), riscv-pk, and riscv-tests, then simply run the full build script rather than the abbreviated one I provided.

O$ ./build.sh

Return to text.

Installing a Fresh Copy of the Linux Headers

If you (or someone you know) has changed the Linux headers, you'll need to install a new version to your system root before you build riscv64-unknown-linux-gnu-gcc to make sure the kernel and the C library agree on their interfaces. (Note that you'll need to pull in the Linux kernel sources before you perform these steps. If you haven't, do so now.)

First, go to the Linux directory and perform a headers check:

O$ cd $TOP/linux-3.14.33
$ make ARCH=riscv headers_check

Once the headers have been checked, install them.

O$ make ARCH=riscv headers_install INSTALL_HDR_PATH=$RISCV/sysroot64/usr

(Substitute the path specified by INSTALL_HDR_PATH if so desired.)

Return to text.

Using Filesystem in Userspace (FUSE) to Create a Disk Image

If you are unable (or unwilling) to use mount to mount the newly-created disk image for modification, and you also have Filesystem in Userspace (FUSE), you can use these commands to modify your disk image.

First, create a folder as your mount point.

O$ mkdir mnt

Then, mount the disk image with FUSE. The -o +rw option is considered experimental by FUSE developers, and may corrupt your disk image. If you experience strange behaviors in your disk image, you might want to delete your image and make a new one. Continuing, mount the disk:

O$ fuseext2 -o rw+ root.bin mnt

Modify the disk image as described, but remember to unmount the disk using FUSE, not umount:

O$ fusermount -u mnt

Return to text.

Building BusyBox as a Dynamically-Linked Executable

If you want to conserve space on your root disk, or you want to support dynamically-linked binaries, you will want to build BusyBox as a dynamically-linked executable. You'll need to have these libraries:

• libc.so.6, the C library
• ld.so.1, the run-time dynamic linker

If BusyBox calls for additional libraries (e.g. libm), you will need to include those as well.

These were built when we compiled riscv64-unknown-linux-gnu-gcc and were placed in $RISCV/sysroot64. So, mount your root disk (if not mounted already), cd into it, and copy the libraries into lib:

O$ cp $RISCV/sysroot64/lib/libc.so.6 lib/
O$ cp $RISCV/sysroot64/lib/ld.so.1 lib/

That's it for the libraries. Go back to the BusyBox configuration and set BusyBox to be built as a dynamically-linked binary by unchecking the CONFIG_STATIC box in the menuconfig interface.

• CONFIG_STATIC=n, listed as "Build BusyBox as a static binary (no shared libs)" in BusyBox Settings → Build Options

To make things a little faster, I've used a bit of sed magic instead.

O$ cd $TOP/busybox-1.26.2
O$ sed -i 's/CONFIG_STATIC=y/# CONFIG_STATIC is not set/' .config

Then, rebuild and reinstall BusyBox into mnt/bin.

O$ make -j16
O$ cd $TOP/linux-3.14.33/mnt
O$ cp $TOP/busybox-1.26.2/busybox bin

Return to text.

References

• Waterman, A., Lee, Y., Patterson, D., and Asanovic, K,. "The RISC-V Instruction Set Manual," vol. II, https://inst.eecs.berkeley.edu/~cs152/sp12/handouts/riscv-supervisor.pdf, 2012.

• Bovet, D.P., and Cesati, M. Understanding the Linux Kernel, 3rd ed., O'Reilly, 2006.

• Gorman, M. Understanding the Linux Virtual Memory Manager, http://www.csn.ul.ie/~mel/docs/vm/guide/pdf/understand.pdf, 2003.

• Corbet, J., Rubini, A., and Kroah-Hartman, G. Linux Device Drivers, 3rd ed., O'Reilly, 2005.

• Beekmans, G. Linux From Scratch, version 7.3, http://www.linuxfromscratch.org/lfs/view/stable/, 2013.