RISC-V Meaty Skeleton with QEMU virt board: Difference between revisions

This tutorial assumes you have completed [[RISC-V_Bare_Bones|RISC-V Bare Bones]] on the QEMU <code>virt</code> board, or alternatively, [[HiFive-1_Bare_Bones|HiFive-1 Bare Bones]]. If not, you should complete them first for an overview of how to boot your own operating system on RISC-V. This tutorial is deliberately brief on concepts that have already been covered in the bare bones tutorials and their transitive prerequisites.

 

Fetch the latest version of GDB through [https://ftp.gnu.org/gnu/gdb/ https://ftp.gnu.org/gnu/gdb/]. The latest version at the time of writing is 12.1:

 

export GDB_VERSION="12.1"

wget https://ftp.gnu.org/gnu/gdb/gdb-${GDB_VERSION}.tar.xz

 

Unpack the archive:

 

tar xvf gdb-${GDB_VERSION}.tar.xz

 

Now move into the source directory:

 

pushd gdb-${GDB_VERSION}/

 

Create a build directory and move into it:

 

mkdir build

pushd build/

 

Now export a few variables as with building a cross-GCC or cross-binutils:

 

export PREFIX="$HOME/opt/cross"

export TARGET=riscv64-elf

export PATH="$PREFIX/bin:$PATH"

 

Configuration options are mostly the same as with building cross-GCC or cross-binutils. In particular, you may wish to enable the following features:

* <code>--with-expat</code>: Build with Expat, a library for XML parsing. Requires development headers for Expat to be installed on the build host

 

../configure --target=$TARGET \

--prefix="$PREFIX" \

--enable-tui=yes \

--with-expat

 

Now build the source code (this can take a while):

 

make -j$(nproc)

 

And install:

 

make -C gdb install

 

If you wish to keep the source tree available for conveniently re-building GDB in the future (e.g. with a different set of options), clean up the build files now:

 

make clean

 

Move one level up to the project root:

 

popd

 

Remove the <code>build/</code> directory we created:

 

rm -rf build/

 

Move up one more level:

 

popd

 

Double check our cross-debugger is properly installed:

 

which -- $TARGET-gdb || echo $TARGET-gdb is not in the PATH

 

Now you may safely remove the source tree and archive, if you wish:

 

rm -rf gdb-${GDB_VERSION}/

rm gdb-${GDB_VERSION}.tar.xz

 

If <code>$PREFIX/bin</code> is not in your path already, you may wish to persist it by writing it to your profile:

 

echo "export PATH=\"\$HOME/opt/cross/bin:\$PATH\"" >> $HOME/.profile

source $HOME/.profile

 

==Dependencies==

Fetch the source code from the <code>v0.0.1</code> release of [https://github.com/DonaldKellett/marvelos https://github.com/DonaldKellett/marvelos] code-named "Meaty Skeleton", using [https://git-scm.com/ Git]:

 

git clone --branch v0.0.1 https://github.com/DonaldKellett/marvelos.git

 

Operating systems development is about being an expert. Take the time to read the code carefully through and understand it. Please seek further information and help if you don't understand aspects of it. This code is minimal and almost everything is done deliberately, often to pre-emptively solve future problems.

Run <code>make $TARGET</code> with <code>TARGET</code> set to your desired target to execute the specified target. For example, to build the kernel image and run it in QEMU:

 

make run

 

Additionally, the default target is <code>all</code> if not specified:

 

make

 

# Build

CC=riscv64-elf-gcc

rm -vf *.o

rm -vf $(KERNEL_IMAGE)

 

===Kernel source===

====src/common/common.h====

 

#ifndef COMMON_H

#define COMMON_H

 

#endif

 

====src/common/common.c====

 

#include <stdarg.h>

#include "common.h"

asm volatile ("wfi");

}

 

====src/syscon/syscon.h====

 

#ifndef SYSCON_H

#define SYSCON_H

 

#endif

 

====src/syscon/syscon.c====

 

#include <stdint.h>

#include "syscon.h"

*(uint32_t *)SYSCON_ADDR = 0x7777;

}

 

====src/uart/uart.h====

 

#ifndef UART_H

#define UART_H

 

#endif

 

====src/uart/uart.c====

 

#include <stddef.h>

#include <stdint.h>

va_end(arg);

}

 

====src/kmain.c====

 

#include "uart/uart.h"

#include "syscon/syscon.h"

poweroff();

}

 

==Running the project==

* [[HiFive-1_Bare_Bones|HiFive-1 Bare Bones]]

* [[Meaty_Skeleton|Meaty Skeleton]]