1 RISC-V Open Source Supervisor Binary Interface (OpenSBI)
2 ========================================================
7 The OpenSBI project is copyright (c) 2019 Western Digital Corporation
8 or its affiliates and other contributors.
10 It is distributed under the terms of the BSD 2-clause license
11 ("Simplified BSD License" or "FreeBSD License", SPDX: *BSD-2-Clause*).
12 A copy of this license with OpenSBI copyright can be found in the file
15 All source files in OpenSBI contain the 2-Clause BSD license SPDX short
16 identifier in place of the full license text.
19 SPDX-License-Identifier: BSD-2-Clause
22 This enables machine processing of license information based on the SPDX
23 License Identifiers that are available on the [SPDX] web site.
25 OpenSBI source code also contains code reused from other projects as listed
26 below. The original license text of these projects is included in the source
27 files where the reused code is present.
29 * The libfdt source code is disjunctively dual licensed
30 (GPL-2.0+ OR BSD-2-Clause). Some of this project code is used in OpenSBI
31 under the terms of the BSD 2-Clause license. Any contributions to this
32 code must be made under the terms of both licenses.
34 See also the [third party notices] file for more information.
39 The **RISC-V Supervisor Binary Interface (SBI)** is the recommended interface
42 1. A platform-specific firmware running in M-mode and a bootloader, a
43 hypervisor or a general-purpose OS executing in S-mode or HS-mode.
44 2. A hypervisor running in HS-mode and a bootloader or a general-purpose OS
47 The *RISC-V SBI specification* is maintained as an independent project by the
48 RISC-V Foundation on [Github].
50 The goal of the OpenSBI project is to provide an open-source reference
51 implementation of the RISC-V SBI specifications for platform-specific firmwares
52 executing in M-mode (case 1 mentioned above). An OpenSBI implementation can be
53 easily extended by RISC-V platform and system-on-chip vendors to fit a
54 particular hardware configuration.
56 The main component of OpenSBI is provided in the form of a platform-independent
57 static library **libsbi.a** implementing the SBI interface. A firmware or
58 bootloader implementation can link against this library to ensure conformance
59 with the SBI interface specifications. *libsbi.a* also defines an interface for
60 integrating with platform-specific operations provided by the platform firmware
61 implementation (e.g. console access functions, inter-processor interrupt
64 To illustrate the use of the *libsbi.a* library, OpenSBI also provides a set of
65 platform-specific support examples. For each example, a platform-specific
66 static library *libplatsbi.a* can be compiled. This library implements
67 SBI call processing by integrating *libsbi.a* with the necessary
68 platform-dependent hardware manipulation functions. For all supported platforms,
69 OpenSBI also provides several runtime firmware examples built using the platform
70 *libplatsbi.a*. These example firmwares can be used to replace the legacy
71 *riscv-pk* bootloader (aka BBL) and enable the use of well-known bootloaders
76 Currently, OpenSBI fully supports SBI specification *v0.2*. OpenSBI also
77 supports Hart State Management (HSM) SBI extension starting from OpenSBI v0.7.
78 HSM extension allows S-mode software to boot all the harts a defined order
79 rather than legacy method of random booting of harts. As a result, many
80 required features such as CPU hotplug, kexec/kdump can also be supported easily
81 in S-mode. HSM extension in OpenSBI is implemented in a non-backward compatible
82 manner to reduce the maintenance burden and avoid confusion. That's why, any
83 S-mode software using OpenSBI will not be able to boot more than 1 hart if HSM
84 extension is not supported in S-mode.
86 Linux kernel already supports SBI v0.2 and HSM SBI extension starting from
87 **v5.7-rc1**. If you are using an Linux kernel older than **5.7-rc1** or any
88 other S-mode software without HSM SBI extension, you should stick to OpenSBI
89 v0.6 to boot all the harts. For a UMP systems, it doesn't matter.
91 N.B. Any S-mode boot loader (i.e. U-Boot) doesn't need to support HSM extension,
92 as it doesn't need to boot all the harts. The operating system should be
93 capable enough to bring up all other non-booting harts using HSM extension.
98 OpenSBI can be compiled natively or cross-compiled on a x86 host. For
99 cross-compilation, you can build your own toolchain, download a prebuilt one
100 from the [Bootlin toolchain repository] or install a distribution-provided
101 toolchain; if you opt to use LLVM/Clang, most distribution toolchains will
102 support cross-compiling for RISC-V using the same toolchain as your native
103 LLVM/Clang toolchain due to LLVM's ability to support multiple backends in the
104 same binary, so is often an easy way to obtain a working cross-compilation
107 Please note that only a 64-bit version of the toolchain is available in
108 the Bootlin toolchain repository for now.
110 Building and Installing the OpenSBI Platform-Independent Library
111 ----------------------------------------------------------------
113 The OpenSBI platform-independent static library *libsbi.a* can be compiled
114 natively or it can be cross-compiled on a host with a different base
115 architecture than RISC-V.
117 For cross-compiling, the environment variable *CROSS_COMPILE* must be defined
118 to specify the name prefix of the RISC-V compiler toolchain executables, e.g.
119 *riscv64-unknown-elf-* if the gcc executable used is *riscv64-unknown-elf-gcc*.
121 To build *libsbi.a* simply execute:
126 All compiled binaries as well as the resulting *libsbi.a* static library file
127 will be placed in the *build/lib* directory. To specify an alternate build root
130 make O=<build_directory>
133 To generate files to be installed for using *libsbi.a* in other projects, run:
138 This will create the *install* directory with all necessary include files
139 copied under the *install/include* directory and the library file copied into
140 the *install/lib* directory. To specify an alternate installation root
143 make I=<install_directory> install
146 Building and Installing a Reference Platform Static Library and Firmware
147 ------------------------------------------------------------------------
149 When the *PLATFORM=<platform_subdir>* argument is specified on the make command
150 line, the platform-specific static library *libplatsbi.a* and firmware examples
151 are built for the platform *<platform_subdir>* present in the directory
152 *platform* in the OpenSBI top directory. For example, to compile the platform
153 library and the firmware examples for the QEMU RISC-V *virt* machine,
154 *<platform_subdir>* should be *generic*.
156 To build *libsbi.a*, *libplatsbi.a* and the firmware for one of the supported
159 make PLATFORM=<platform_subdir>
162 An alternate build directory path can also be specified:
164 make PLATFORM=<platform_subdir> O=<build_directory>
167 The platform-specific library *libplatsbi.a* will be generated in the
168 *build/platform/<platform_subdir>/lib* directory. The platform firmware files
169 will be under the *build/platform/<platform_subdir>/firmware* directory.
170 The compiled firmwares will be available in two different formats: an ELF file
171 and an expanded image file.
173 To install *libsbi.a*, *libplatsbi.a*, and the compiled firmwares, run:
175 make PLATFORM=<platform_subdir> install
178 This will copy the compiled platform-specific libraries and firmware files
179 under the *install/platform/<platform_subdir>/* directory. An alternate
180 install root directory path can be specified as follows:
182 make PLATFORM=<platform_subdir> I=<install_directory> install
185 In addition, platform-specific configuration options can be specified with the
186 top-level make command line. These options, such as *PLATFORM_<xyz>* or
187 *FW_<abc>*, are platform-specific and described in more details in the
188 *docs/platform/<platform_name>.md* files and
189 *docs/firmware/<firmware_name>.md* files.
191 Building 32-bit / 64-bit OpenSBI Images
192 ---------------------------------------
193 By default, building OpenSBI generates 32-bit or 64-bit images based on the
194 supplied RISC-V cross-compile toolchain. For example if *CROSS_COMPILE* is set
195 to *riscv64-unknown-elf-*, 64-bit OpenSBI images will be generated. If building
196 32-bit OpenSBI images, *CROSS_COMPILE* should be set to a toolchain that is
197 pre-configured to generate 32-bit RISC-V codes, like *riscv32-unknown-elf-*.
199 However it's possible to explicitly specify the image bits we want to build with
200 a given RISC-V toolchain. This can be done by setting the environment variable
201 *PLATFORM_RISCV_XLEN* to the desired width, for example:
204 export CROSS_COMPILE=riscv64-unknown-elf-
205 export PLATFORM_RISCV_XLEN=32
208 will generate 32-bit OpenSBI images. And vice vesa.
210 Building with Clang/LLVM
211 ------------------------
213 OpenSBI can also be built with Clang/LLVM. To build with just Clang but keep
214 the default binutils (which will still use the *CROSS_COMPILE* prefix if
215 defined), override the *CC* make variable with:
220 To build with a full LLVM-based toolchain, not just Clang, enable the *LLVM*
226 When using Clang, *CROSS_COMPILE* often does not need to be defined unless
227 using GNU binutils with prefixed binary names. *PLATFORM_RISCV_XLEN* will be
228 used to infer a default triple to pass to Clang, so if *PLATFORM_RISCV_XLEN*
229 itself defaults to an undesired value then prefer setting that rather than the
230 full triple via *CROSS_COMPILE*. If *CROSS_COMPILE* is nonetheless defined,
231 rather than being used as a prefix for the executable name, it will instead be
232 passed via the `--target` option with the trailing `-` removed, so must be a
235 These can also be mixed; for example using a GCC cross-compiler but LLVM
238 make CC=riscv64-unknown-elf-gcc LLVM=1
241 These variables must be passed for all the make invocations described in this
244 NOTE: Using Clang with a `riscv*-linux-gnu` GNU binutils linker has been seen
245 to produce broken binaries with missing relocations; it is therefore currently
246 recommended that this combination be avoided or *FW_PIC=n* be used to disable
247 building OpenSBI as a position-independent binary.
249 Contributing to OpenSBI
250 -----------------------
252 The OpenSBI project encourages and welcomes contributions. Contributions should
253 follow the rules described in the OpenSBI [Contribution Guideline] document.
254 In particular, all patches sent should contain a Signed-off-by tag.
256 The [Contributors List] document provides a list of individuals and
257 organizations actively contributing to the OpenSBI project.
262 Detailed documentation of various aspects of OpenSBI can be found under the
263 *docs* directory. The documentation covers the following topics.
265 * [Contribution Guideline]: Guideline for contributing code to OpenSBI project
266 * [Library Usage]: API documentation of OpenSBI static library *libsbi.a*
267 * [Platform Requirements]: Requirements for using OpenSBI on a platform
268 * [Platform Support Guide]: Guideline for implementing support for new platforms
269 * [Platform Documentation]: Documentation of the platforms currently supported.
270 * [Firmware Documentation]: Documentation for the different types of firmware
271 examples build supported by OpenSBI.
272 * [Domain Support]: Documentation for the OpenSBI domain support which helps
273 users achieve system-level partitioning using OpenSBI.
275 OpenSBI source code is also well documented. For source level documentation,
276 doxygen style is used. Please refer to the [Doxygen manual] for details on this
279 Doxygen can be installed on Linux distributions using *.deb* packages using
280 the following command.
282 sudo apt-get install doxygen doxygen-latex doxygen-doc doxygen-gui graphviz
285 For *.rpm* based Linux distributions, the following commands can be used.
287 sudo yum install doxygen doxygen-latex doxywizard graphviz
291 sudo yum install doxygen doxygen-latex doxywizard graphviz
294 To build a consolidated *refman.pdf* of all documentation, run:
300 make O=<build_directory> docs
303 the resulting *refman.pdf* will be available under the directory
304 *<build_directory>/docs/latex*. To install this file, run:
310 make I=<install_directory> install_docs
313 *refman.pdf* will be installed under *<install_directory>/docs*.
315 [Github]: https://github.com/riscv/riscv-sbi-doc
316 [U-Boot]: https://www.denx.de/wiki/U-Boot/SourceCode
317 [Bootlin toolchain repository]: https://toolchains.bootlin.com/
318 [COPYING.BSD]: COPYING.BSD
319 [SPDX]: http://spdx.org/licenses/
320 [Contribution Guideline]: docs/contributing.md
321 [Contributors List]: CONTRIBUTORS.md
322 [Library Usage]: docs/library_usage.md
323 [Platform Requirements]: docs/platform_requirements.md
324 [Platform Support Guide]: docs/platform_guide.md
325 [Platform Documentation]: docs/platform/platform.md
326 [Firmware Documentation]: docs/firmware/fw.md
327 [Domain Support]: docs/domain_support.md
328 [Doxygen manual]: http://www.doxygen.nl/manual/index.html
329 [Kendryte standalone SDK]: https://github.com/kendryte/kendryte-standalone-sdk
330 [third party notices]: ThirdPartyNotices.md