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This is Edition 0.0. \newline
Copyright (C) 2024 Adrien 'neox' Bourmault \href{mailto:neox@gnu.org}{<neox@gnu.org>} \newline
Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.3
or any later version published by the Free Software Foundation;
with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts.
A copy of the license is included in the section entitled "GNU
Free Documentation License".
\newpage
% Table of contents
\tableofcontents
\newpage
\chapter*{Abstract}
\addcontentsline{toc}{chapter}{Abstract}
The global trend is towards the scarcity of free software-compatible hardware,
and soon there will be no computer that will work without software domination
by big companies, especially involving BIOSes. A Basic Input Output System
(BIOS) was originally a set of low-level functions contained in the read-only
memory of a computer's mainboard, enabling it to perform basic operations when
powered up. However, the definition of a BIOS has evolved to include what used
to be known as Power On Self Test (POST) for the presence of peripherals,
allocating resources for them to avoid conflicts, and then handing over to an
operating system boot loader. Nowadays, the bulk of the BIOS work is the
initialization and training of RAM. This means, for example, initializing the
memory controller and optimizing timing and read/write voltage for optimal
performance, making the code complex, as its role is to optimize several
parallel buses operating at high speeds and shared by many CPU cores, and make
them act as a homogeneous whole. \\
This documentation is the product of a project hosted by the \textit{LIP6 laboratory} and supported by the \textit{GNU Boot Project} and the \textit{Free Software Foundation}, delves into the importance of firmware in the hardware initialization of modern computers.
It explores various aspects of firmware, such as Intel Management
Engine (ME), AMD Platform Security Processor (PSP), Advanced Configuration and
Power Interface (ACPI), and System Management Mode (SMM). Additionally, it
provides an in-depth look at memory initialization and training algorithms,
highlighting their critical role in system stability and performance. \\
Examples of the implementation in the Asus KGPE-D16 mainboard are presented, describing its hardware characteristics, topology, and the crucial role of firmware in its operation after the mainboard architecture is examined.
Practical examples illustrate the impact of firmware on hardware
initialization, memory optimization, resource allocation, power management,
and security. Specific algorithms used for memory training and their outcomes
are analyzed to demonstrate the complexity and importance of firmware in
achieving optimal system performance. \\
Furthermore, the article explores the relationship between firmware and
hardware virtualization, discussing how modern firmware supports and enhances
virtualized environments. Security considerations and future trends in
firmware development are also addressed, emphasizing the need for continued
research and advocacy for free software-compatible hardware. The article
concludes with a call to action, urging the development of libre
firmware solutions to ensure greater control and security in computing.
\chapter{Introduction to firmware and BIOS evolution}
\section{Historical context of BIOS}
\subsection{Definition and origin}
The BIOS (Basic Input/Output System) is firmware used to perform hardware
initialization during the booting process and to provide runtime services
for operating systems and programs. Being a critical component for the
startup of personal computers, acting as an intermediary between the
computer's hardware and its operating system, the BIOS is embedded on a
chip on the motherboard and is the first code that runs when a PC is
powered on. The concept of BIOS has its roots in the early days of personal
computing. It was first developed by IBM for their IBM PC, which was
introduced in 1981. The term BIOS itself was coined by Gary Kildall, who
developed the CP/M (Control Program for Microcomputers) operating system.
In CP/M, BIOS was used to describe a component that interfaced directly
with the hardware, allowing the operating system to be somewhat
hardware-independent. \newline
IBM's implementation of BIOS became a de facto standard in the industry,
as it was part of the IBM PC's open architecture, which refers to the
design philosophy adopted by IBM when developing the IBM Personal Computer
(PC), introduced in 1981. This architecture is characterized by the use of
off-the-shelf components and publicly available specifications, which
allowed other manufacturers to create compatible hardware and software.
It was in fact a departure from the proprietary systems prevalent at
the time, where companies closely guarded their designs to maintain
control over the hardware and software ecosystem.
For example, IBM used the Intel 8088 CPU, a well-documented and widely
available processor, and also the Industry Standard Architecture (ISA) bus,
which defined how various components like memory, storage, and peripherals
communicated with the CPU. This open architecture allowed other
manufacturers to create IBM-compatible computers, also known as "clones",
which further popularized the BIOS concept. As a result, the IBM PC BIOS
set the stage for a standardized method of interacting with computer
hardware, which has evolved over the years but remains fundamentally the
same in principle. IBM also published detailed technical documentation at
that time, including circuit diagrams, BIOS listings, and interface
specifications. This transparency allowed other companies to understand and
replicate the IBM PC's functionality.
\subsection{Functionalities and limitations}
The Basic Input/Output System (BIOS) is a foundational firmware component
in early personal computers, responsible for initializing hardware and
booting the operating system. Developed as part of IBM's original PC
design, the BIOS provided essential functionalities. \newline
When a computer is powered on, the BIOS executes a Power-On Self-Test
(POST), a diagnostic sequence that verifies the integrity and functionality
of critical hardware components such as the CPU, RAM, disk drives,
keyboard, and other peripherals. This process ensures that all essential
hardware components are operational before the system attempts to load the
operating system. If any issues are detected, the BIOS generates error
messages or beep codes to alert the user.
Following the successful completion of POST, the BIOS runs the bootstrap
loader, a small program that identifies the operating system's bootloader
on a storage device, such as a hard drive, floppy disk, or optical drive.
The bootstrap loader then transfers control to the OS bootloader,
initiating the process of loading the operating system into the computer's
memory and starting it. This step effectively bridges the gap between
hardware initialization and operating system execution.
The BIOS also provides a set of low-level software routines known as
interrupts. These routines enable software to perform basic input/output
operations, such as reading from the keyboard, writing to the display, and
accessing disk drives, without needing to manage the hardware directly. By
providing standardized interfaces for hardware components, the BIOS
simplifies software development and improves compatibility across different
hardware configurations. \newline
Despite its essential role, the early BIOS had several limitations.
One significant limitation was its limited storage capacity.
Early BIOS firmware was stored in Read-Only Memory (ROM) chips with very
limited storage, often just a few kilobytes. This constrained the
complexity and functionality of the BIOS, limiting it to only the most
essential tasks needed to start the system and provide basic hardware
control. The original BIOS was also non-extensible. ROM chips were
typically soldered onto the motherboard, making updates difficult and
costly. Bug fixes, updates for new hardware support, or enhancements
required replacing the ROM chip, leading to challenges in maintaining and
upgrading systems. Furthermore, the early BIOS was tailored for the
specific hardware configurations of the initial IBM PC models, which
included a limited set of peripherals and expansion options. As new
hardware components and peripherals were developed, the BIOS often needed
to be updated to support them, which was not always feasible or timely.
Performance bottlenecks were another limitation. The BIOS provided basic
input/output operations that were often slower than direct hardware access
methods. For example, disk I/O operations through BIOS interrupts were
slower compared to later direct access methods provided by operating
systems, resulting in performance bottlenecks, especially for
disk-intensive operations. This inflexibility restricts the ability to
support new hardware and technologies efficiently.
Early BIOS implementations also had minimal security features. There were
no mechanisms to verify the integrity of the BIOS code or to protect
against unauthorized modifications, leaving systems vulnerable to attacks
that could alter the BIOS and potentially compromise the entire system,
such as rootkits and firmware viruses.
Added to that, the traditional BIOS operates in 16-bit real mode, a
constraint that limits the amount of code and memory it can address. This
limitation hinders the performance and complexity of firmware, making
it less suitable for modern computing needs \cite{intel_uefi}.
Additionally, BIOS relies on the Master Boot Record (MBR) partitioning
scheme, which supports a maximum disk size of 2 terabytes and allows only
four primary partitions \cite{uefi_spec}\cite{russinovich2012}.
This constraint has become a
significant drawback as storage capacities have increased.
Furthermore, the traditional BIOS has limited flexibility and is
challenging to update or extend. This inflexibility restricts the ability
to support new hardware and technologies efficiently
\cite{smith_2017}\cite{acmcs2015}.
\section{Modern BIOS and UEFI}
\subsection{Transition from traditional BIOS to UEFI (Unified Extensible Firmware Interface)}
All the limitations listed earlier have necessitated a transition to a more
modern firmware interface, designed to address the shortcomings of the
traditional BIOS. This section delves into the historical context of this
shift, the driving factors behind it, and the advantages UEFI offers over
the traditional BIOS.
The development of UEFI began in the mid-1990s as part of the Intel Boot
Initiative, which aimed to modernize the boot process and overcome the
limitations of the traditional BIOS. By 2005, the Unified EFI Forum, a
consortium of technology companies including Intel, AMD, and Microsoft,
had formalized the UEFI specification \cite{uefi_spec}. UEFI was designed
to address the shortcomings of the traditional BIOS, providing several key
improvements. \newline
One of the most significant advancements of UEFI is its support for 32-bit
and 64-bit modes, allowing it to address more memory and run more complex
firmware programs. This capability enables UEFI to handle the increased
demands of modern hardware and software \cite{intel_uefi}\cite{shin2011}.
Additionally, UEFI uses the GUID Partition Table (GPT) instead of the MBR,
supporting disks larger than 2 terabytes and allowing for a nearly
unlimited number of partitions
\cite{microsoft_uefi}\cite{russinovich2012}.
Improved boot performance is another driving factor. UEFI provides faster
boot times compared to the traditional BIOS, thanks to its efficient
hardware and software initialization processes. This improvement is
particularly beneficial for systems with complex hardware configurations,
where quick boot times are essential \cite{intel_uefi}.
UEFI's modular architecture makes it more extensible and easier to update
compared to the traditional BIOS. This design allows for the addition of
drivers, applications, and other components without requiring a complete
firmware overhaul, providing greater flexibility and adaptability to new
technologies \cite{smith_2017}\cite{acmcs2015}. UEFI also includes enhanced
security features such as \textit{Secure Boot}, which ensures that only
trusted software can be executed during the boot process, thereby
protecting the system from unauthorized modifications and malware
\cite{anderson_2018}\cite{chang2013}. \newline
The industry-wide support and standardization of UEFI have accelerated its
adoption across various platforms and devices. Major industry players,
including Intel, AMD, and Microsoft, have adopted UEFI as the new standard
for firmware interfaces, ensuring broad compatibility and interoperability
\cite{uefi_spec}.
\subsection{An other way with coreboot}
While UEFI has become the dominant firmware interface for modern computing
systems, it is not without its critics. Some of the primary concerns about
UEFI include its complexity, potential security vulnerabilities, and the
degree of control it provides to hardware manufacturers over the boot
process. As an alternative to UEFI, coreboot offers a different approach to
firmware that aims to address some of these concerns and continue the
evolution of BIOS.
\textit{coreboot}, originally known as LinuxBIOS, is a free firmware
project
initiated in 1999 by Ron Minnich and his team at the Los Alamos National
Laboratory. The project's primary goal was to create a fast, lightweight,
and flexible firmware solution that could initialize hardware and boot
operating systems quickly, while remaining transparent and
auditable\cite{coreboot}. \newline
One of the main advantages of \textit{coreboot} over UEFI is its
simplicity.
\textit{coreboot} is designed to perform only the minimal tasks required to
initialize hardware and pass control to a payload, such as a bootloader or
operating system kernel. This minimalist approach reduces the attack
surface and potential for security vulnerabilities, as there is less code
that could be exploited by malicious actors \cite{rudolph2007}.
Another significant benefit of \textit{coreboot} is its libre nature.
Unlike
UEFI, which is controlled by a consortium of hardware and software vendors,
\textit{coreboot}'s source code is freely available and can be audited,
modified,
and improved by anyone. This transparency ensures that security researchers
and developers can review the code for potential vulnerabilities and
contribute to its improvement, fostering a community-driven approach to
firmware development\cite{coreboot}.
\textit{coreboot} also supports a wide range of payloads, allowing users to
customize their boot process to suit their specific needs. Popular payloads
include SeaBIOS, which provides legacy BIOS compatibility, and Tianocore,
which offers UEFI functionality within the \textit{coreboot} framework.
This
flexibility allows \textit{coreboot} to be used in a variety of
environments, from
embedded systems to high-performance servers\cite{coreboot_payloads}.
\newline
Despite its advantages, \textit{coreboot} is not without its challenges.
The project
relies heavily on community contributions, and support for new hardware
often lags behind that of UEFI. Additionally, the minimalist design of
\textit{coreboot} means that some advanced features provided by UEFI, such
as Secure
Boot, are not available by default. However, the \textit{coreboot}
community
continues to work on adding new features and improving compatibility with
modern hardware\cite{coreboot_challenges}.
However, it's important to note that \textit{coreboot} is not entirely free
in all
aspects. Many modern processors and chipsets require proprietary binary
blobs for certain functionalities, such as memory initialization and
hardware management. These blobs are necessary for \textit{coreboot} to
function
correctly on a wide range of hardware, but they compromise the goal of
having a fully free firmware one day\cite{blobs}.
To address these concerns, the GNU Project has developed GNU Boot, a
fully free distribution of firmware, including \textit{coreboot}, that aims
to be
entirely free by avoiding the use of proprietary binary blobs. GNU Boot is
committed to using only free software for all aspects of firmware, making
it a preferred choice for users and organizations that prioritize software
freedom and transparency\cite{gnuboot}.
\section{Shift in firmware responsibilities}
Initially, we saw that the BIOS's primary function was to perform the
Power-On Self-Test (POST), a basic diagnostic testing process to check the
system's hardware components and ensure they were functioning correctly.
This included verifying the CPU, memory, and essential peripherals before
passing control to the operating system's bootloader. This process was
relatively simple, given the limited capabilities and straightforward
architecture of early computer systems\cite{smith_2017}. As computer
systems advanced, particularly with the advent of more sophisticated memory
technologies, the role of the BIOS expanded significantly. An example is
that modern memory modules operate at much higher speeds and capacities
than their predecessors, requiring precise configuration to ensure
stability and optimal performance.
We'll see in following sections how memory is taken care by firmware,
since the memory controller, a critical component in modern computer
systems, manages the data flow between the processor and memory modules.
Firmware then plays a crucial role in configuring this controller
during the boot process. This configuration includes setting memory
frequencies, voltage levels, and timing parameters to match the
specifications of the installed memory\cite{uefi_spec}.
The enhanced role of firmware in memory training and optimization directly
impacts system performance and stability. For example, overclocking
involves configuring the system to run at higher speeds than
manufacturer-specified limits. Firmware plays a key role in enabling
and managing overclocking, particularly for the memory subsystem. By
allowing adjustments to memory frequencies, voltages, and timings, it
provides tools for performance tuning while including safeguards to manage
the risks of instability and hardware damage \cite{anderson_2018}.
\chapter{Characteristics of Asus KGPE-D16 Mainboard}
\section{Overview of Asus KGPE-D16 Hardware}
\begin{itemize}
\item Description of the mainboard's hardware components
\begin{itemize}
\item CPU: Support for AMD Opteron 6000 series processors
\item RAM: 16 DDR3 DIMM slots supporting up to 256GB of memory
\item Expansion Slots: Multiple PCIe slots for expandability
\item Storage: SATA ports and potential for RAID configurations
\item Networking: Integrated dual gigabit Ethernet ports
\item Other Peripherals: USB ports, audio outputs, and additional I/O ports
\end{itemize}
\item Topology and Layout
\begin{itemize}
\item Physical layout of the mainboard
\item Placement of key components and their interactions
\item Cooling and power distribution
\end{itemize}
\end{itemize}
\section{Firmware's Role in Asus KGPE-D16}
\begin{itemize}
\item Initial hardware setup
\item Memory training and optimization
\item Resource allocation and conflict resolution
\item Power management and efficiency
\item Security features and updates
\end{itemize}
\chapter{Key Components in Modern Firmware}
\section{Advanced Configuration and Power Interface (ACPI)}
\begin{itemize}
\item Detailed explanation of ACPI
\item Role in power management and system configuration
\item Implementation in modern operating systems
\item \textbf{Asus KGPE-D16 Example}: ACPI utilization in power management and device configuration on the mainboard
\end{itemize}
\section{System Management Mode (SMM)}
\begin{itemize}
\item Definition and significance
\item How SMM enhances system security
\item Examples of SMM applications in real-world systems
\item \textbf{Asus KGPE-D16 Example}: SMM features and their impact on system security and functionality in the KGPE-D16
\end{itemize}
\section{AMD Platform Security Processor (PSP) and Intel Management Engine (ME)}
\begin{itemize}
\item Overview and purpose
\item Security implications, concerns and controversies
\item Interaction with system firmware
\item Differences between Intel ME and AMD PSP
\end{itemize}
\chapter{Memory Initialization and Training Algorithms}
\section{Importance of Memory Initialization}
\begin{itemize}
\item Steps involved in initializing the memory controller
\item Critical role in system stability and performance
\item \textbf{Asus KGPE-D16 Example}: Memory initialization process on the KGPE-D16 mainboard
\end{itemize}
Memory training involves several steps:
1. **Detection and Initialization**: The BIOS detects the installed memory
modules, determining their size, speed, and type.
2. **Configuration and Timing Setup**: The BIOS configures the memory
controller settings, including timings for memory access such as CAS
latency, RAS to CAS delay, and other parameters \cite{intel_uefi}.
3. **Training and Calibration**: The BIOS performs tests and adjustments to
calibrate the memory system, ensuring stable operation at optimal speeds by
adjusting signal voltages and testing data integrity \cite{wolf2006}.
These steps are crucial for modern systems, where improper memory
configuration can lead to instability, data corruption, or suboptimal
performance.
Memory timings, such as CAS latency, RAS to CAS delay, and others, must be
finely tuned to ensure optimal performance. The BIOS uses a combination of
predefined profiles and dynamic adjustments to achieve the best balance
between speed and stability. Advanced timing optimization involves setting
these parameters to ensure that memory operations are performed with
minimal latency and maximum throughput \cite{russinovich2012}.
\section{Memory Training Algorithms}
\begin{itemize}
\item Techniques used for training memory
\item Optimization of timings and voltage settings
\item Challenges in multi-core CPU environments
\item \textbf{Asus KGPE-D16 Example}: Specific algorithms used for memory training in the mainboard and their performance outcomes
\end{itemize}
To optimize memory performance, the BIOS employs various training
algorithms and calibration techniques. These methods test the memory under
different conditions and make necessary adjustments to improve stability
and efficiency. Key techniques include voltage adjustments, data integrity
testing, and signal timing calibration \cite{shin2011}.
Voltage adjustments involve tweaking the power supplied to the memory
modules to ensure reliable operation. Data integrity testing checks that
data can be accurately read and written, while signal timing calibration
fine-tunes the delays between different memory operations to minimize
latency.
\section{Practical Examples}
\begin{itemize}
\item Real-world scenarios where firmware played a crucial role in system performance
\item Analysis of firmware updates and their impact on the KGPE-D16 mainboard
\item User experiences and testimonials highlighting the importance of firmware
\item \textbf{Asus KGPE-D16 Example}: Specific case studies and firmware updates for the mainboard
\end{itemize}
\chapter{Firmware and Hardware Virtualization}
\section{Introduction to Hardware Virtualization}
\begin{itemize}
\item Definition and purpose of virtualization
\item How firmware interacts with virtualized environments
\item \textbf{Asus KGPE-D16 Example}: Virtualization capabilities and performance on the mainboard
\end{itemize}
\section{Role of BIOS/UEFI in Virtualization}
\begin{itemize}
\item Initialization and configuration for virtual machines
\item Resource allocation and management
\item \textbf{Asus KGPE-D16 Example}: BIOS/UEFI settings and their impact on virtualization efficiency on the KGPE-D16
\end{itemize}
\section{Security and freedom considerations}
\begin{itemize}
\item Security risks associated with virtualization
\item Measures taken by firmware to mitigate risks
\item \textbf{Asus KGPE-D16 Example}: Security measures implemented in the mainboard's firmware to support secure virtualization
\end{itemize}
\section{Future Trends in Firmware and Virtualization}
\begin{itemize}
\item Emerging advancements and their impact on firmware
\item Predictions for the evolution of BIOS/UEFI in virtualization
\item \textbf{Asus KGPE-D16 Example}: Potential future firmware updates and their expected impact on the mainboard's virtualization capabilities
\end{itemize}
\chapter*{Conclusion}
\addcontentsline{toc}{chapter}{Conclusion}
\section{Summary of Key Points}
\begin{itemize}
\item Recap of the evolution and current state of firmware
\item Importance of understanding modern BIOS functionalities
\item \textbf{Asus KGPE-D16 Example}: Summary of the mainboard's features and firmware contributions
\end{itemize}
\section{Call for Action}
\begin{itemize}
\item Advocacy for free software-compatible hardware
\item Encouraging research and development in libre firmware solutions
\end{itemize}
\newpage
% Bibliography
\nocite{*}
\addcontentsline{toc}{chapter}{Bibliography}
\printbibliography
\newpage
\chapter*{\rlap{GNU Free Documentation License}}
\addcontentsline{toc}{chapter}{GNU Free Documentation License}
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Document's license notice requires Cover Texts, you must enclose the
copies in covers that carry, clearly and legibly, all these Cover
Texts: Front-Cover Texts on the front cover, and Back-Cover Texts on
the back cover. Both covers must also clearly and legibly identify
you as the publisher of these copies. The front cover must present
the full title with all words of the title equally prominent and
visible. You may add other material on the covers in addition.
Copying with changes limited to the covers, as long as they preserve
the title of the Document and satisfy these conditions, can be treated
as verbatim copying in other respects.
If the required texts for either cover are too voluminous to fit
legibly, you should put the first ones listed (as many as fit
reasonably) on the actual cover, and continue the rest onto adjacent
pages.
If you publish or distribute Opaque copies of the Document numbering
more than 100, you must either include a machine-readable Transparent
copy along with each Opaque copy, or state in or with each Opaque copy
a computer-network location from which the general network-using
public has access to download using public-standard network protocols
a complete Transparent copy of the Document, free of added material.
If you use the latter option, you must take reasonably prudent steps,
when you begin distribution of Opaque copies in quantity, to ensure
that this Transparent copy will remain thus accessible at the stated
location until at least one year after the last time you distribute an
Opaque copy (directly or through your agents or retailers) of that
edition to the public.
It is requested, but not required, that you contact the authors of the
Document well before redistributing any large number of copies, to give
them a chance to provide you with an updated version of the Document.
\begin{center}
{\Large\bf 4. MODIFICATIONS\par}
\end{center}
You may copy and distribute a Modified Version of the Document under
the conditions of sections 2 and 3 above, provided that you release
the Modified Version under precisely this License, with the Modified
Version filling the role of the Document, thus licensing distribution
and modification of the Modified Version to whoever possesses a copy
of it. In addition, you must do these things in the Modified Version:
\begin{itemize}
\item[A.]
Use in the Title Page (and on the covers, if any) a title distinct
from that of the Document, and from those of previous versions
(which should, if there were any, be listed in the History section
of the Document). You may use the same title as a previous version
if the original publisher of that version gives permission.
\item[B.]
List on the Title Page, as authors, one or more persons or entities
responsible for authorship of the modifications in the Modified
Version, together with at least five of the principal authors of the
Document (all of its principal authors, if it has fewer than five),
unless they release you from this requirement.
\item[C.]
State on the Title page the name of the publisher of the
Modified Version, as the publisher.
\item[D.]
Preserve all the copyright notices of the Document.
\item[E.]
Add an appropriate copyright notice for your modifications
adjacent to the other copyright notices.
\item[F.]
Include, immediately after the copyright notices, a license notice
giving the public permission to use the Modified Version under the
terms of this License, in the form shown in the Addendum below.
\item[G.]
Preserve in that license notice the full lists of Invariant Sections
and required Cover Texts given in the Document's license notice.
\item[H.]
Include an unaltered copy of this License.
\item[I.]
Preserve the section Entitled ``History'', Preserve its Title, and add
to it an item stating at least the title, year, new authors, and
publisher of the Modified Version as given on the Title Page. If
there is no section Entitled ``History'' in the Document, create one
stating the title, year, authors, and publisher of the Document as
given on its Title Page, then add an item describing the Modified
Version as stated in the previous sentence.
\item[J.]
Preserve the network location, if any, given in the Document for
public access to a Transparent copy of the Document, and likewise
the network locations given in the Document for previous versions
it was based on. These may be placed in the ``History'' section.
You may omit a network location for a work that was published at
least four years before the Document itself, or if the original
publisher of the version it refers to gives permission.
\item[K.]
For any section Entitled ``Acknowledgements'' or ``Dedications'',
Preserve the Title of the section, and preserve in the section all
the substance and tone of each of the contributor acknowledgements
and/or dedications given therein.
\item[L.]
Preserve all the Invariant Sections of the Document,
unaltered in their text and in their titles. Section numbers
or the equivalent are not considered part of the section titles.
\item[M.]
Delete any section Entitled ``Endorsements''. Such a section
may not be included in the Modified Version.
\item[N.]
Do not retitle any existing section to be Entitled ``Endorsements''
or to conflict in title with any Invariant Section.
\item[O.]
Preserve any Warranty Disclaimers.
\end{itemize}
If the Modified Version includes new front-matter sections or
appendices that qualify as Secondary Sections and contain no material
copied from the Document, you may at your option designate some or all
of these sections as invariant. To do this, add their titles to the
list of Invariant Sections in the Modified Version's license notice.
These titles must be distinct from any other section titles.
You may add a section Entitled ``Endorsements'', provided it contains
nothing but endorsements of your Modified Version by various
parties---for example, statements of peer review or that the text has
been approved by an organization as the authoritative definition of a
standard.
You may add a passage of up to five words as a Front-Cover Text, and a
passage of up to 25 words as a Back-Cover Text, to the end of the list
of Cover Texts in the Modified Version. Only one passage of
Front-Cover Text and one of Back-Cover Text may be added by (or
through arrangements made by) any one entity. If the Document already
includes a cover text for the same cover, previously added by you or
by arrangement made by the same entity you are acting on behalf of,
you may not add another; but you may replace the old one, on explicit
permission from the previous publisher that added the old one.
The author(s) and publisher(s) of the Document do not by this License
give permission to use their names for publicity for or to assert or
imply endorsement of any Modified Version.
\begin{center}
{\Large\bf 5. COMBINING DOCUMENTS\par}
\end{center}
You may combine the Document with other documents released under this
License, under the terms defined in section~4 above for modified
versions, provided that you include in the combination all of the
Invariant Sections of all of the original documents, unmodified, and
list them all as Invariant Sections of your combined work in its
license notice, and that you preserve all their Warranty Disclaimers.
The combined work need only contain one copy of this License, and
multiple identical Invariant Sections may be replaced with a single
copy. If there are multiple Invariant Sections with the same name but
different contents, make the title of each such section unique by
adding at the end of it, in parentheses, the name of the original
author or publisher of that section if known, or else a unique number.
Make the same adjustment to the section titles in the list of
Invariant Sections in the license notice of the combined work.
In the combination, you must combine any sections Entitled ``History''
in the various original documents, forming one section Entitled
``History''; likewise combine any sections Entitled ``Acknowledgements'',
and any sections Entitled ``Dedications''. You must delete all sections
Entitled ``Endorsements''.
\begin{center}
{\Large\bf 6. COLLECTIONS OF DOCUMENTS\par}
\end{center}
You may make a collection consisting of the Document and other documents
released under this License, and replace the individual copies of this
License in the various documents with a single copy that is included in
the collection, provided that you follow the rules of this License for
verbatim copying of each of the documents in all other respects.
You may extract a single document from such a collection, and distribute
it individually under this License, provided you insert a copy of this
License into the extracted document, and follow this License in all
other respects regarding verbatim copying of that document.
\begin{center}
{\Large\bf 7. AGGREGATION WITH INDEPENDENT WORKS\par}
\end{center}
A compilation of the Document or its derivatives with other separate
and independent documents or works, in or on a volume of a storage or
distribution medium, is called an ``aggregate'' if the copyright
resulting from the compilation is not used to limit the legal rights
of the compilation's users beyond what the individual works permit.
When the Document is included in an aggregate, this License does not
apply to the other works in the aggregate which are not themselves
derivative works of the Document.
If the Cover Text requirement of section~3 is applicable to these
copies of the Document, then if the Document is less than one half of
the entire aggregate, the Document's Cover Texts may be placed on
covers that bracket the Document within the aggregate, or the
electronic equivalent of covers if the Document is in electronic form.
Otherwise they must appear on printed covers that bracket the whole
aggregate.
\begin{center}
{\Large\bf 8. TRANSLATION\par}
\end{center}
Translation is considered a kind of modification, so you may
distribute translations of the Document under the terms of section~4.
Replacing Invariant Sections with translations requires special
permission from their copyright holders, but you may include
translations of some or all Invariant Sections in addition to the
original versions of these Invariant Sections. You may include a
translation of this License, and all the license notices in the
Document, and any Warranty Disclaimers, provided that you also include
the original English version of this License and the original versions
of those notices and disclaimers. In case of a disagreement between
the translation and the original version of this License or a notice
or disclaimer, the original version will prevail.
If a section in the Document is Entitled ``Acknowledgements'',
``Dedications'', or ``History'', the requirement (section~4) to Preserve
its Title (section~1) will typically require changing the actual
title.
\begin{center}
{\Large\bf 9. TERMINATION\par}
\end{center}
You may not copy, modify, sublicense, or distribute the Document
except as expressly provided under this License. Any attempt
otherwise to copy, modify, sublicense, or distribute it is void, and
will automatically terminate your rights under this License.
However, if you cease all violation of this License, then your license
from a particular copyright holder is reinstated (a) provisionally,
unless and until the copyright holder explicitly and finally
terminates your license, and (b) permanently, if the copyright holder
fails to notify you of the violation by some reasonable means prior to
60 days after the cessation.
Moreover, your license from a particular copyright holder is
reinstated permanently if the copyright holder notifies you of the
violation by some reasonable means, this is the first time you have
received notice of violation of this License (for any work) from that
copyright holder, and you cure the violation prior to 30 days after
your receipt of the notice.
Termination of your rights under this section does not terminate the
licenses of parties who have received copies or rights from you under
this License. If your rights have been terminated and not permanently
reinstated, receipt of a copy of some or all of the same material does
not give you any rights to use it.
\begin{center}
{\Large\bf 10. FUTURE REVISIONS OF THIS LICENSE\par}
\end{center}
The Free Software Foundation may publish new, revised versions
of the GNU Free Documentation License from time to time. Such new
versions will be similar in spirit to the present version, but may
differ in detail to address new problems or concerns. See
\texttt{https://www.gnu.org/licenses/}.
Each version of the License is given a distinguishing version number.
If the Document specifies that a particular numbered version of this
License ``or any later version'' applies to it, you have the option of
following the terms and conditions either of that specified version or
of any later version that has been published (not as a draft) by the
Free Software Foundation. If the Document does not specify a version
number of this License, you may choose any version ever published (not
as a draft) by the Free Software Foundation. If the Document
specifies that a proxy can decide which future versions of this
License can be used, that proxy's public statement of acceptance of a
version permanently authorizes you to choose that version for the
Document.
\begin{center}
{\Large\bf 11. RELICENSING\par}
\end{center}
``Massive Multiauthor Collaboration Site'' (or ``MMC Site'') means any
World Wide Web server that publishes copyrightable works and also
provides prominent facilities for anybody to edit those works. A
public wiki that anybody can edit is an example of such a server. A
``Massive Multiauthor Collaboration'' (or ``MMC'') contained in the
site means any set of copyrightable works thus published on the MMC
site.
``CC-BY-SA'' means the Creative Commons Attribution-Share Alike 3.0
license published by Creative Commons Corporation, a not-for-profit
corporation with a principal place of business in San Francisco,
California, as well as future copyleft versions of that license
published by that same organization.
``Incorporate'' means to publish or republish a Document, in whole or
in part, as part of another Document.
An MMC is ``eligible for relicensing'' if it is licensed under this
License, and if all works that were first published under this License
somewhere other than this MMC, and subsequently incorporated in whole
or in part into the MMC, (1) had no cover texts or invariant sections,
and (2) were thus incorporated prior to November 1, 2008.
The operator of an MMC Site may republish an MMC contained in the site
under CC-BY-SA on the same site at any time before August 1, 2009,
provided the MMC is eligible for relicensing.
\begin{center}
{\Large\bf ADDENDUM: How to use this License for your documents\par}
\end{center}
To use this License in a document you have written, include a copy of
the License in the document and put the following copyright and
license notices just after the title page:
\bigskip
\begin{quote}
Copyright \copyright{} YEAR YOUR NAME.
Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.3
or any later version published by the Free Software Foundation;
with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts.
A copy of the license is included in the section entitled ``GNU
Free Documentation License''.
\end{quote}
\bigskip
If you have Invariant Sections, Front-Cover Texts and Back-Cover Texts,
replace the ``with \dots\ Texts.''\ line with this:
\bigskip
\begin{quote}
with the Invariant Sections being LIST THEIR TITLES, with the
Front-Cover Texts being LIST, and with the Back-Cover Texts being LIST.
\end{quote}
\bigskip
If you have Invariant Sections without Cover Texts, or some other
combination of the three, merge those two alternatives to suit the
situation.
If your document contains nontrivial examples of program code, we
recommend releasing these examples in parallel under your choice of
free software license, such as the GNU General Public License,
to permit their use in free software.
\end{document}
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