Adding upstream version 6.1.22-dfsg.upstream/6.1.22-dfsgupstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 1021 insertions, 0 deletions

diff --git a/doc/VBox-CodingGuidelines.cpp b/doc/VBox-CodingGuidelines.cpp
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+/* $Id: VBox-CodingGuidelines.cpp $ */
+/** @file
+ * VBox - Coding Guidelines.
+ */
+
+/*
+ * Copyright (C) 2006-2020 Oracle Corporation
+ *
+ * This file is part of VirtualBox Open Source Edition (OSE), as
+ * available from http://www.virtualbox.org. This file is free software;
+ * you can redistribute it and/or modify it under the terms of the GNU
+ * General Public License (GPL) as published by the Free Software
+ * Foundation, in version 2 as it comes in the "COPYING" file of the
+ * VirtualBox OSE distribution. VirtualBox OSE is distributed in the
+ * hope that it will be useful, but WITHOUT ANY WARRANTY of any kind.
+ */
+
+/** @page pg_vbox_guideline                 VBox Coding Guidelines
+ *
+ * The compulsory sections of these guidelines are to be followed in all of the
+ * VBox sources.  Please note that local guidelines in parts of the VBox source
+ * tree may promote the optional ones to compulsory status.  The VBox tree also
+ * contains some 3rd party sources where it is good to follow the local coding
+ * style while keeping these guidelines in mind.
+ *
+ * Contents:
+ *      - @ref sec_vbox_guideline_compulsory
+ *          - @ref sec_vbox_guideline_compulsory_sub64
+ *          - @ref sec_vbox_guideline_compulsory_cppmain
+ *          - @ref sec_vbox_guideline_compulsory_cppqtgui
+ *          - @ref sec_vbox_guideline_compulsory_xslt
+ *          - @ref sec_vbox_guideline_compulsory_doxygen
+ *          - @ref sec_vbox_guideline_compulsory_guest
+ *      - @ref sec_vbox_guideline_optional
+ *          - @ref sec_vbox_guideline_optional_layout
+ *          - @ref sec_vbox_guideline_optional_prefix
+ *          - @ref sec_vbox_guideline_optional_misc
+ *      - @ref sec_vbox_guideline_warnings
+ *          - @ref sec_vbox_guideline_warnings_signed_unsigned_compare
+ *      - @ref sec_vbox_guideline_svn
+ *
+ * Local guidelines overrides:
+ *      - src/VBox/VMM/:            @ref pg_vmm_guideline (src/VBox/VMM/Docs-CodingGuidelines.cpp)
+ *      - src/VBox/ValidationKit/:  @ref pg_validationkit_guideline  (src/VBox/ValidationKit/ValidationKitCodingGuidelines.cpp)
+ *      - src/VBox/Runtime/:        All of @ref sec_vbox_guideline_optional is mandatory.
+ *      - src/VBox/Main/:           @ref sec_vbox_guideline_compulsory_cppmain
+ *      - src/VBox/Frontends/VirtualBox/: @ref sec_vbox_guideline_compulsory_cppqtgui
+ *
+ *
+ * @section sec_vbox_guideline_compulsory       Compulsory
+ *
+ * <ul>
+ *
+ *   <li> The indentation size is 4 chars.
+ *
+ *   <li> Tabs are only ever used in makefiles.
+ *
+ *   <li> Use RT and VBOX types.
+ *
+ *   <li> Use Runtime functions.
+ *
+ *   <li> Use the standard bool, uintptr_t, intptr_t and [u]int[1-9+]_t types.
+ *
+ *   <li> Avoid using plain unsigned and int.
+ *
+ *   <li> Use static wherever possible. This makes the namespace less polluted
+ *        and avoids nasty name clash problems which can occur, especially on
+ *        Unix-like systems. (1)  It also simplifies locating callers when
+ *        changing it (single source file vs entire VBox tree).
+ *
+ *   <li> Public names are of the form Domain[Subdomain[]]Method, using mixed
+ *        casing to mark the words. The main domain is all uppercase.
+ *        (Think like java, mapping domain and subdomain to packages/classes.)
+ *
+ *   <li> Public names are always declared using the appropriate DECL macro. (2)
+ *
+ *   <li> Internal names starts with a lowercased main domain.
+ *
+ *   <li> Defines are all uppercase and separate words with underscore.
+ *        This applies to enum values too.
+ *
+ *   <li> Typedefs are all uppercase and contain no underscores to distinguish
+ *        them from defines.  Alternatively, all uppercase, separate words with
+ *        underscores and ending with '_T'.  The latter is not allowed in IPRT.
+ *
+ *   <li> Pointer typedefs start with 'P'. If pointer to const then 'PC'.
+ *
+ *   <li> Function typedefs start with 'FN'. If pointer to FN then 'PFN'.
+ *
+ *   <li> All files are case sensitive.
+ *
+ *   <li> Slashes are unix slashes ('/') runtime converts when necessary.
+ *
+ *   <li> char strings are UTF-8.
+ *
+ *   <li> Strings from any external source must be treated with utmost care as
+ *        they do not have to be valid UTF-8.  Only trust internal strings.
+ *
+ *   <li> All functions return VBox status codes. There are three general
+ *        exceptions from this:
+ *
+ *       <ol>
+ *             <li>Predicate functions. These are function which are boolean in
+ *                 nature and usage. They return bool. The function name will
+ *                 include 'Has', 'Is' or similar.
+ *             <li>Functions which by nature cannot possibly fail.
+ *                 These return void.
+ *             <li>"Get"-functions which return what they ask for.
+ *                 A get function becomes a "Query" function if there is any
+ *                 doubt about getting what is ask for.
+ *       </ol>
+ *
+ *   <li> VBox status codes have three subdivisions:
+ *         <ol>
+ *           <li> Errors, which are VERR_ prefixed and negative.
+ *           <li> Warnings, which are VWRN_ prefixed and positive.
+ *           <li> Informational, which are VINF_ prefixed and positive.
+ *        </ol>
+ *
+ *   <li> Platform/OS operation are generalized and put in the IPRT.
+ *
+ *   <li> Other useful constructs are also put in the IPRT.
+ *
+ *   <li> The code shall not cause compiler warnings. Check this on ALL
+ *        the platforms.
+ *
+ *   <li> The use of symbols leading with single or double underscores is
+ *        forbidden as that intrudes on reserved compiler/system namespace. (3)
+ *
+ *   <li> All files have file headers with $Id and a file tag which describes
+ *        the file in a sentence or two.
+ *        Note: Use the svn-ps.cmd/svn-ps.sh utility with the -a option to add
+ *              new sources with keyword expansion and exporting correctly
+ *              configured.
+ *
+ *   <li> All public functions are fully documented in Doxygen style using the
+ *        javadoc dialect (using the 'at' instead of the 'slash' as
+ *        commandprefix.)
+ *
+ *   <li> All structures in header files are described, including all their
+ *        members. (Doxygen style, of course.)
+ *
+ *   <li> All modules have a documentation '\@page' in the main source file
+ *        which describes the intent and actual implementation.
+ *
+ *   <li> Code which is doing things that are not immediately comprehensible
+ *        shall include explanatory comments.
+ *
+ *   <li> Documentation and comments are kept up to date.
+ *
+ *   <li> Headers in /include/VBox shall not contain any slash-slash C++
+ *        comments, only ANSI C comments!
+ *
+ *   <li> Comments on \#else indicates what begins while the comment on a
+ *        \#endif indicates what ended.  Only add these when there are more than
+ *        a few lines (6-10) of \#ifdef'ed code, otherwise they're just clutter.
+ *
+ *   <li> \#ifdefs around a single function shall be tight, i.e. no empty
+ *        lines between it and the function documentation and body.
+ *
+ *   <li> \#ifdefs around more than one function shall be relaxed, i.e. leave at
+ *        least one line before the first function's documentation comment and
+ *        one line after the end of the last function.
+ *
+ *   <li> No 'else' after if block ending with 'return', 'break', or 'continue'.
+ *
+ *   <li> The term 'last' is inclusive, whereas the term 'end' is exclusive.
+ *
+ *   <li> Go through all of this: https://www.slideshare.net/olvemaudal/deep-c/
+ *
+ *   <li> Avoid throwing exceptions, always prefer returning statuses.
+ *        Crappy exception handling is rewared by a glass of water in the face.
+ *
+ * </ul>
+ *
+ * (1) It is common practice on Unix to have a single symbol namespace for an
+ *     entire process. If one is careless symbols might be resolved in a
+ *     different way that one expects, leading to weird problems.
+ *
+ * (2) This is common practice among most projects dealing with modules in
+ *     shared libraries. The Windows / PE __declspect(import) and
+ *     __declspect(export) constructs are the main reason for this.
+ *     OTOH, we do perhaps have a bit too detailed graining of this in VMM...
+ *
+ * (3) There are guys out there grepping public sources for symbols leading with
+ *     single and double underscores as well as gotos and other things
+ *     considered bad practice.  They'll post statistics on how bad our sources
+ *     are on some mailing list, forum or similar.
+ *
+ *
+ * @subsection sec_vbox_guideline_compulsory_sub64  64-bit and 32-bit
+ *
+ * Here are some amendments which address 64-bit vs. 32-bit portability issues.
+ *
+ * Some facts first:
+ *
+ * <ul>
+ *
+ *   <li> On 64-bit Windows the type long remains 32-bit. On nearly all other
+ *        64-bit platforms long is 64-bit.
+ *
+ *   <li> On all 64-bit platforms we care about, int is 32-bit, short is 16 bit
+ *        and char is 8-bit.
+ *        (I don't know about any platforms yet where this isn't true.)
+ *
+ *   <li> size_t, ssize_t, uintptr_t, ptrdiff_t and similar are all 64-bit on
+ *        64-bit platforms. (These are 32-bit on 32-bit platforms.)
+ *
+ *   <li> There is no inline assembly support in the 64-bit Microsoft compilers.
+ *
+ * </ul>
+ *
+ * Now for the guidelines:
+ *
+ * <ul>
+ *
+ *   <li> Never, ever, use int, long, ULONG, LONG, DWORD or similar to cast a
+ *        pointer to integer.  Use uintptr_t or intptr_t. If you have to use
+ *        NT/Windows types, there is the choice of ULONG_PTR and DWORD_PTR.
+ *
+ *   <li> Avoid where ever possible the use of the types 'long' and 'unsigned
+ *        long' as these differs in size between windows and the other hosts
+ *        (see above).
+ *
+ *   <li> RT_OS_WINDOWS is defined to indicate Windows. Do not use __WIN32__,
+ *        __WIN64__ and __WIN__ because they are all deprecated and scheduled
+ *        for removal (if not removed already). Do not use the compiler
+ *        defined _WIN32, _WIN64, or similar either. The bitness can be
+ *        determined by testing ARCH_BITS.
+ *        Example:
+ *        @code
+ *              #ifdef RT_OS_WINDOWS
+ *              // call win32/64 api.
+ *              #endif
+ *              #ifdef RT_OS_WINDOWS
+ *              # if ARCH_BITS == 64
+ *              // call win64 api.
+ *              # else  // ARCH_BITS == 32
+ *              // call win32 api.
+ *              # endif // ARCH_BITS == 32
+ *              #else  // !RT_OS_WINDOWS
+ *              // call posix api
+ *              #endif // !RT_OS_WINDOWS
+ *        @endcode
+ *
+ *   <li> There are RT_OS_xxx defines for each OS, just like RT_OS_WINDOWS
+ *        mentioned above. Use these defines instead of any predefined
+ *        compiler stuff or defines from system headers.
+ *
+ *   <li> RT_ARCH_X86 is defined when compiling for the x86 the architecture.
+ *        Do not use __x86__, __X86__, __[Ii]386__, __[Ii]586__, or similar
+ *        for this purpose.
+ *
+ *   <li> RT_ARCH_AMD64 is defined when compiling for the AMD64 architecture.
+ *        Do not use __AMD64__, __amd64__ or __x64_86__.
+ *
+ *   <li> Take care and use size_t when you have to, esp. when passing a pointer
+ *        to a size_t as a parameter.
+ *
+ *   <li> Be wary of type promotion to (signed) integer. For example the
+ *        following will cause u8 to be promoted to int in the shift, and then
+ *        sign extended in the assignment 64-bit:
+ *        @code
+ *              uint8_t u8 = 0xfe;
+ *              uint64_t u64 = u8 << 24;
+ *              // u64 == 0xfffffffffe000000
+ *        @endcode
+ *
+ * </ul>
+ *
+ * @subsubsection sec_vbox_guideline_compulsory_sub64_comp  Comparing the GCC and MSC calling conventions
+ *
+ * GCC expects the following (cut & past from page 20 in the ABI draft 0.96):
+ *
+ * @verbatim
+    %rax     temporary register; with variable arguments passes information about the
+             number of SSE registers used; 1st return register.
+             [Not preserved]
+    %rbx     callee-saved register; optionally used as base pointer.
+             [Preserved]
+    %rcx     used to pass 4th integer argument to functions.
+             [Not preserved]
+    %rdx     used to pass 3rd argument to functions; 2nd return register
+             [Not preserved]
+    %rsp     stack pointer
+             [Preserved]
+    %rbp     callee-saved register; optionally used as frame pointer
+             [Preserved]
+    %rsi     used to pass 2nd argument to functions
+             [Not preserved]
+    %rdi     used to pass 1st argument to functions
+             [Not preserved]
+    %r8      used to pass 5th argument to functions
+             [Not preserved]
+    %r9      used to pass 6th argument to functions
+             [Not preserved]
+    %r10     temporary register, used for passing a function's static chain
+             pointer [Not preserved]
+    %r11     temporary register
+             [Not preserved]
+    %r12-r15 callee-saved registers
+             [Preserved]
+    %xmm0-%xmm1  used to pass and return floating point arguments
+             [Not preserved]
+    %xmm2-%xmm7  used to pass floating point arguments
+             [Not preserved]
+    %xmm8-%xmm15 temporary registers
+             [Not preserved]
+    %mmx0-%mmx7  temporary registers
+             [Not preserved]
+    %st0     temporary register; used to return long double arguments
+             [Not preserved]
+    %st1     temporary registers; used to return long double arguments
+             [Not preserved]
+    %st2-%st7 temporary registers
+             [Not preserved]
+    %fs      Reserved for system use (as thread specific data register)
+             [Not preserved]
+   @endverbatim
+ *
+ * Direction flag is preserved as cleared.
+ * The stack must be aligned on a 16-byte boundary before the 'call/jmp' instruction.
+ *
+ * MSC expects the following:
+ * @verbatim
+    rax      return value, not preserved.
+    rbx      preserved.
+    rcx      1st argument, integer, not preserved.
+    rdx      2nd argument, integer, not preserved.
+    rbp      preserved.
+    rsp      preserved.
+    rsi      preserved.
+    rdi      preserved.
+    r8       3rd argument, integer, not preserved.
+    r9       4th argument, integer, not preserved.
+    r10      scratch register, not preserved.
+    r11      scratch register, not preserved.
+    r12-r15  preserved.
+    xmm0     1st argument, fp, return value, not preserved.
+    xmm1     2st argument, fp, not preserved.
+    xmm2     3st argument, fp, not preserved.
+    xmm3     4st argument, fp, not preserved.
+    xmm4-xmm5    scratch, not preserved.
+    xmm6-xmm15   preserved.
+   @endverbatim
+ *
+ * Dunno what the direction flag is...
+ * The stack must be aligned on a 16-byte boundary before the 'call/jmp' instruction.
+ *
+ *
+ * @subsection sec_vbox_guideline_compulsory_cppmain   C++ guidelines for Main
+ *
+ * Since the Main API code is a large amount of C++ code, it is allowed but
+ * not required to use C++ style comments (as permanent comments, beyond the
+ * temporary use allowed by the general coding guideline).  This is a weak
+ * preference, i.e. large scale comment style changes are not encouraged.
+ *
+ * Main is currently (2009) full of hard-to-maintain code that uses complicated
+ * templates. The new mid-term goal for Main is to have less custom templates
+ * instead of more for the following reasons:
+ *
+ * <ul>
+ *
+ *   <li>  Template code is harder to read and understand. Custom templates create
+ *         territories which only the code writer understands.
+ *
+ *   <li>  Errors in using templates create terrible C++ compiler messages.
+ *
+ *   <li>  Template code is really hard to look at in a debugger.
+ *
+ *   <li>  Templates slow down the compiler a lot.
+ *
+ * </ul>
+ *
+ * In particular, the following bits should be considered deprecated and should
+ * NOT be used in new code:
+ *
+ * <ul>
+ *
+ *   <li>  everything in include/iprt/cpputils.h (auto_ref_ptr, exception_trap_base,
+ *         char_auto_ptr and friends)
+ *
+ * </ul>
+ *
+ * Generally, in many cases, a simple class with a proper destructor can achieve
+ * the same effect as a 1,000-line template include file, and the code is
+ * much more accessible that way.
+ *
+ * Using standard STL templates like std::list, std::vector and std::map is OK.
+ * Exceptions are:
+ *
+ * <ul>
+ *
+ *   <li>  Guest Additions because we don't want to link against libstdc++ there.
+ *
+ *   <li>  std::string should not be used because we have iprt::MiniString and
+ *     com::Utf8Str which can convert efficiently with COM's UTF-16 strings.
+ *
+ *   <li>  std::auto_ptr<> in general; that part of the C++ standard is just broken.
+ *     Write a destructor that calls delete.
+ *
+ * </ul>
+ *
+ * @subsection sec_vbox_guideline_compulsory_cppqtgui   C++ guidelines for the Qt GUI
+ *
+ * The Qt GUI is currently (2010) on its way to become more compatible to the
+ * rest of VirtualBox coding style wise. From now on, all the coding style
+ * rules described in this file are also mandatory for the Qt GUI. Additionally
+ * the following rules should be respected:
+ *
+ * <ul>
+ *
+ *   <li> GUI classes which correspond to GUI tasks should be prefixed by UI (no VBox anymore)
+ *
+ *   <li> Classes which extents some of the Qt classes should be prefix by QI
+ *
+ *   <li> General task classes should be prefixed by C
+ *
+ *   <li> Slots are prefixed by slt -> sltName
+ *
+ *   <li> Signals are prefixed by sig -> sigName
+ *
+ *   <li> Use Qt classes for lists, strings and so on, the use of STL classes should
+ *   be avoided
+ *
+ *   <li> All files like .cpp, .h, .ui, which belong together are located in the
+ *   same directory and named the same
+ *
+ * </ul>
+ *
+ *
+ * @subsection sec_vbox_guideline_compulsory_xslt  XSLT
+ *
+ * XSLT (eXtensible Stylesheet Language Transformations) is used quite a bit in
+ * the Main API area of VirtualBox to generate sources and bindings to that API.
+ * There are a couple of common pitfalls worth mentioning:
+ *
+ * <ul>
+ *
+ *   <li> Never do repeated //interface[\@name=...] and //enum[\@name=...] lookups
+ *        because they are expensive. Instead delcare xsl:key elements for these
+ *        searches and do the lookup using the key() function. xsltproc uses
+ *        (per current document) hash tables for each xsl:key, i.e. very fast.
+ *
+ *   <li> When output type is 'text' make sure to call xsltprocNewlineOutputHack
+ *        from typemap-shared.inc.xsl every few KB of output, or xsltproc will
+ *        end up wasting all the time reallocating the output buffer.
+ *
+ * </ul>
+ *
+ *
+ * @subsection sec_vbox_guideline_compulsory_doxygen    Doxygen Comments
+ *
+ * As mentioned above, we shall use doxygen/javadoc style commenting of public
+ * functions, typedefs, classes and such.  It is mandatory to use this style
+ * everywhere!
+ *
+ * A couple of hints on how to best write doxygen comments:
+ *
+ * <ul>
+ *
+ *   <li> A good class, method, function, structure or enum doxygen comment
+ *        starts with a one line sentence giving a brief description of the
+ *        item.  Details comes in a new paragraph (after blank line).
+ *
+ *   <li> Except for list generators like \@todo, \@cfgm, \@gcfgm and others,
+ *        all doxygen comments are related to things in the code.  So, for
+ *        instance you DO NOT add a doxygen \@note comment in the middle of a
+ *        because you've got something important to note, you add a normal
+ *        comment like 'Note! blah, very importan blah!'
+ *
+ *   <li> We do NOT use TODO/XXX/BUGBUG or similar markers in the code to flag
+ *        things needing fixing later, we always use \@todo doxygen comments.
+ *
+ *   <li> There is no colon after the \@todo.  And it is ALWAYS in a doxygen
+ *        comment.
+ *
+ *   <li> The \@retval tag is used to explain status codes a method/function may
+ *        returns.  It is not used to describe output parameters, that is done
+ *        using the \@param or \@param[out] tag.
+ *
+ * </ul>
+ *
+ * See https://www.stack.nl/~dimitri/doxygen/manual/index.html for the official
+ * doxygen documention.
+ *
+ *
+ *
+ * @subsection sec_vbox_guideline_compulsory_guest  Handling of guest input
+ *
+ * First, guest input should ALWAYS be consider to be TOXIC and constructed with
+ * MALICIOUS intent!  Max paranoia level!
+ *
+ * Second, when getting inputs from memory shared with the guest, be EXTREMELY
+ * careful to not re-read input from shared memory after validating it, because
+ * that will create TOCTOU problems. So, after reading input from shared memory
+ * always use the RT_UNTRUSTED_NONVOLATILE_COPY_FENCE() macro.  For more details
+ * on TOCTOU: https://en.wikipedia.org/wiki/Time_of_check_to_time_of_use
+ *
+ * Thirdly, considering the recent speculation side channel issues, spectre v1
+ * in particular, we would like to be ready for future screwups.   This means
+ * having input validation in a separate block of code that ends with one (or
+ * more) RT_UNTRUSTED_VALIDATED_FENCE().
+ *
+ * So the rules:
+ *
+ * <ul>
+ *
+ *   <li> Mark all pointers to shared memory with RT_UNTRUSTED_VOLATILE_GUEST.
+ *
+ *   <li> Copy volatile data into local variables or heap before validating
+ *        them (see RT_COPY_VOLATILE() and RT_BCOPY_VOLATILE().
+ *
+ *   <li> Place RT_UNTRUSTED_NONVOLATILE_COPY_FENCE() after a block copying
+ *        volatile data.
+ *
+ *   <li> Always validate untrusted inputs in a block ending with a
+ *        RT_UNTRUSTED_VALIDATED_FENCE().
+ *
+ *   <li> Use the ASSERT_GUEST_XXXX macros from VBox/AssertGuest.h to validate
+ *        guest input.  (Do NOT use iprt/assert.h macros.)
+ *
+ *   <li> Validation of an input B may require using another input A to look up
+ *        some data, in which case its necessary to insert an
+ *        RT_UNTRUSTED_VALIDATED_FENCE() after validating A and before A is used
+ *        for the lookup.
+ *
+ *        For example A is a view identifier, idView, and B is an offset into
+ *        the view's framebuffer area, offView.  To validate offView (B) it is
+ *        necessary to get the size of the views framebuffer region:
+ *        @code
+ *              uint32_t const idView  = pReq->idView;   // A
+ *              uint32_t const offView = pReq->offView;  // B
+ *              RT_UNTRUSTED_NONVOLATILE_COPY_FENCE();
+ *
+ *              ASSERT_GUEST_RETURN(idView < pThis->cView,
+ *                                  VERR_INVALID_PARAMETER);
+ *              RT_UNTRUSTED_VALIDATED_FENCE();
+ *              const MYVIEW *pView = &pThis->aViews[idView];
+ *              ASSERT_GUEST_RETURN(offView < pView->cbFramebufferArea,
+ *                                  VERR_OUT_OF_RANGE);
+ *              RT_UNTRUSTED_VALIDATED_FENCE();
+ *        @endcode
+ *
+ *   <li> Take care to make sure input check are not subject to integer overflow problems.
+ *
+ *        For instance when validating an area, you must not just add cbDst + offDst
+ *        and check against pThis->offEnd or something like that.  Rather do:
+ *        @code
+ *              uint32_t const offDst = pReq->offDst;
+ *              uint32_t const cbDst  = pReq->cbDst;
+ *              RT_UNTRUSTED_NONVOLATILE_COPY_FENCE();
+ *
+ *              ASSERT_GUEST_RETURN(   cbDst  <= pThis->cbSrc
+ *                                  && offDst < pThis->cbSrc - cbDst,
+ *                                  VERR_OUT_OF_RANGE);
+ *              RT_UNTRUSTED_VALIDATED_FENCE();
+ *        @endcode
+ *
+ *   <li> Input validation does not only apply to shared data cases, but also to
+ *        I/O port and MMIO handlers.
+ *
+ *   <li> Ditto for kernel drivers working with usermode inputs.
+ *
+ * </ul>
+ *
+ *
+ * Problem patterns:
+ *   - https://en.wikipedia.org/wiki/Time_of_check_to_time_of_use
+ *   - https://googleprojectzero.blogspot.de/2018/01/reading-privileged-memory-with-side.html
+ *     (Variant 1 only).
+ *   - https://en.wikipedia.org/wiki/Integer_overflow
+ *
+ *
+ *
+ * @section sec_vbox_guideline_optional         Optional
+ *
+ * First part is the actual coding style and all the prefixes.  The second part
+ * is a bunch of good advice.
+ *
+ *
+ * @subsection sec_vbox_guideline_optional_layout   The code layout
+ *
+ * <ul>
+ *
+ *   <li> Max line length is 130 chars.  Exceptions are table-like
+ *        code/initializers and Log*() statements (don't waste unnecessary
+ *        vertical space on debug logging).
+ *
+ *   <li> Comments should try stay within the usual 80 columns as these are
+ *        denser and too long lines may be harder to read.
+ *
+ *   <li> Curly brackets are not indented.  Example:
+ *        @code
+ *              if (true)
+ *              {
+ *                  Something1();
+ *                  Something2();
+ *              }
+ *              else
+ *              {
+ *                  SomethingElse1().
+ *                  SomethingElse2().
+ *              }
+ *        @endcode
+ *
+ *   <li> Space before the parentheses when it comes after a C keyword.
+ *
+ *   <li> No space between argument and parentheses. Exception for complex
+ *        expression.  Example:
+ *        @code
+ *              if (PATMR3IsPatchGCAddr(pVM, GCPtr))
+ *        @endcode
+ *
+ *   <li> The else of an if is always the first statement on a line. (No curly
+ *        stuff before it!)
+ *
+ *   <li> else and if go on the same line if no { compound statement }
+ *        follows the if.  Example:
+ *        @code
+ *              if (fFlags & MYFLAGS_1)
+ *                  fFlags &= ~MYFLAGS_10;
+ *              else if (fFlags & MYFLAGS_2)
+ *              {
+ *                  fFlags &= ~MYFLAGS_MASK;
+ *                  fFlags |= MYFLAGS_5;
+ *              }
+ *              else if (fFlags & MYFLAGS_3)
+ *        @endcode
+ *
+ *   <li> Slightly complex boolean expressions are split into multiple lines,
+ *        putting the operators first on the line and indenting it all according
+ *        to the nesting of the expression. The purpose is to make it as easy as
+ *        possible to read.  Example:
+ *        @code
+ *              if (    RT_SUCCESS(rc)
+ *                  ||  (fFlags & SOME_FLAG))
+ *        @endcode
+ *
+ *   <li> When 'if' or  'while' statements gets long, the closing parentheses
+ *        goes right below the opening parentheses.  This may be applied to
+ *        sub-expression.  Example:
+ *        @code
+ *              if (    RT_SUCCESS(rc)
+ *                  ||  (   fSomeStuff
+ *                       && fSomeOtherStuff
+ *                       && fEvenMoreStuff
+ *                      )
+ *                  ||  SomePredicateFunction()
+ *                 )
+ *              {
+ *                  ...
+ *              }
+ *        @endcode
+ *
+ *   <li> The case is indented from the switch (to avoid having the braces for
+ *        the 'case' at the same level as the 'switch' statement).
+ *
+ *   <li> If a case needs curly brackets they contain the entire case, are not
+ *        indented from the case, and the break or return is placed inside them.
+ *        Example:
+ *        @code
+ *              switch (pCur->eType)
+ *              {
+ *                  case PGMMAPPINGTYPE_PAGETABLES:
+ *                  {
+ *                      unsigned iPDE = pCur->GCPtr >> PGDIR_SHIFT;
+ *                      unsigned iPT = (pCur->GCPtrEnd - pCur->GCPtr) >> PGDIR_SHIFT;
+ *                      while (iPT-- > 0)
+ *                          if (pPD->a[iPDE + iPT].n.u1Present)
+ *                              return VERR_HYPERVISOR_CONFLICT;
+ *                      break;
+ *                  }
+ *              }
+ *        @endcode
+ *
+ *   <li> In a do while construction, the while is on the same line as the
+ *        closing "}" if any are used.
+ *        Example:
+ *        @code
+ *              do
+ *              {
+ *                  stuff;
+ *                  i--;
+ *              } while (i > 0);
+ *        @endcode
+ *
+ *   <li> Comments are in C style.  C++ style comments are used for temporary
+ *        disabling a few lines of code.
+ *
+ *   <li> No unnecessary parentheses in expressions (just don't over do this
+ *        so that gcc / msc starts bitching). Find a correct C/C++ operator
+ *        precedence table if needed.
+ *
+ *   <li> 'for (;;)' is preferred over 'while (true)' and 'while (1)'.
+ *
+ *   <li> Parameters are indented to the start parentheses when breaking up
+ *        function calls, declarations or prototypes.  (This is in line with
+ *        how 'if', 'for' and 'while' statements are done as well.) Example:
+ *        @code
+ *              RTPROCESS hProcess;
+ *              int rc = RTProcCreateEx(papszArgs[0],
+ *                                      papszArgs,
+ *                                      RTENV_DEFAULT,
+ *                                      fFlags,
+ *                                      NULL,           // phStdIn
+ *                                      NULL,           // phStdOut
+ *                                      NULL,           // phStdErr
+ *                                      NULL,           // pszAsUser
+ *                                      NULL,           // pszPassword
+ *                                      NULL,           // pExtraData
+ *                                      &hProcess);
+ *        @endcode
+ *
+ *   <li> That Dijkstra is dead is no excuse for using gotos.
+ *
+ *   <li> Using do-while-false loops to avoid gotos is considered very bad form.
+ *        They create hard to read code.  They tend to be either too short (i.e.
+ *        pointless) or way to long (split up the function already), making
+ *        tracking the state is difficult and prone to bugs.  Also, they cause
+ *        the compiler to generate suboptimal code, because the break branches
+ *        are by preferred over the main code flow (MSC has no branch hinting!).
+ *        Instead, do make use the 130 columns (i.e. nested ifs) and split
+ *        the code up into more functions!
+ *
+ *   <li> Avoid code like
+ *        @code
+ *              int foo;
+ *              int rc;
+ *              ...
+ *              rc = FooBar();
+ *              if (RT_SUCCESS(rc))
+ *              {
+ *                  foo = getFoo();
+ *                  ...
+ *                  pvBar = RTMemAlloc(sizeof(*pvBar));
+ *                  if (!pvBar)
+ *                     rc = VERR_NO_MEMORY;
+ *              }
+ *              if (RT_SUCCESS(rc))
+ *              {
+ *                  buzz = foo;
+ *                  ...
+ *              }
+ *        @endcode
+ *        The intention of such code is probably to save some horizontal space
+ *        but unfortunately it's hard to read and the scope of certain varables
+ *        (e.g. foo in this example) is not optimal. Better use the following
+ *        style:
+ *        @code
+ *              int rc;
+ *              ...
+ *              rc = FooBar();
+ *              if (RT_SUCCESS(rc))
+ *              {
+ *                  int foo = getFoo();
+ *                  ...
+ *                  pvBar = RTMemAlloc(sizeof(*pvBar));
+ *                  if (pvBar)
+ *                  {
+ *                      buzz = foo;
+ *                      ...
+ *                  }
+ *                  else
+ *                      rc = VERR_NO_MEMORY;
+ *              }
+ *        @endcode
+ *
+ * </ul>
+ *
+ * @subsection sec_vbox_guideline_optional_prefix   Variable / Member Prefixes
+ *
+ * Prefixes are meant to provide extra context clues to a variable/member, we
+ * therefore avoid using prefixes that just indicating the type if a better
+ * choice is available.
+ *
+ *
+ * The prefixes:
+ *
+ * <ul>
+ *
+ *   <li> The 'g_' (or 'g') prefix means a global variable, either on file or module level.
+ *
+ *   <li> The 's_' (or 's') prefix means a static variable inside a function or
+ *        class.  This is not used for static variables on file level, use 'g_'
+ *        for those (logical, right).
+ *
+ *   <li> The 'm_' (or 'm') prefix means a class data member.
+ *
+ *        In new code in Main, use "m_" (and common sense).  As an exception,
+ *        in Main, if a class encapsulates its member variables in an anonymous
+ *        structure which is declared in the class, but defined only in the
+ *        implementation (like this: 'class X { struct Data; Data *m; }'), then
+ *        the pointer to that struct is called 'm' itself and its members then
+ *        need no prefix, because the members are accessed with 'm->member'
+ *        already which is clear enough.
+ *
+ *   <li> The 'a_' prefix means a parameter (argument) variable.  This is
+ *        sometimes written 'a' in parts of the source code that does not use
+ *        the array prefix.
+ *
+ *   <li> The 'p' prefix means pointer.  For instance 'pVM' is pointer to VM.
+ *
+ *   <li> The 'r' prefix means that something is passed by reference.
+ *
+ *   <li> The 'k' prefix means that something is a constant.  For instance
+ *        'enum { kStuff };'.  This is usually not used in combination with
+ *        'p', 'r' or any such thing, it's main main use is to make enums
+ *        easily identifiable.
+ *
+ *   <li> The 'a' prefix means array.  For instance 'aPages' could be read as
+ *        array of pages.
+ *
+ *   <li> The 'c' prefix means count.  For instance 'cbBlock' could be read,
+ *        count of bytes in block. (1)
+ *
+ *   <li> The 'cx' prefix means width (count of 'x' units).
+ *
+ *   <li> The 'cy' prefix means height (count of 'y' units).
+ *
+ *   <li> The 'x', 'y' and 'z' prefix refers to the x-, y- , and z-axis
+ *        respectively.
+ *
+ *   <li> The 'off' prefix means offset.
+ *
+ *   <li> The 'i' or 'idx' prefixes usually means index.  Although the 'i' one
+ *        can sometimes just mean signed integer.
+ *
+ *   <li> The 'i[1-9]+' prefix means a fixed bit size variable.  Frequently
+ *        used with the int[1-9]+_t types where the width is really important.
+ *        In most cases 'i' is more appropriate.  [type]
+ *
+ *   <li> The 'e' (or 'enm') prefix means enum.
+ *
+ *   <li> The 'u' prefix usually means unsigned integer.  Exceptions follows.
+ *
+ *   <li> The 'u[1-9]+' prefix means a fixed bit size variable.  Frequently
+ *        used with the uint[1-9]+_t types and with bitfields where the width is
+ *        really important.  In most cases 'u' or 'b' (byte) would be more
+ *        appropriate.  [type]
+ *
+ *   <li> The 'b' prefix means byte or bytes.  [type]
+ *
+ *   <li> The 'f' prefix means flags.  Flags are unsigned integers of some kind
+ *        or booleans.
+ *
+ *   <li> TODO: need prefix for real float.  [type]
+ *
+ *   <li> The 'rd' prefix means real double and is used for 'double' variables.
+ *        [type]
+ *
+ *   <li> The 'lrd' prefix means long real double and is used for 'long double'
+ *        variables. [type]
+ *
+ *   <li> The 'ch' prefix means a char, the (signed) char type.  [type]
+ *
+ *   <li> The 'wc' prefix means a wide/windows char, the RTUTF16 type.  [type]
+ *
+ *   <li> The 'uc' prefix means a Unicode Code point, the RTUNICP type.  [type]
+ *
+ *   <li> The 'uch' prefix means unsigned char.  It's rarely used.  [type]
+ *
+ *   <li> The 'sz' prefix means zero terminated character string (array of
+ *        chars). (UTF-8)
+ *
+ *   <li> The 'wsz' prefix means zero terminated wide/windows character string
+ *        (array of RTUTF16).
+ *
+ *   <li> The 'usz' prefix means zero terminated Unicode string (array of
+ *        RTUNICP).
+ *
+ *   <li> The 'str' prefix means C++ string; either a std::string or, in Main,
+ *        a Utf8Str or, in Qt, a QString.  When used with 'p', 'r', 'a' or 'c'
+ *        the first letter should be capitalized.
+ *
+ *   <li> The 'bstr' prefix, in Main, means a UTF-16 Bstr. When used with 'p',
+ *        'r', 'a' or 'c' the first letter should be capitalized.
+ *
+ *   <li> The 'pfn' prefix means pointer to function. Common usage is 'pfnCallback'
+ *        and such like.
+ *
+ *   <li> The 'psz' prefix is a combination of 'p' and 'sz' and thus means
+ *        pointer to a zero terminated character string. (UTF-8)
+ *
+ *   <li> The 'pcsz' prefix is used to indicate constant string pointers in
+ *        parts of the code.  Most code uses 'psz' for const and non-const
+ *        string pointers, so please ignore this one.
+ *
+ *   <li> The 'l' prefix means (signed) long.  We try avoid using this,
+ *        expecially with the 'LONG' types in Main as these are not 'long' on
+ *        64-bit non-Windows platforms and can cause confusion. Alternatives:
+ *        'i' or 'i32'.  [type]
+ *
+ *   <li> The 'ul' prefix means unsigned long.  We try avoid using this,
+ *        expecially with the 'ULONG' types in Main as these are not 'unsigned
+ *        long' on 64-bit non-Windows platforms and can cause confusion.
+ *        Alternatives: 'u' or 'u32'.  [type]
+ *
+ * </ul>
+ *
+ * (1)  Except in the occasional 'pcsz' prefix, the 'c' prefix is never ever
+ *      used in the meaning 'const'.
+ *
+ *
+ * @subsection sec_vbox_guideline_optional_misc     Misc / Advice / Stuff
+ *
+ * <ul>
+ *
+ *   <li> When writing code think as the reader.
+ *
+ *   <li> When writing code think as the compiler. (2)
+ *
+ *   <li> When reading code think as if it's full of bugs - find them and fix them.
+ *
+ *   <li> Pointer within range tests like:
+ *        @code
+ *          if ((uintptr_t)pv >= (uintptr_t)pvBase && (uintptr_t)pv < (uintptr_t)pvBase + cbRange)
+ *        @endcode
+ *        Can also be written as (assuming cbRange unsigned):
+ *        @code
+ *          if ((uintptr_t)pv - (uintptr_t)pvBase < cbRange)
+ *        @endcode
+ *        Which is shorter and potentially faster. (1)
+ *
+ *   <li> Avoid unnecessary casting. All pointers automatically cast down to
+ *        void *, at least for non class instance pointers.
+ *
+ *   <li> It's very very bad practise to write a function larger than a
+ *        screen full (1024x768) without any comprehensibility and explaining
+ *        comments.
+ *
+ *   <li> More to come....
+ *
+ * </ul>
+ *
+ * (1)  Important, be very careful with the casting. In particular, note that
+ *      a compiler might treat pointers as signed (IIRC).
+ *
+ * (2)  "A really advanced hacker comes to understand the true inner workings of
+ *      the machine - he sees through the language he's working in and glimpses
+ *      the secret functioning of the binary code - becomes a Ba'al Shem of
+ *      sorts."   (Neal Stephenson "Snow Crash")
+ *
+ *
+ *
+ * @section sec_vbox_guideline_warnings     Compiler Warnings
+ *
+ * The code should when possible compile on all platforms and compilers without any
+ * warnings. That's a nice idea, however, if it means making the code harder to read,
+ * less portable, unreliable or similar, the warning should not be fixed.
+ *
+ * Some of the warnings can seem kind of innocent at first glance. So, let's take the
+ * most common ones and explain them.
+ *
+ *
+ * @subsection sec_vbox_guideline_warnings_signed_unsigned_compare      Signed / Unsigned Compare
+ *
+ * GCC says: "warning: comparison between signed and unsigned integer expressions"
+ * MSC says: "warning C4018: '<|<=|==|>=|>' : signed/unsigned mismatch"
+ *
+ * The following example will not output what you expect:
+@code
+#include <stdio.h>
+int main()
+{
+    signed long a = -1;
+    unsigned long b = 2294967295;
+    if (a < b)
+        printf("%ld < %lu: true\n", a, b);
+    else
+        printf("%ld < %lu: false\n", a, b);
+    return 0;
+}
+@endcode
+ * If I understood it correctly, the compiler will convert a to an
+ * unsigned long before doing the compare.
+ *
+ *
+ *
+ * @section sec_vbox_guideline_svn          Subversion Commit Rules
+ *
+ *
+ * Before checking in:
+ *
+ * <ul>
+ *
+ *   <li> Check Tinderbox and make sure the tree is green across all platforms. If it's
+ *        red on a platform, don't check in. If you want, warn in the \#vbox channel and
+ *        help make the responsible person fix it.
+ *        NEVER CHECK IN TO A BROKEN BUILD.
+ *
+ *   <li> When checking in keep in mind that a commit is atomic and that the Tinderbox and
+ *        developers are constantly checking out the tree. Therefore do not split up the
+ *        commit unless it's into 100% independent parts. If you need to split it up in order
+ *        to have sensible commit comments, make the sub-commits as rapid as possible.
+ *
+ *   <li> If you make a user visible change, such as fixing a reported bug,
+ *        make sure you add an entry to doc/manual/user_ChangeLogImpl.xml.
+ *
+ *   <li> If you are adding files make sure set the right attributes.
+ *        svn-ps.sh/cmd was created for this purpose, please make use of it.
+ *
+ * </ul>
+ *
+ * After checking in:
+ *
+ * <ul>
+ *
+ *   <li> After checking-in, you watch Tinderbox until your check-ins clear. You do not
+ *        go home. You do not sleep. You do not log out or experiment with drugs. You do
+ *        not become unavailable. If you break the tree, add a comment saying that you're
+ *        fixing it. If you can't fix it and need help, ask in the \#innotek channel or back
+ *        out the change.
+ *
+ * </ul>
+ *
+ * (Inspired by mozilla tree rules.)
+ *
+ *
+ */
+