This is gdb.info, produced by makeinfo version 4.8 from ./gdb.texinfo. INFO-DIR-SECTION Software development START-INFO-DIR-ENTRY * Gdb: (gdb). The GNU debugger. END-INFO-DIR-ENTRY Copyright (C) 1988, 1989, 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010 Free Software Foundation, Inc. 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 the Invariant Sections being "Free Software" and "Free Software Needs Free Documentation", with the Front-Cover Texts being "A GNU Manual," and with the Back-Cover Texts as in (a) below. (a) The FSF's Back-Cover Text is: "You are free to copy and modify this GNU Manual. Buying copies from GNU Press supports the FSF in developing GNU and promoting software freedom." This file documents the GNU debugger GDB. This is the Ninth Edition, of `Debugging with GDB: the GNU Source-Level Debugger' for GDB (GDB) Version 7.2. Copyright (C) 1988, 1989, 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010 Free Software Foundation, Inc. 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 the Invariant Sections being "Free Software" and "Free Software Needs Free Documentation", with the Front-Cover Texts being "A GNU Manual," and with the Back-Cover Texts as in (a) below. (a) The FSF's Back-Cover Text is: "You are free to copy and modify this GNU Manual. Buying copies from GNU Press supports the FSF in developing GNU and promoting software freedom."  File: gdb.info, Node: Bytecode Descriptions, Next: Using Agent Expressions, Prev: General Bytecode Design, Up: Agent Expressions E.2 Bytecode Descriptions ========================= Each bytecode description has the following form: `add' (0x02): A B => A+B Pop the top two stack items, A and B, as integers; push their sum, as an integer. In this example, `add' is the name of the bytecode, and `(0x02)' is the one-byte value used to encode the bytecode, in hexadecimal. The phrase "A B => A+B" shows the stack before and after the bytecode executes. Beforehand, the stack must contain at least two values, A and B; since the top of the stack is to the right, B is on the top of the stack, and A is underneath it. After execution, the bytecode will have popped A and B from the stack, and replaced them with a single value, A+B. There may be other values on the stack below those shown, but the bytecode affects only those shown. Here is another example: `const8' (0x22) N: => N Push the 8-bit integer constant N on the stack, without sign extension. In this example, the bytecode `const8' takes an operand N directly from the bytecode stream; the operand follows the `const8' bytecode itself. We write any such operands immediately after the name of the bytecode, before the colon, and describe the exact encoding of the operand in the bytecode stream in the body of the bytecode description. For the `const8' bytecode, there are no stack items given before the =>; this simply means that the bytecode consumes no values from the stack. If a bytecode consumes no values, or produces no values, the list on either side of the => may be empty. If a value is written as A, B, or N, then the bytecode treats it as an integer. If a value is written is ADDR, then the bytecode treats it as an address. We do not fully describe the floating point operations here; although this design can be extended in a clean way to handle floating point values, they are not of immediate interest to the customer, so we avoid describing them, to save time. `float' (0x01): => Prefix for floating-point bytecodes. Not implemented yet. `add' (0x02): A B => A+B Pop two integers from the stack, and push their sum, as an integer. `sub' (0x03): A B => A-B Pop two integers from the stack, subtract the top value from the next-to-top value, and push the difference. `mul' (0x04): A B => A*B Pop two integers from the stack, multiply them, and push the product on the stack. Note that, when one multiplies two N-bit numbers yielding another N-bit number, it is irrelevant whether the numbers are signed or not; the results are the same. `div_signed' (0x05): A B => A/B Pop two signed integers from the stack; divide the next-to-top value by the top value, and push the quotient. If the divisor is zero, terminate with an error. `div_unsigned' (0x06): A B => A/B Pop two unsigned integers from the stack; divide the next-to-top value by the top value, and push the quotient. If the divisor is zero, terminate with an error. `rem_signed' (0x07): A B => A MODULO B Pop two signed integers from the stack; divide the next-to-top value by the top value, and push the remainder. If the divisor is zero, terminate with an error. `rem_unsigned' (0x08): A B => A MODULO B Pop two unsigned integers from the stack; divide the next-to-top value by the top value, and push the remainder. If the divisor is zero, terminate with an error. `lsh' (0x09): A B => A< `(signed)'A>>B Pop two integers from the stack; let A be the next-to-top value, and B be the top value. Shift A right by B bits, inserting copies of the top bit at the high end, and push the result. `rsh_unsigned' (0x0b): A B => A>>B Pop two integers from the stack; let A be the next-to-top value, and B be the top value. Shift A right by B bits, inserting zero bits at the high end, and push the result. `log_not' (0x0e): A => !A Pop an integer from the stack; if it is zero, push the value one; otherwise, push the value zero. `bit_and' (0x0f): A B => A&B Pop two integers from the stack, and push their bitwise `and'. `bit_or' (0x10): A B => A|B Pop two integers from the stack, and push their bitwise `or'. `bit_xor' (0x11): A B => A^B Pop two integers from the stack, and push their bitwise exclusive-`or'. `bit_not' (0x12): A => ~A Pop an integer from the stack, and push its bitwise complement. `equal' (0x13): A B => A=B Pop two integers from the stack; if they are equal, push the value one; otherwise, push the value zero. `less_signed' (0x14): A B => A A A, sign-extended from N bits Pop an unsigned value from the stack; treating it as an N-bit twos-complement value, extend it to full length. This means that all bits to the left of bit N-1 (where the least significant bit is bit 0) are set to the value of bit N-1. Note that N may be larger than or equal to the width of the stack elements of the bytecode engine; in this case, the bytecode should have no effect. The number of source bits to preserve, N, is encoded as a single byte unsigned integer following the `ext' bytecode. `zero_ext' (0x2a) N: A => A, zero-extended from N bits Pop an unsigned value from the stack; zero all but the bottom N bits. This means that all bits to the left of bit N-1 (where the least significant bit is bit 0) are set to the value of bit N-1. The number of source bits to preserve, N, is encoded as a single byte unsigned integer following the `zero_ext' bytecode. `ref8' (0x17): ADDR => A `ref16' (0x18): ADDR => A `ref32' (0x19): ADDR => A `ref64' (0x1a): ADDR => A Pop an address ADDR from the stack. For bytecode `ref'N, fetch an N-bit value from ADDR, using the natural target endianness. Push the fetched value as an unsigned integer. Note that ADDR may not be aligned in any particular way; the `refN' bytecodes should operate correctly for any address. If attempting to access memory at ADDR would cause a processor exception of some sort, terminate with an error. `ref_float' (0x1b): ADDR => D `ref_double' (0x1c): ADDR => D `ref_long_double' (0x1d): ADDR => D `l_to_d' (0x1e): A => D `d_to_l' (0x1f): D => A Not implemented yet. `dup' (0x28): A => A A Push another copy of the stack's top element. `swap' (0x2b): A B => B A Exchange the top two items on the stack. `pop' (0x29): A => Discard the top value on the stack. `if_goto' (0x20) OFFSET: A => Pop an integer off the stack; if it is non-zero, branch to the given offset in the bytecode string. Otherwise, continue to the next instruction in the bytecode stream. In other words, if A is non-zero, set the `pc' register to `start' + OFFSET. Thus, an offset of zero denotes the beginning of the expression. The OFFSET is stored as a sixteen-bit unsigned value, stored immediately following the `if_goto' bytecode. It is always stored most significant byte first, regardless of the target's normal endianness. The offset is not guaranteed to fall at any particular alignment within the bytecode stream; thus, on machines where fetching a 16-bit on an unaligned address raises an exception, you should fetch the offset one byte at a time. `goto' (0x21) OFFSET: => Branch unconditionally to OFFSET; in other words, set the `pc' register to `start' + OFFSET. The offset is stored in the same way as for the `if_goto' bytecode. `const8' (0x22) N: => N `const16' (0x23) N: => N `const32' (0x24) N: => N `const64' (0x25) N: => N Push the integer constant N on the stack, without sign extension. To produce a small negative value, push a small twos-complement value, and then sign-extend it using the `ext' bytecode. The constant N is stored in the appropriate number of bytes following the `const'B bytecode. The constant N is always stored most significant byte first, regardless of the target's normal endianness. The constant is not guaranteed to fall at any particular alignment within the bytecode stream; thus, on machines where fetching a 16-bit on an unaligned address raises an exception, you should fetch N one byte at a time. `reg' (0x26) N: => A Push the value of register number N, without sign extension. The registers are numbered following GDB's conventions. The register number N is encoded as a 16-bit unsigned integer immediately following the `reg' bytecode. It is always stored most significant byte first, regardless of the target's normal endianness. The register number is not guaranteed to fall at any particular alignment within the bytecode stream; thus, on machines where fetching a 16-bit on an unaligned address raises an exception, you should fetch the register number one byte at a time. `getv' (0x2c) N: => V Push the value of trace state variable number N, without sign extension. The variable number N is encoded as a 16-bit unsigned integer immediately following the `getv' bytecode. It is always stored most significant byte first, regardless of the target's normal endianness. The variable number is not guaranteed to fall at any particular alignment within the bytecode stream; thus, on machines where fetching a 16-bit on an unaligned address raises an exception, you should fetch the register number one byte at a time. `setv' (0x2d) N: => V Set trace state variable number N to the value found on the top of the stack. The stack is unchanged, so that the value is readily available if the assignment is part of a larger expression. The handling of N is as described for `getv'. `trace' (0x0c): ADDR SIZE => Record the contents of the SIZE bytes at ADDR in a trace buffer, for later retrieval by GDB. `trace_quick' (0x0d) SIZE: ADDR => ADDR Record the contents of the SIZE bytes at ADDR in a trace buffer, for later retrieval by GDB. SIZE is a single byte unsigned integer following the `trace' opcode. This bytecode is equivalent to the sequence `dup const8 SIZE trace', but we provide it anyway to save space in bytecode strings. `trace16' (0x30) SIZE: ADDR => ADDR Identical to trace_quick, except that SIZE is a 16-bit big-endian unsigned integer, not a single byte. This should probably have been named `trace_quick16', for consistency. `tracev' (0x2e) N: => A Record the value of trace state variable number N in the trace buffer. The handling of N is as described for `getv'. `end' (0x27): => Stop executing bytecode; the result should be the top element of the stack. If the purpose of the expression was to compute an lvalue or a range of memory, then the next-to-top of the stack is the lvalue's address, and the top of the stack is the lvalue's size, in bytes.  File: gdb.info, Node: Using Agent Expressions, Next: Varying Target Capabilities, Prev: Bytecode Descriptions, Up: Agent Expressions E.3 Using Agent Expressions =========================== Agent expressions can be used in several different ways by GDB, and the debugger can generate different bytecode sequences as appropriate. One possibility is to do expression evaluation on the target rather than the host, such as for the conditional of a conditional tracepoint. In such a case, GDB compiles the source expression into a bytecode sequence that simply gets values from registers or memory, does arithmetic, and returns a result. Another way to use agent expressions is for tracepoint data collection. GDB generates a different bytecode sequence for collection; in addition to bytecodes that do the calculation, GDB adds `trace' bytecodes to save the pieces of memory that were used. * The user selects trace points in the program's code at which GDB should collect data. * The user specifies expressions to evaluate at each trace point. These expressions may denote objects in memory, in which case those objects' contents are recorded as the program runs, or computed values, in which case the values themselves are recorded. * GDB transmits the tracepoints and their associated expressions to the GDB agent, running on the debugging target. * The agent arranges to be notified when a trace point is hit. * When execution on the target reaches a trace point, the agent evaluates the expressions associated with that trace point, and records the resulting values and memory ranges. * Later, when the user selects a given trace event and inspects the objects and expression values recorded, GDB talks to the agent to retrieve recorded data as necessary to meet the user's requests. If the user asks to see an object whose contents have not been recorded, GDB reports an error.  File: gdb.info, Node: Varying Target Capabilities, Next: Rationale, Prev: Using Agent Expressions, Up: Agent Expressions E.4 Varying Target Capabilities =============================== Some targets don't support floating-point, and some would rather not have to deal with `long long' operations. Also, different targets will have different stack sizes, and different bytecode buffer lengths. Thus, GDB needs a way to ask the target about itself. We haven't worked out the details yet, but in general, GDB should be able to send the target a packet asking it to describe itself. The reply should be a packet whose length is explicit, so we can add new information to the packet in future revisions of the agent, without confusing old versions of GDB, and it should contain a version number. It should contain at least the following information: * whether floating point is supported * whether `long long' is supported * maximum acceptable size of bytecode stack * maximum acceptable length of bytecode expressions * which registers are actually available for collection * whether the target supports disabled tracepoints  File: gdb.info, Node: Rationale, Prev: Varying Target Capabilities, Up: Agent Expressions E.5 Rationale ============= Some of the design decisions apparent above are arguable. What about stack overflow/underflow? GDB should be able to query the target to discover its stack size. Given that information, GDB can determine at translation time whether a given expression will overflow the stack. But this spec isn't about what kinds of error-checking GDB ought to do. Why are you doing everything in LONGEST? Speed isn't important, but agent code size is; using LONGEST brings in a bunch of support code to do things like division, etc. So this is a serious concern. First, note that you don't need different bytecodes for different operand sizes. You can generate code without _knowing_ how big the stack elements actually are on the target. If the target only supports 32-bit ints, and you don't send any 64-bit bytecodes, everything just works. The observation here is that the MIPS and the Alpha have only fixed-size registers, and you can still get C's semantics even though most instructions only operate on full-sized words. You just need to make sure everything is properly sign-extended at the right times. So there is no need for 32- and 64-bit variants of the bytecodes. Just implement everything using the largest size you support. GDB should certainly check to see what sizes the target supports, so the user can get an error earlier, rather than later. But this information is not necessary for correctness. Why don't you have `>' or `<=' operators? I want to keep the interpreter small, and we don't need them. We can combine the `less_' opcodes with `log_not', and swap the order of the operands, yielding all four asymmetrical comparison operators. For example, `(x <= y)' is `! (x > y)', which is `! (y < x)'. Why do you have `log_not'? Why do you have `ext'? Why do you have `zero_ext'? These are all easily synthesized from other instructions, but I expect them to be used frequently, and they're simple, so I include them to keep bytecode strings short. `log_not' is equivalent to `const8 0 equal'; it's used in half the relational operators. `ext N' is equivalent to `const8 S-N lsh const8 S-N rsh_signed', where S is the size of the stack elements; it follows `refM' and REG bytecodes when the value should be signed. See the next bulleted item. `zero_ext N' is equivalent to `constM MASK log_and'; it's used whenever we push the value of a register, because we can't assume the upper bits of the register aren't garbage. Why not have sign-extending variants of the `ref' operators? Because that would double the number of `ref' operators, and we need the `ext' bytecode anyway for accessing bitfields. Why not have constant-address variants of the `ref' operators? Because that would double the number of `ref' operators again, and `const32 ADDRESS ref32' is only one byte longer. Why do the `refN' operators have to support unaligned fetches? GDB will generate bytecode that fetches multi-byte values at unaligned addresses whenever the executable's debugging information tells it to. Furthermore, GDB does not know the value the pointer will have when GDB generates the bytecode, so it cannot determine whether a particular fetch will be aligned or not. In particular, structure bitfields may be several bytes long, but follow no alignment rules; members of packed structures are not necessarily aligned either. In general, there are many cases where unaligned references occur in correct C code, either at the programmer's explicit request, or at the compiler's discretion. Thus, it is simpler to make the GDB agent bytecodes work correctly in all circumstances than to make GDB guess in each case whether the compiler did the usual thing. Why are there no side-effecting operators? Because our current client doesn't want them? That's a cheap answer. I think the real answer is that I'm afraid of implementing function calls. We should re-visit this issue after the present contract is delivered. Why aren't the `goto' ops PC-relative? The interpreter has the base address around anyway for PC bounds checking, and it seemed simpler. Why is there only one offset size for the `goto' ops? Offsets are currently sixteen bits. I'm not happy with this situation either: Suppose we have multiple branch ops with different offset sizes. As I generate code left-to-right, all my jumps are forward jumps (there are no loops in expressions), so I never know the target when I emit the jump opcode. Thus, I have to either always assume the largest offset size, or do jump relaxation on the code after I generate it, which seems like a big waste of time. I can imagine a reasonable expression being longer than 256 bytes. I can't imagine one being longer than 64k. Thus, we need 16-bit offsets. This kind of reasoning is so bogus, but relaxation is pathetic. The other approach would be to generate code right-to-left. Then I'd always know my offset size. That might be fun. Where is the function call bytecode? When we add side-effects, we should add this. Why does the `reg' bytecode take a 16-bit register number? Intel's IA-64 architecture has 128 general-purpose registers, and 128 floating-point registers, and I'm sure it has some random control registers. Why do we need `trace' and `trace_quick'? Because GDB needs to record all the memory contents and registers an expression touches. If the user wants to evaluate an expression `x->y->z', the agent must record the values of `x' and `x->y' as well as the value of `x->y->z'. Don't the `trace' bytecodes make the interpreter less general? They do mean that the interpreter contains special-purpose code, but that doesn't mean the interpreter can only be used for that purpose. If an expression doesn't use the `trace' bytecodes, they don't get in its way. Why doesn't `trace_quick' consume its arguments the way everything else does? In general, you do want your operators to consume their arguments; it's consistent, and generally reduces the amount of stack rearrangement necessary. However, `trace_quick' is a kludge to save space; it only exists so we needn't write `dup const8 SIZE trace' before every memory reference. Therefore, it's okay for it not to consume its arguments; it's meant for a specific context in which we know exactly what it should do with the stack. If we're going to have a kludge, it should be an effective kludge. Why does `trace16' exist? That opcode was added by the customer that contracted Cygnus for the data tracing work. I personally think it is unnecessary; objects that large will be quite rare, so it is okay to use `dup const16 SIZE trace' in those cases. Whatever we decide to do with `trace16', we should at least leave opcode 0x30 reserved, to remain compatible with the customer who added it.  File: gdb.info, Node: Trace File Format, Next: Copying, Prev: Operating System Information, Up: Top Appendix F Trace File Format **************************** The trace file comes in three parts: a header, a textual description section, and a trace frame section with binary data. The header has the form `\x7fTRACE0\n'. The first byte is `0x7f' so as to indicate that the file contains binary data, while the `0' is a version number that may have different values in the future. The description section consists of multiple lines of ASCII text separated by newline characters (`0xa'). The lines may include a variety of optional descriptive or context-setting information, such as tracepoint definitions or register set size. GDB will ignore any line that it does not recognize. An empty line marks the end of this section. The trace frame section consists of a number of consecutive frames. Each frame begins with a two-byte tracepoint number, followed by a four-byte size giving the amount of data in the frame. The data in the frame consists of a number of blocks, each introduced by a character indicating its type (at least register, memory, and trace state variable). The data in this section is raw binary, not a hexadecimal or other encoding; its endianness matches the target's endianness. `R BYTES' Register block. The number and ordering of bytes matches that of a `g' packet in the remote protocol. Note that these are the actual bytes, in target order and GDB register order, not a hexadecimal encoding. `M ADDRESS LENGTH BYTES...' Memory block. This is a contiguous block of memory, at the 8-byte address ADDRESS, with a 2-byte length LENGTH, followed by LENGTH bytes. `V NUMBER VALUE' Trace state variable block. This records the 8-byte signed value VALUE of trace state variable numbered NUMBER. Future enhancements of the trace file format may include additional types of blocks.  File: gdb.info, Node: Target Descriptions, Next: Operating System Information, Prev: Agent Expressions, Up: Top Appendix G Target Descriptions ****************************** *Warning:* target descriptions are still under active development, and the contents and format may change between GDB releases. The format is expected to stabilize in the future. One of the challenges of using GDB to debug embedded systems is that there are so many minor variants of each processor architecture in use. It is common practice for vendors to start with a standard processor core -- ARM, PowerPC, or MIPS, for example -- and then make changes to adapt it to a particular market niche. Some architectures have hundreds of variants, available from dozens of vendors. This leads to a number of problems: * With so many different customized processors, it is difficult for the GDB maintainers to keep up with the changes. * Since individual variants may have short lifetimes or limited audiences, it may not be worthwhile to carry information about every variant in the GDB source tree. * When GDB does support the architecture of the embedded system at hand, the task of finding the correct architecture name to give the `set architecture' command can be error-prone. To address these problems, the GDB remote protocol allows a target system to not only identify itself to GDB, but to actually describe its own features. This lets GDB support processor variants it has never seen before -- to the extent that the descriptions are accurate, and that GDB understands them. GDB must be linked with the Expat library to support XML target descriptions. *Note Expat::. * Menu: * Retrieving Descriptions:: How descriptions are fetched from a target. * Target Description Format:: The contents of a target description. * Predefined Target Types:: Standard types available for target descriptions. * Standard Target Features:: Features GDB knows about.  File: gdb.info, Node: Retrieving Descriptions, Next: Target Description Format, Up: Target Descriptions G.1 Retrieving Descriptions =========================== Target descriptions can be read from the target automatically, or specified by the user manually. The default behavior is to read the description from the target. GDB retrieves it via the remote protocol using `qXfer' requests (*note qXfer: General Query Packets.). The ANNEX in the `qXfer' packet will be `target.xml'. The contents of the `target.xml' annex are an XML document, of the form described in *Note Target Description Format::. Alternatively, you can specify a file to read for the target description. If a file is set, the target will not be queried. The commands to specify a file are: `set tdesc filename PATH' Read the target description from PATH. `unset tdesc filename' Do not read the XML target description from a file. GDB will use the description supplied by the current target. `show tdesc filename' Show the filename to read for a target description, if any.  File: gdb.info, Node: Target Description Format, Next: Predefined Target Types, Prev: Retrieving Descriptions, Up: Target Descriptions G.2 Target Description Format ============================= A target description annex is an XML (http://www.w3.org/XML/) document which complies with the Document Type Definition provided in the GDB sources in `gdb/features/gdb-target.dtd'. This means you can use generally available tools like `xmllint' to check that your feature descriptions are well-formed and valid. However, to help people unfamiliar with XML write descriptions for their targets, we also describe the grammar here. Target descriptions can identify the architecture of the remote target and (for some architectures) provide information about custom register sets. They can also identify the OS ABI of the remote target. GDB can use this information to autoconfigure for your target, or to warn you if you connect to an unsupported target. Here is a simple target description: i386:x86-64 This minimal description only says that the target uses the x86-64 architecture. A target description has the following overall form, with [ ] marking optional elements and ... marking repeatable elements. The elements are explained further below. [ARCHITECTURE] [OSABI] [COMPATIBLE] [FEATURE...] The description is generally insensitive to whitespace and line breaks, under the usual common-sense rules. The XML version declaration and document type declaration can generally be omitted (GDB does not require them), but specifying them may be useful for XML validation tools. The `version' attribute for `' may also be omitted, but we recommend including it; if future versions of GDB use an incompatible revision of `gdb-target.dtd', they will detect and report the version mismatch. G.2.1 Inclusion --------------- It can sometimes be valuable to split a target description up into several different annexes, either for organizational purposes, or to share files between different possible target descriptions. You can divide a description into multiple files by replacing any element of the target description with an inclusion directive of the form: When GDB encounters an element of this form, it will retrieve the named XML DOCUMENT, and replace the inclusion directive with the contents of that document. If the current description was read using `qXfer', then so will be the included document; DOCUMENT will be interpreted as the name of an annex. If the current description was read from a file, GDB will look for DOCUMENT as a file in the same directory where it found the original description. G.2.2 Architecture ------------------ An `' element has this form: ARCH ARCH is one of the architectures from the set accepted by `set architecture' (*note Specifying a Debugging Target: Targets.). G.2.3 OS ABI ------------ This optional field was introduced in GDB version 7.0. Previous versions of GDB ignore it. An `' element has this form: ABI-NAME ABI-NAME is an OS ABI name from the same selection accepted by `set osabi' (*note Configuring the Current ABI: ABI.). G.2.4 Compatible Architecture ----------------------------- This optional field was introduced in GDB version 7.0. Previous versions of GDB ignore it. A `' element has this form: ARCH ARCH is one of the architectures from the set accepted by `set architecture' (*note Specifying a Debugging Target: Targets.). A `' element is used to specify that the target is able to run binaries in some other than the main target architecture given by the `' element. For example, on the Cell Broadband Engine, the main architecture is `powerpc:common' or `powerpc:common64', but the system is able to run binaries in the `spu' architecture as well. The way to describe this capability with `' is as follows: powerpc:common spu G.2.5 Features -------------- Each `' describes some logical portion of the target system. Features are currently used to describe available CPU registers and the types of their contents. A `' element has this form: [TYPE...] REG... Each feature's name should be unique within the description. The name of a feature does not matter unless GDB has some special knowledge of the contents of that feature; if it does, the feature should have its standard name. *Note Standard Target Features::. G.2.6 Types ----------- Any register's value is a collection of bits which GDB must interpret. The default interpretation is a two's complement integer, but other types can be requested by name in the register description. Some predefined types are provided by GDB (*note Predefined Target Types::), and the description can define additional composite types. Each type element must have an `id' attribute, which gives a unique (within the containing `') name to the type. Types must be defined before they are used. Some targets offer vector registers, which can be treated as arrays of scalar elements. These types are written as `' elements, specifying the array element type, TYPE, and the number of elements, COUNT: If a register's value is usefully viewed in multiple ways, define it with a union type containing the useful representations. The `' element contains one or more `' elements, each of which has a NAME and a TYPE: ... If a register's value is composed from several separate values, define it with a structure type. There are two forms of the `' element; a `' element must either contain only bitfields or contain no bitfields. If the structure contains only bitfields, its total size in bytes must be specified, each bitfield must have an explicit start and end, and bitfields are automatically assigned an integer type. The field's START should be less than or equal to its END, and zero represents the least significant bit. ... If the structure contains no bitfields, then each field has an explicit type, and no implicit padding is added. ... If a register's value is a series of single-bit flags, define it with a flags type. The `' element has an explicit SIZE and contains one or more `' elements. Each field has a NAME, a START, and an END. Only single-bit flags are supported. ... G.2.7 Registers --------------- Each register is represented as an element with this form: The components are as follows: NAME The register's name; it must be unique within the target description. BITSIZE The register's size, in bits. REGNUM The register's number. If omitted, a register's number is one greater than that of the previous register (either in the current feature or in a preceeding feature); the first register in the target description defaults to zero. This register number is used to read or write the register; e.g. it is used in the remote `p' and `P' packets, and registers appear in the `g' and `G' packets in order of increasing register number. SAVE-RESTORE Whether the register should be preserved across inferior function calls; this must be either `yes' or `no'. The default is `yes', which is appropriate for most registers except for some system control registers; this is not related to the target's ABI. TYPE The type of the register. TYPE may be a predefined type, a type defined in the current feature, or one of the special types `int' and `float'. `int' is an integer type of the correct size for BITSIZE, and `float' is a floating point type (in the architecture's normal floating point format) of the correct size for BITSIZE. The default is `int'. GROUP The register group to which this register belongs. GROUP must be either `general', `float', or `vector'. If no GROUP is specified, GDB will not display the register in `info registers'.  File: gdb.info, Node: Predefined Target Types, Next: Standard Target Features, Prev: Target Description Format, Up: Target Descriptions G.3 Predefined Target Types =========================== Type definitions in the self-description can build up composite types from basic building blocks, but can not define fundamental types. Instead, standard identifiers are provided by GDB for the fundamental types. The currently supported types are: `int8' `int16' `int32' `int64' `int128' Signed integer types holding the specified number of bits. `uint8' `uint16' `uint32' `uint64' `uint128' Unsigned integer types holding the specified number of bits. `code_ptr' `data_ptr' Pointers to unspecified code and data. The program counter and any dedicated return address register may be marked as code pointers; printing a code pointer converts it into a symbolic address. The stack pointer and any dedicated address registers may be marked as data pointers. `ieee_single' Single precision IEEE floating point. `ieee_double' Double precision IEEE floating point. `arm_fpa_ext' The 12-byte extended precision format used by ARM FPA registers. `i387_ext' The 10-byte extended precision format used by x87 registers. `i386_eflags' 32bit EFLAGS register used by x86. `i386_mxcsr' 32bit MXCSR register used by x86.  File: gdb.info, Node: Standard Target Features, Prev: Predefined Target Types, Up: Target Descriptions G.4 Standard Target Features ============================ A target description must contain either no registers or all the target's registers. If the description contains no registers, then GDB will assume a default register layout, selected based on the architecture. If the description contains any registers, the default layout will not be used; the standard registers must be described in the target description, in such a way that GDB can recognize them. This is accomplished by giving specific names to feature elements which contain standard registers. GDB will look for features with those names and verify that they contain the expected registers; if any known feature is missing required registers, or if any required feature is missing, GDB will reject the target description. You can add additional registers to any of the standard features -- GDB will display them just as if they were added to an unrecognized feature. This section lists the known features and their expected contents. Sample XML documents for these features are included in the GDB source tree, in the directory `gdb/features'. Names recognized by GDB should include the name of the company or organization which selected the name, and the overall architecture to which the feature applies; so e.g. the feature containing ARM core registers is named `org.gnu.gdb.arm.core'. The names of registers are not case sensitive for the purpose of recognizing standard features, but GDB will only display registers using the capitalization used in the description. * Menu: * ARM Features:: * i386 Features:: * MIPS Features:: * M68K Features:: * PowerPC Features::  File: gdb.info, Node: ARM Features, Next: i386 Features, Up: Standard Target Features G.4.1 ARM Features ------------------ The `org.gnu.gdb.arm.core' feature is required for ARM targets. It should contain registers `r0' through `r13', `sp', `lr', `pc', and `cpsr'. The `org.gnu.gdb.arm.fpa' feature is optional. If present, it should contain registers `f0' through `f7' and `fps'. The `org.gnu.gdb.xscale.iwmmxt' feature is optional. If present, it should contain at least registers `wR0' through `wR15' and `wCGR0' through `wCGR3'. The `wCID', `wCon', `wCSSF', and `wCASF' registers are optional. The `org.gnu.gdb.arm.vfp' feature is optional. If present, it should contain at least registers `d0' through `d15'. If they are present, `d16' through `d31' should also be included. GDB will synthesize the single-precision registers from halves of the double-precision registers. The `org.gnu.gdb.arm.neon' feature is optional. It does not need to contain registers; it instructs GDB to display the VFP double-precision registers as vectors and to synthesize the quad-precision registers from pairs of double-precision registers. If this feature is present, `org.gnu.gdb.arm.vfp' must also be present and include 32 double-precision registers.  File: gdb.info, Node: i386 Features, Next: MIPS Features, Prev: ARM Features, Up: Standard Target Features G.4.2 i386 Features ------------------- The `org.gnu.gdb.i386.core' feature is required for i386/amd64 targets. It should describe the following registers: - `eax' through `edi' plus `eip' for i386 - `rax' through `r15' plus `rip' for amd64 - `eflags', `cs', `ss', `ds', `es', `fs', `gs' - `st0' through `st7' - `fctrl', `fstat', `ftag', `fiseg', `fioff', `foseg', `fooff' and `fop' The register sets may be different, depending on the target. The `org.gnu.gdb.i386.sse' feature is optional. It should describe registers: - `xmm0' through `xmm7' for i386 - `xmm0' through `xmm15' for amd64 - `mxcsr' The `org.gnu.gdb.i386.avx' feature is optional and requires the `org.gnu.gdb.i386.sse' feature. It should describe the upper 128 bits of YMM registers: - `ymm0h' through `ymm7h' for i386 - `ymm0h' through `ymm15h' for amd64 - The `org.gnu.gdb.i386.linux' feature is optional. It should describe a single register, `orig_eax'.  File: gdb.info, Node: MIPS Features, Next: M68K Features, Prev: i386 Features, Up: Standard Target Features G.4.3 MIPS Features ------------------- The `org.gnu.gdb.mips.cpu' feature is required for MIPS targets. It should contain registers `r0' through `r31', `lo', `hi', and `pc'. They may be 32-bit or 64-bit depending on the target. The `org.gnu.gdb.mips.cp0' feature is also required. It should contain at least the `status', `badvaddr', and `cause' registers. They may be 32-bit or 64-bit depending on the target. The `org.gnu.gdb.mips.fpu' feature is currently required, though it may be optional in a future version of GDB. It should contain registers `f0' through `f31', `fcsr', and `fir'. They may be 32-bit or 64-bit depending on the target. The `org.gnu.gdb.mips.linux' feature is optional. It should contain a single register, `restart', which is used by the Linux kernel to control restartable syscalls.  File: gdb.info, Node: M68K Features, Next: PowerPC Features, Prev: MIPS Features, Up: Standard Target Features G.4.4 M68K Features ------------------- ``org.gnu.gdb.m68k.core'' ``org.gnu.gdb.coldfire.core'' ``org.gnu.gdb.fido.core'' One of those features must be always present. The feature that is present determines which flavor of m68k is used. The feature that is present should contain registers `d0' through `d7', `a0' through `a5', `fp', `sp', `ps' and `pc'. ``org.gnu.gdb.coldfire.fp'' This feature is optional. If present, it should contain registers `fp0' through `fp7', `fpcontrol', `fpstatus' and `fpiaddr'.  File: gdb.info, Node: PowerPC Features, Prev: M68K Features, Up: Standard Target Features G.4.5 PowerPC Features ---------------------- The `org.gnu.gdb.power.core' feature is required for PowerPC targets. It should contain registers `r0' through `r31', `pc', `msr', `cr', `lr', `ctr', and `xer'. They may be 32-bit or 64-bit depending on the target. The `org.gnu.gdb.power.fpu' feature is optional. It should contain registers `f0' through `f31' and `fpscr'. The `org.gnu.gdb.power.altivec' feature is optional. It should contain registers `vr0' through `vr31', `vscr', and `vrsave'. The `org.gnu.gdb.power.vsx' feature is optional. It should contain registers `vs0h' through `vs31h'. GDB will combine these registers with the floating point registers (`f0' through `f31') and the altivec registers (`vr0' through `vr31') to present the 128-bit wide registers `vs0' through `vs63', the set of vector registers for POWER7. The `org.gnu.gdb.power.spe' feature is optional. It should contain registers `ev0h' through `ev31h', `acc', and `spefscr'. SPE targets should provide 32-bit registers in `org.gnu.gdb.power.core' and provide the upper halves in `ev0h' through `ev31h'. GDB will combine these to present registers `ev0' through `ev31' to the user.  File: gdb.info, Node: Operating System Information, Next: Trace File Format, Prev: Target Descriptions, Up: Top Appendix H Operating System Information *************************************** * Menu: * Process list:: Users of GDB often wish to obtain information about the state of the operating system running on the target--for example the list of processes, or the list of open files. This section describes the mechanism that makes it possible. This mechanism is similar to the target features mechanism (*note Target Descriptions::), but focuses on a different aspect of target. Operating system information is retrived from the target via the remote protocol, using `qXfer' requests (*note qXfer osdata read::). The object name in the request should be `osdata', and the ANNEX identifies the data to be fetched.  File: gdb.info, Node: Process list, Up: Operating System Information H.1 Process list ================ When requesting the process list, the ANNEX field in the `qXfer' request should be `processes'. The returned data is an XML document. The formal syntax of this document is defined in `gdb/features/osdata.dtd'. An example document is: 1 root /sbin/init 1,2,3 Each item should include a column whose name is `pid'. The value of that column should identify the process on the target. The `user' and `command' columns are optional, and will be displayed by GDB. The `cores' column, if present, should contain a comma-separated list of cores that this process is running on. Target may provide additional columns, which GDB currently ignores.  File: gdb.info, Node: Copying, Next: GNU Free Documentation License, Prev: Trace File Format, Up: Top Appendix I GNU GENERAL PUBLIC LICENSE ************************************* Version 3, 29 June 2007 Copyright (C) 2007 Free Software Foundation, Inc. `http://fsf.org/' Everyone is permitted to copy and distribute verbatim copies of this license document, but changing it is not allowed. Preamble ======== The GNU General Public License is a free, copyleft license for software and other kinds of works. The licenses for most software and other practical works are designed to take away your freedom to share and change the works. By contrast, the GNU General Public License is intended to guarantee your freedom to share and change all versions of a program--to make sure it remains free software for all its users. We, the Free Software Foundation, use the GNU General Public License for most of our software; it applies also to any other work released this way by its authors. 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If, pursuant to or in connection with a single transaction or arrangement, you convey, or propagate by procuring conveyance of, a covered work, and grant a patent license to some of the parties receiving the covered work authorizing them to use, propagate, modify or convey a specific copy of the covered work, then the patent license you grant is automatically extended to all recipients of the covered work and works based on it. A patent license is "discriminatory" if it does not include within the scope of its coverage, prohibits the exercise of, or is conditioned on the non-exercise of one or more of the rights that are specifically granted under this License. You may not convey a covered work if you are a party to an arrangement with a third party that is in the business of distributing software, under which you make payment to the third party based on the extent of your activity of conveying the work, and under which the third party grants, to any of the parties who would receive the covered work from you, a discriminatory patent license (a) in connection with copies of the covered work conveyed by you (or copies made from those copies), or (b) primarily for and in connection with specific products or compilations that contain the covered work, unless you entered into that arrangement, or that patent license was granted, prior to 28 March 2007. Nothing in this License shall be construed as excluding or limiting any implied license or other defenses to infringement that may otherwise be available to you under applicable patent law. 12. No Surrender of Others' Freedom. If conditions are imposed on you (whether by court order, agreement or otherwise) that contradict the conditions of this License, they do not excuse you from the conditions of this License. If you cannot convey a covered work so as to satisfy simultaneously your obligations under this License and any other pertinent obligations, then as a consequence you may not convey it at all. For example, if you agree to terms that obligate you to collect a royalty for further conveying from those to whom you convey the Program, the only way you could satisfy both those terms and this License would be to refrain entirely from conveying the Program. 13. Use with the GNU Affero General Public License. Notwithstanding any other provision of this License, you have permission to link or combine any covered work with a work licensed under version 3 of the GNU Affero General Public License into a single combined work, and to convey the resulting work. The terms of this License will continue to apply to the part which is the covered work, but the special requirements of the GNU Affero General Public License, section 13, concerning interaction through a network will apply to the combination as such. 14. Revised Versions of this License. The Free Software Foundation may publish revised and/or new versions of the GNU General Public 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. Each version is given a distinguishing version number. If the Program specifies that a certain numbered version of the GNU General Public License "or any later version" applies to it, you have the option of following the terms and conditions either of that numbered version or of any later version published by the Free Software Foundation. If the Program does not specify a version number of the GNU General Public License, you may choose any version ever published by the Free Software Foundation. If the Program specifies that a proxy can decide which future versions of the GNU General Public License can be used, that proxy's public statement of acceptance of a version permanently authorizes you to choose that version for the Program. Later license versions may give you additional or different permissions. However, no additional obligations are imposed on any author or copyright holder as a result of your choosing to follow a later version. 15. Disclaimer of Warranty. THERE IS NO WARRANTY FOR THE PROGRAM, TO THE EXTENT PERMITTED BY APPLICABLE LAW. EXCEPT WHEN OTHERWISE STATED IN WRITING THE COPYRIGHT HOLDERS AND/OR OTHER PARTIES PROVIDE THE PROGRAM "AS IS" WITHOUT WARRANTY OF ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. THE ENTIRE RISK AS TO THE QUALITY AND PERFORMANCE OF THE PROGRAM IS WITH YOU. SHOULD THE PROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF ALL NECESSARY SERVICING, REPAIR OR CORRECTION. 16. Limitation of Liability. IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MODIFIES AND/OR CONVEYS THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR DAMAGES, INCLUDING ANY GENERAL, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE USE OR INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT LIMITED TO LOSS OF DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY YOU OR THIRD PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY OTHER PROGRAMS), EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. 17. Interpretation of Sections 15 and 16. If the disclaimer of warranty and limitation of liability provided above cannot be given local legal effect according to their terms, reviewing courts shall apply local law that most closely approximates an absolute waiver of all civil liability in connection with the Program, unless a warranty or assumption of liability accompanies a copy of the Program in return for a fee. END OF TERMS AND CONDITIONS =========================== How to Apply These Terms to Your New Programs ============================================= If you develop a new program, and you want it to be of the greatest possible use to the public, the best way to achieve this is to make it free software which everyone can redistribute and change under these terms. To do so, attach the following notices to the program. It is safest to attach them to the start of each source file to most effectively state the exclusion of warranty; and each file should have at least the "copyright" line and a pointer to where the full notice is found. ONE LINE TO GIVE THE PROGRAM'S NAME AND A BRIEF IDEA OF WHAT IT DOES. Copyright (C) YEAR NAME OF AUTHOR This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see `http://www.gnu.org/licenses/'. Also add information on how to contact you by electronic and paper mail. If the program does terminal interaction, make it output a short notice like this when it starts in an interactive mode: PROGRAM Copyright (C) YEAR NAME OF AUTHOR This program comes with ABSOLUTELY NO WARRANTY; for details type `show w'. This is free software, and you are welcome to redistribute it under certain conditions; type `show c' for details. The hypothetical commands `show w' and `show c' should show the appropriate parts of the General Public License. Of course, your program's commands might be different; for a GUI interface, you would use an "about box". You should also get your employer (if you work as a programmer) or school, if any, to sign a "copyright disclaimer" for the program, if necessary. For more information on this, and how to apply and follow the GNU GPL, see `http://www.gnu.org/licenses/'. The GNU General Public License does not permit incorporating your program into proprietary programs. If your program is a subroutine library, you may consider it more useful to permit linking proprietary applications with the library. If this is what you want to do, use the GNU Lesser General Public License instead of this License. But first, please read `http://www.gnu.org/philosophy/why-not-lgpl.html'.  File: gdb.info, Node: GNU Free Documentation License, Next: Index, Prev: Copying, Up: Top Appendix J GNU Free Documentation License ***************************************** Version 1.3, 3 November 2008 Copyright (C) 2000, 2001, 2002, 2007, 2008 Free Software Foundation, Inc. `http://fsf.org/' Everyone is permitted to copy and distribute verbatim copies of this license document, but changing it is not allowed. 0. PREAMBLE The purpose of this License is to make a manual, textbook, or other functional and useful document "free" in the sense of freedom: to assure everyone the effective freedom to copy and redistribute it, with or without modifying it, either commercially or noncommercially. Secondarily, this License preserves for the author and publisher a way to get credit for their work, while not being considered responsible for modifications made by others. This License is a kind of "copyleft", which means that derivative works of the document must themselves be free in the same sense. It complements the GNU General Public License, which is a copyleft license designed for free software. We have designed this License in order to use it for manuals for free software, because free software needs free documentation: a free program should come with manuals providing the same freedoms that the software does. But this License is not limited to software manuals; it can be used for any textual work, regardless of subject matter or whether it is published as a printed book. We recommend this License principally for works whose purpose is instruction or reference. 1. APPLICABILITY AND DEFINITIONS This License applies to any manual or other work, in any medium, that contains a notice placed by the copyright holder saying it can be distributed under the terms of this License. Such a notice grants a world-wide, royalty-free license, unlimited in duration, to use that work under the conditions stated herein. The "Document", below, refers to any such manual or work. Any member of the public is a licensee, and is addressed as "you". You accept the license if you copy, modify or distribute the work in a way requiring permission under copyright law. A "Modified Version" of the Document means any work containing the Document or a portion of it, either copied verbatim, or with modifications and/or translated into another language. A "Secondary Section" is a named appendix or a front-matter section of the Document that deals exclusively with the relationship of the publishers or authors of the Document to the Document's overall subject (or to related matters) and contains nothing that could fall directly within that overall subject. (Thus, if the Document is in part a textbook of mathematics, a Secondary Section may not explain any mathematics.) The relationship could be a matter of historical connection with the subject or with related matters, or of legal, commercial, philosophical, ethical or political position regarding them. The "Invariant Sections" are certain Secondary Sections whose titles are designated, as being those of Invariant Sections, in the notice that says that the Document is released under this License. If a section does not fit the above definition of Secondary then it is not allowed to be designated as Invariant. The Document may contain zero Invariant Sections. If the Document does not identify any Invariant Sections then there are none. The "Cover Texts" are certain short passages of text that are listed, as Front-Cover Texts or Back-Cover Texts, in the notice that says that the Document is released under this License. A Front-Cover Text may be at most 5 words, and a Back-Cover Text may be at most 25 words. A "Transparent" copy of the Document means a machine-readable copy, represented in a format whose specification is available to the general public, that is suitable for revising the document straightforwardly with generic text editors or (for images composed of pixels) generic paint programs or (for drawings) some widely available drawing editor, and that is suitable for input to text formatters or for automatic translation to a variety of formats suitable for input to text formatters. A copy made in an otherwise Transparent file format whose markup, or absence of markup, has been arranged to thwart or discourage subsequent modification by readers is not Transparent. An image format is not Transparent if used for any substantial amount of text. A copy that is not "Transparent" is called "Opaque". Examples of suitable formats for Transparent copies include plain ASCII without markup, Texinfo input format, LaTeX input format, SGML or XML using a publicly available DTD, and standard-conforming simple HTML, PostScript or PDF designed for human modification. Examples of transparent image formats include PNG, XCF and JPG. Opaque formats include proprietary formats that can be read and edited only by proprietary word processors, SGML or XML for which the DTD and/or processing tools are not generally available, and the machine-generated HTML, PostScript or PDF produced by some word processors for output purposes only. The "Title Page" means, for a printed book, the title page itself, plus such following pages as are needed to hold, legibly, the material this License requires to appear in the title page. For works in formats which do not have any title page as such, "Title Page" means the text near the most prominent appearance of the work's title, preceding the beginning of the body of the text. The "publisher" means any person or entity that distributes copies of the Document to the public. A section "Entitled XYZ" means a named subunit of the Document whose title either is precisely XYZ or contains XYZ in parentheses following text that translates XYZ in another language. (Here XYZ stands for a specific section name mentioned below, such as "Acknowledgements", "Dedications", "Endorsements", or "History".) To "Preserve the Title" of such a section when you modify the Document means that it remains a section "Entitled XYZ" according to this definition. The Document may include Warranty Disclaimers next to the notice which states that this License applies to the Document. These Warranty Disclaimers are considered to be included by reference in this License, but only as regards disclaiming warranties: any other implication that these Warranty Disclaimers may have is void and has no effect on the meaning of this License. 2. VERBATIM COPYING You may copy and distribute the Document in any medium, either commercially or noncommercially, provided that this License, the copyright notices, and the license notice saying this License applies to the Document are reproduced in all copies, and that you add no other conditions whatsoever to those of this License. You may not use technical measures to obstruct or control the reading or further copying of the copies you make or distribute. However, you may accept compensation in exchange for copies. If you distribute a large enough number of copies you must also follow the conditions in section 3. You may also lend copies, under the same conditions stated above, and you may publicly display copies. 3. COPYING IN QUANTITY If you publish printed copies (or copies in media that commonly have printed covers) of the Document, numbering more than 100, and the 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. 4. MODIFICATIONS 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: 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. 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. C. State on the Title page the name of the publisher of the Modified Version, as the publisher. D. Preserve all the copyright notices of the Document. E. Add an appropriate copyright notice for your modifications adjacent to the other copyright notices. 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. G. Preserve in that license notice the full lists of Invariant Sections and required Cover Texts given in the Document's license notice. H. Include an unaltered copy of this License. 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. 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. 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. 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. M. Delete any section Entitled "Endorsements". Such a section may not be included in the Modified Version. N. Do not retitle any existing section to be Entitled "Endorsements" or to conflict in title with any Invariant Section. O. Preserve any Warranty Disclaimers. 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. 5. COMBINING DOCUMENTS 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." 6. COLLECTIONS OF DOCUMENTS 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. 7. AGGREGATION WITH INDEPENDENT WORKS 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. 8. TRANSLATION 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. 9. TERMINATION 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. 10. FUTURE REVISIONS OF THIS LICENSE 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 `http://www.gnu.org/copyleft/'. 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. 11. RELICENSING "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. ADDENDUM: How to use this License for your documents ==================================================== 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: Copyright (C) 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''. If you have Invariant Sections, Front-Cover Texts and Back-Cover Texts, replace the "with...Texts." line with this: with the Invariant Sections being LIST THEIR TITLES, with the Front-Cover Texts being LIST, and with the Back-Cover Texts being LIST. 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.