From 0ca9927a71fed311eea7459b4c85c98cc7ed0352 Mon Sep 17 00:00:00 2001 From: Bill Wendling Date: Thu, 28 Jun 2012 08:43:12 +0000 Subject: Sphinxify the bitcode format document. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@159340 91177308-0d34-0410-b5e6-96231b3b80d8 --- docs/BitCodeFormat.rst | 1045 ++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 1045 insertions(+) create mode 100644 docs/BitCodeFormat.rst (limited to 'docs/BitCodeFormat.rst') diff --git a/docs/BitCodeFormat.rst b/docs/BitCodeFormat.rst new file mode 100644 index 0000000..d3995e7 --- /dev/null +++ b/docs/BitCodeFormat.rst @@ -0,0 +1,1045 @@ +.. _bitcode_format: + +.. role:: raw-html(raw) + :format: html + +======================== +LLVM Bitcode File Format +======================== + +.. contents:: + :local: + +Abstract +======== + +This document describes the LLVM bitstream file format and the encoding of the +LLVM IR into it. + +Overview +======== + +What is commonly known as the LLVM bitcode file format (also, sometimes +anachronistically known as bytecode) is actually two things: a `bitstream +container format`_ and an `encoding of LLVM IR`_ into the container format. + +The bitstream format is an abstract encoding of structured data, very similar to +XML in some ways. Like XML, bitstream files contain tags, and nested +structures, and you can parse the file without having to understand the tags. +Unlike XML, the bitstream format is a binary encoding, and unlike XML it +provides a mechanism for the file to self-describe "abbreviations", which are +effectively size optimizations for the content. + +LLVM IR files may be optionally embedded into a `wrapper`_ structure that makes +it easy to embed extra data along with LLVM IR files. + +This document first describes the LLVM bitstream format, describes the wrapper +format, then describes the record structure used by LLVM IR files. + +.. _bitstream container format: + +Bitstream Format +================ + +The bitstream format is literally a stream of bits, with a very simple +structure. This structure consists of the following concepts: + +* A "`magic number`_" that identifies the contents of the stream. + +* Encoding `primitives`_ like variable bit-rate integers. + +* `Blocks`_, which define nested content. + +* `Data Records`_, which describe entities within the file. + +* Abbreviations, which specify compression optimizations for the file. + +Note that the `llvm-bcanalyzer `_ tool +can be used to dump and inspect arbitrary bitstreams, which is very useful for +understanding the encoding. + +.. _magic number: + +Magic Numbers +------------- + +The first two bytes of a bitcode file are 'BC' (``0x42``, ``0x43``). The second +two bytes are an application-specific magic number. Generic bitcode tools can +look at only the first two bytes to verify the file is bitcode, while +application-specific programs will want to look at all four. + +.. _primitives: + +Primitives +---------- + +A bitstream literally consists of a stream of bits, which are read in order +starting with the least significant bit of each byte. The stream is made up of +a number of primitive values that encode a stream of unsigned integer values. +These integers are encoded in two ways: either as `Fixed Width Integers`_ or as +`Variable Width Integers`_. + +.. _Fixed Width Integers: +.. _fixed-width value: + +Fixed Width Integers +^^^^^^^^^^^^^^^^^^^^ + +Fixed-width integer values have their low bits emitted directly to the file. +For example, a 3-bit integer value encodes 1 as 001. Fixed width integers are +used when there are a well-known number of options for a field. For example, +boolean values are usually encoded with a 1-bit wide integer. + +.. _Variable Width Integers: +.. _Variable Width Integer: +.. _variable-width value: + +Variable Width Integers +^^^^^^^^^^^^^^^^^^^^^^^ + +Variable-width integer (VBR) values encode values of arbitrary size, optimizing +for the case where the values are small. Given a 4-bit VBR field, any 3-bit +value (0 through 7) is encoded directly, with the high bit set to zero. Values +larger than N-1 bits emit their bits in a series of N-1 bit chunks, where all +but the last set the high bit. + +For example, the value 27 (0x1B) is encoded as 1011 0011 when emitted as a vbr4 +value. The first set of four bits indicates the value 3 (011) with a +continuation piece (indicated by a high bit of 1). The next word indicates a +value of 24 (011 << 3) with no continuation. The sum (3+24) yields the value +27. + +.. _char6-encoded value: + +6-bit characters +^^^^^^^^^^^^^^^^ + +6-bit characters encode common characters into a fixed 6-bit field. They +represent the following characters with the following 6-bit values: + +:: + + 'a' .. 'z' --- 0 .. 25 + 'A' .. 'Z' --- 26 .. 51 + '0' .. '9' --- 52 .. 61 + '.' --- 62 + '_' --- 63 + +This encoding is only suitable for encoding characters and strings that consist +only of the above characters. It is completely incapable of encoding characters +not in the set. + +Word Alignment +^^^^^^^^^^^^^^ + +Occasionally, it is useful to emit zero bits until the bitstream is a multiple +of 32 bits. This ensures that the bit position in the stream can be represented +as a multiple of 32-bit words. + +Abbreviation IDs +---------------- + +A bitstream is a sequential series of `Blocks`_ and `Data Records`_. Both of +these start with an abbreviation ID encoded as a fixed-bitwidth field. The +width is specified by the current block, as described below. The value of the +abbreviation ID specifies either a builtin ID (which have special meanings, +defined below) or one of the abbreviation IDs defined for the current block by +the stream itself. + +The set of builtin abbrev IDs is: + +* 0 - `END_BLOCK`_ --- This abbrev ID marks the end of the current block. + +* 1 - `ENTER_SUBBLOCK`_ --- This abbrev ID marks the beginning of a new + block. + +* 2 - `DEFINE_ABBREV`_ --- This defines a new abbreviation. + +* 3 - `UNABBREV_RECORD`_ --- This ID specifies the definition of an + unabbreviated record. + +Abbreviation IDs 4 and above are defined by the stream itself, and specify an +`abbreviated record encoding`_. + +.. _Blocks: + +Blocks +------ + +Blocks in a bitstream denote nested regions of the stream, and are identified by +a content-specific id number (for example, LLVM IR uses an ID of 12 to represent +function bodies). Block IDs 0-7 are reserved for `standard blocks`_ whose +meaning is defined by Bitcode; block IDs 8 and greater are application +specific. Nested blocks capture the hierarchical structure of the data encoded +in it, and various properties are associated with blocks as the file is parsed. +Block definitions allow the reader to efficiently skip blocks in constant time +if the reader wants a summary of blocks, or if it wants to efficiently skip data +it does not understand. The LLVM IR reader uses this mechanism to skip function +bodies, lazily reading them on demand. + +When reading and encoding the stream, several properties are maintained for the +block. In particular, each block maintains: + +#. A current abbrev id width. This value starts at 2 at the beginning of the + stream, and is set every time a block record is entered. The block entry + specifies the abbrev id width for the body of the block. + +#. A set of abbreviations. Abbreviations may be defined within a block, in + which case they are only defined in that block (neither subblocks nor + enclosing blocks see the abbreviation). Abbreviations can also be defined + inside a `BLOCKINFO`_ block, in which case they are defined in all blocks + that match the ID that the ``BLOCKINFO`` block is describing. + +As sub blocks are entered, these properties are saved and the new sub-block has +its own set of abbreviations, and its own abbrev id width. When a sub-block is +popped, the saved values are restored. + +.. _ENTER_SUBBLOCK: + +ENTER_SUBBLOCK Encoding +^^^^^^^^^^^^^^^^^^^^^^^ + +:raw-html:`` +[ENTER_SUBBLOCK, blockid\ :sub:`vbr8`, newabbrevlen\ :sub:`vbr4`, , blocklen_32] +:raw-html:`` + +The ``ENTER_SUBBLOCK`` abbreviation ID specifies the start of a new block +record. The ``blockid`` value is encoded as an 8-bit VBR identifier, and +indicates the type of block being entered, which can be a `standard block`_ or +an application-specific block. The ``newabbrevlen`` value is a 4-bit VBR, which +specifies the abbrev id width for the sub-block. The ``blocklen`` value is a +32-bit aligned value that specifies the size of the subblock in 32-bit +words. This value allows the reader to skip over the entire block in one jump. + +.. _END_BLOCK: + +END_BLOCK Encoding +^^^^^^^^^^^^^^^^^^ + +``[END_BLOCK, ]`` + +The ``END_BLOCK`` abbreviation ID specifies the end of the current block record. +Its end is aligned to 32-bits to ensure that the size of the block is an even +multiple of 32-bits. + +.. _Data Records: + +Data Records +------------ + +Data records consist of a record code and a number of (up to) 64-bit integer +values. The interpretation of the code and values is application specific and +may vary between different block types. Records can be encoded either using an +unabbrev record, or with an abbreviation. In the LLVM IR format, for example, +there is a record which encodes the target triple of a module. The code is +``MODULE_CODE_TRIPLE``, and the values of the record are the ASCII codes for the +characters in the string. + +.. _UNABBREV_RECORD: + +UNABBREV_RECORD Encoding +^^^^^^^^^^^^^^^^^^^^^^^^ + +:raw-html:`` +[UNABBREV_RECORD, code\ :sub:`vbr6`, numops\ :sub:`vbr6`, op0\ :sub:`vbr6`, op1\ :sub:`vbr6`, ...] +:raw-html:`` + +An ``UNABBREV_RECORD`` provides a default fallback encoding, which is both +completely general and extremely inefficient. It can describe an arbitrary +record by emitting the code and operands as VBRs. + +For example, emitting an LLVM IR target triple as an unabbreviated record +requires emitting the ``UNABBREV_RECORD`` abbrevid, a vbr6 for the +``MODULE_CODE_TRIPLE`` code, a vbr6 for the length of the string, which is equal +to the number of operands, and a vbr6 for each character. Because there are no +letters with values less than 32, each letter would need to be emitted as at +least a two-part VBR, which means that each letter would require at least 12 +bits. This is not an efficient encoding, but it is fully general. + +.. _abbreviated record encoding: + +Abbreviated Record Encoding +^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +``[, fields...]`` + +An abbreviated record is a abbreviation id followed by a set of fields that are +encoded according to the `abbreviation definition`_. This allows records to be +encoded significantly more densely than records encoded with the +`UNABBREV_RECORD`_ type, and allows the abbreviation types to be specified in +the stream itself, which allows the files to be completely self describing. The +actual encoding of abbreviations is defined below. + +The record code, which is the first field of an abbreviated record, may be +encoded in the abbreviation definition (as a literal operand) or supplied in the +abbreviated record (as a Fixed or VBR operand value). + +.. _abbreviation definition: + +Abbreviations +------------- + +Abbreviations are an important form of compression for bitstreams. The idea is +to specify a dense encoding for a class of records once, then use that encoding +to emit many records. It takes space to emit the encoding into the file, but +the space is recouped (hopefully plus some) when the records that use it are +emitted. + +Abbreviations can be determined dynamically per client, per file. Because the +abbreviations are stored in the bitstream itself, different streams of the same +format can contain different sets of abbreviations according to the needs of the +specific stream. As a concrete example, LLVM IR files usually emit an +abbreviation for binary operators. If a specific LLVM module contained no or +few binary operators, the abbreviation does not need to be emitted. + +.. _DEFINE_ABBREV: + +DEFINE_ABBREV Encoding +^^^^^^^^^^^^^^^^^^^^^^ + +:raw-html:`` +[DEFINE_ABBREV, numabbrevops\ :sub:`vbr5`, abbrevop0, abbrevop1, ...] +:raw-html:`` + +A ``DEFINE_ABBREV`` record adds an abbreviation to the list of currently defined +abbreviations in the scope of this block. This definition only exists inside +this immediate block --- it is not visible in subblocks or enclosing blocks. +Abbreviations are implicitly assigned IDs sequentially starting from 4 (the +first application-defined abbreviation ID). Any abbreviations defined in a +``BLOCKINFO`` record for the particular block type receive IDs first, in order, +followed by any abbreviations defined within the block itself. Abbreviated data +records reference this ID to indicate what abbreviation they are invoking. + +An abbreviation definition consists of the ``DEFINE_ABBREV`` abbrevid followed +by a VBR that specifies the number of abbrev operands, then the abbrev operands +themselves. Abbreviation operands come in three forms. They all start with a +single bit that indicates whether the abbrev operand is a literal operand (when +the bit is 1) or an encoding operand (when the bit is 0). + +#. Literal operands --- :raw-html:`` [1\ :sub:`1`, litvalue\ + :sub:`vbr8`] :raw-html:`` --- Literal operands specify that the value in + the result is always a single specific value. This specific value is emitted + as a vbr8 after the bit indicating that it is a literal operand. + +#. Encoding info without data --- :raw-html:`` [0\ :sub:`1`, encoding\ + :sub:`3`] :raw-html:`` --- Operand encodings that do not have extra data + are just emitted as their code. + +#. Encoding info with data --- :raw-html:`` [0\ :sub:`1`, encoding\ + :sub:`3`, value\ :sub:`vbr5`] :raw-html:`` --- Operand encodings that do + have extra data are emitted as their code, followed by the extra data. + +The possible operand encodings are: + +* Fixed (code 1): The field should be emitted as a `fixed-width value`_, whose + width is specified by the operand's extra data. + +* VBR (code 2): The field should be emitted as a `variable-width value`_, whose + width is specified by the operand's extra data. + +* Array (code 3): This field is an array of values. The array operand has no + extra data, but expects another operand to follow it, indicating the element + type of the array. When reading an array in an abbreviated record, the first + integer is a vbr6 that indicates the array length, followed by the encoded + elements of the array. An array may only occur as the last operand of an + abbreviation (except for the one final operand that gives the array's + type). + +* Char6 (code 4): This field should be emitted as a `char6-encoded value`_. + This operand type takes no extra data. Char6 encoding is normally used as an + array element type. + +* Blob (code 5): This field is emitted as a vbr6, followed by padding to a + 32-bit boundary (for alignment) and an array of 8-bit objects. The array of + bytes is further followed by tail padding to ensure that its total length is a + multiple of 4 bytes. This makes it very efficient for the reader to decode + the data without having to make a copy of it: it can use a pointer to the data + in the mapped in file and poke directly at it. A blob may only occur as the + last operand of an abbreviation. + +For example, target triples in LLVM modules are encoded as a record of the form +``[TRIPLE, 'a', 'b', 'c', 'd']``. Consider if the bitstream emitted the +following abbrev entry: + +:: + + [0, Fixed, 4] + [0, Array] + [0, Char6] + +When emitting a record with this abbreviation, the above entry would be emitted +as: + +:raw-html:`
` +[4\ :sub:`abbrevwidth`, 2\ :sub:`4`, 4\ :sub:`vbr6`, 0\ :sub:`6`, 1\ :sub:`6`, 2\ :sub:`6`, 3\ :sub:`6`] +:raw-html:`
` + +These values are: + +#. The first value, 4, is the abbreviation ID for this abbreviation. + +#. The second value, 2, is the record code for ``TRIPLE`` records within LLVM IR + file ``MODULE_BLOCK`` blocks. + +#. The third value, 4, is the length of the array. + +#. The rest of the values are the char6 encoded values for ``"abcd"``. + +With this abbreviation, the triple is emitted with only 37 bits (assuming a +abbrev id width of 3). Without the abbreviation, significantly more space would +be required to emit the target triple. Also, because the ``TRIPLE`` value is +not emitted as a literal in the abbreviation, the abbreviation can also be used +for any other string value. + +.. _standard blocks: +.. _standard block: + +Standard Blocks +--------------- + +In addition to the basic block structure and record encodings, the bitstream +also defines specific built-in block types. These block types specify how the +stream is to be decoded or other metadata. In the future, new standard blocks +may be added. Block IDs 0-7 are reserved for standard blocks. + +.. _BLOCKINFO: + +#0 - BLOCKINFO Block +^^^^^^^^^^^^^^^^^^^^ + +The ``BLOCKINFO`` block allows the description of metadata for other blocks. +The currently specified records are: + +:: + + [SETBID (#1), blockid] + [DEFINE_ABBREV, ...] + [BLOCKNAME, ...name...] + [SETRECORDNAME, RecordID, ...name...] + +The ``SETBID`` record (code 1) indicates which block ID is being described. +``SETBID`` records can occur multiple times throughout the block to change which +block ID is being described. There must be a ``SETBID`` record prior to any +other records. + +Standard ``DEFINE_ABBREV`` records can occur inside ``BLOCKINFO`` blocks, but +unlike their occurrence in normal blocks, the abbreviation is defined for blocks +matching the block ID we are describing, *not* the ``BLOCKINFO`` block +itself. The abbreviations defined in ``BLOCKINFO`` blocks receive abbreviation +IDs as described in `DEFINE_ABBREV`_. + +The ``BLOCKNAME`` record (code 2) can optionally occur in this block. The +elements of the record are the bytes of the string name of the block. +llvm-bcanalyzer can use this to dump out bitcode files symbolically. + +The ``SETRECORDNAME`` record (code 3) can also optionally occur in this block. +The first operand value is a record ID number, and the rest of the elements of +the record are the bytes for the string name of the record. llvm-bcanalyzer can +use this to dump out bitcode files symbolically. + +Note that although the data in ``BLOCKINFO`` blocks is described as "metadata," +the abbreviations they contain are essential for parsing records from the +corresponding blocks. It is not safe to skip them. + +.. _wrapper: + +Bitcode Wrapper Format +====================== + +Bitcode files for LLVM IR may optionally be wrapped in a simple wrapper +structure. This structure contains a simple header that indicates the offset +and size of the embedded BC file. This allows additional information to be +stored alongside the BC file. The structure of this file header is: + +:raw-html:`
` +[Magic\ :sub:`32`, Version\ :sub:`32`, Offset\ :sub:`32`, Size\ :sub:`32`, CPUType\ :sub:`32`] +:raw-html:`
` + +Each of the fields are 32-bit fields stored in little endian form (as with the +rest of the bitcode file fields). The Magic number is always ``0x0B17C0DE`` and +the version is currently always ``0``. The Offset field is the offset in bytes +to the start of the bitcode stream in the file, and the Size field is the size +in bytes of the stream. CPUType is a target-specific value that can be used to +encode the CPU of the target. + +.. _encoding of LLVM IR: + +LLVM IR Encoding +================ + +LLVM IR is encoded into a bitstream by defining blocks and records. It uses +blocks for things like constant pools, functions, symbol tables, etc. It uses +records for things like instructions, global variable descriptors, type +descriptions, etc. This document does not describe the set of abbreviations +that the writer uses, as these are fully self-described in the file, and the +reader is not allowed to build in any knowledge of this. + +Basics +------ + +LLVM IR Magic Number +^^^^^^^^^^^^^^^^^^^^ + +The magic number for LLVM IR files is: + +:raw-html:`
` +[0x0\ :sub:`4`, 0xC\ :sub:`4`, 0xE\ :sub:`4`, 0xD\ :sub:`4`] +:raw-html:`
` + +When combined with the bitcode magic number and viewed as bytes, this is +``"BC 0xC0DE"``. + +Signed VBRs +^^^^^^^^^^^ + +`Variable Width Integer`_ encoding is an efficient way to encode arbitrary sized +unsigned values, but is an extremely inefficient for encoding signed values, as +signed values are otherwise treated as maximally large unsigned values. + +As such, signed VBR values of a specific width are emitted as follows: + +* Positive values are emitted as VBRs of the specified width, but with their + value shifted left by one. + +* Negative values are emitted as VBRs of the specified width, but the negated + value is shifted left by one, and the low bit is set. + +With this encoding, small positive and small negative values can both be emitted +efficiently. Signed VBR encoding is used in ``CST_CODE_INTEGER`` and +``CST_CODE_WIDE_INTEGER`` records within ``CONSTANTS_BLOCK`` blocks. + +LLVM IR Blocks +^^^^^^^^^^^^^^ + +LLVM IR is defined with the following blocks: + +* 8 --- `MODULE_BLOCK`_ --- This is the top-level block that contains the entire + module, and describes a variety of per-module information. + +* 9 --- `PARAMATTR_BLOCK`_ --- This enumerates the parameter attributes. + +* 10 --- `TYPE_BLOCK`_ --- This describes all of the types in the module. + +* 11 --- `CONSTANTS_BLOCK`_ --- This describes constants for a module or + function. + +* 12 --- `FUNCTION_BLOCK`_ --- This describes a function body. + +* 13 --- `TYPE_SYMTAB_BLOCK`_ --- This describes the type symbol table. + +* 14 --- `VALUE_SYMTAB_BLOCK`_ --- This describes a value symbol table. + +* 15 --- `METADATA_BLOCK`_ --- This describes metadata items. + +* 16 --- `METADATA_ATTACHMENT`_ --- This contains records associating metadata + with function instruction values. + +.. _MODULE_BLOCK: + +MODULE_BLOCK Contents +--------------------- + +The ``MODULE_BLOCK`` block (id 8) is the top-level block for LLVM bitcode files, +and each bitcode file must contain exactly one. In addition to records +(described below) containing information about the module, a ``MODULE_BLOCK`` +block may contain the following sub-blocks: + +* `BLOCKINFO`_ +* `PARAMATTR_BLOCK`_ +* `TYPE_BLOCK`_ +* `TYPE_SYMTAB_BLOCK`_ +* `VALUE_SYMTAB_BLOCK`_ +* `CONSTANTS_BLOCK`_ +* `FUNCTION_BLOCK`_ +* `METADATA_BLOCK`_ + +MODULE_CODE_VERSION Record +^^^^^^^^^^^^^^^^^^^^^^^^^^ + +``[VERSION, version#]`` + +The ``VERSION`` record (code 1) contains a single value indicating the format +version. Only version 0 is supported at this time. + +MODULE_CODE_TRIPLE Record +^^^^^^^^^^^^^^^^^^^^^^^^^ + +``[TRIPLE, ...string...]`` + +The ``TRIPLE`` record (code 2) contains a variable number of values representing +the bytes of the ``target triple`` specification string. + +MODULE_CODE_DATALAYOUT Record +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +``[DATALAYOUT, ...string...]`` + +The ``DATALAYOUT`` record (code 3) contains a variable number of values +representing the bytes of the ``target datalayout`` specification string. + +MODULE_CODE_ASM Record +^^^^^^^^^^^^^^^^^^^^^^ + +``[ASM, ...string...]`` + +The ``ASM`` record (code 4) contains a variable number of values representing +the bytes of ``module asm`` strings, with individual assembly blocks separated +by newline (ASCII 10) characters. + +.. _MODULE_CODE_SECTIONNAME: + +MODULE_CODE_SECTIONNAME Record +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +``[SECTIONNAME, ...string...]`` + +The ``SECTIONNAME`` record (code 5) contains a variable number of values +representing the bytes of a single section name string. There should be one +``SECTIONNAME`` record for each section name referenced (e.g., in global +variable or function ``section`` attributes) within the module. These records +can be referenced by the 1-based index in the *section* fields of ``GLOBALVAR`` +or ``FUNCTION`` records. + +MODULE_CODE_DEPLIB Record +^^^^^^^^^^^^^^^^^^^^^^^^^ + +``[DEPLIB, ...string...]`` + +The ``DEPLIB`` record (code 6) contains a variable number of values representing +the bytes of a single dependent library name string, one of the libraries +mentioned in a ``deplibs`` declaration. There should be one ``DEPLIB`` record +for each library name referenced. + +MODULE_CODE_GLOBALVAR Record +^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +``[GLOBALVAR, pointer type, isconst, initid, linkage, alignment, section, visibility, threadlocal, unnamed_addr]`` + +The ``GLOBALVAR`` record (code 7) marks the declaration or definition of a +global variable. The operand fields are: + +* *pointer type*: The type index of the pointer type used to point to this + global variable + +* *isconst*: Non-zero if the variable is treated as constant within the module, + or zero if it is not + +* *initid*: If non-zero, the value index of the initializer for this variable, + plus 1. + +.. _linkage type: + +* *linkage*: An encoding of the linkage type for this variable: + * ``external``: code 0 + * ``weak``: code 1 + * ``appending``: code 2 + * ``internal``: code 3 + * ``linkonce``: code 4 + * ``dllimport``: code 5 + * ``dllexport``: code 6 + * ``extern_weak``: code 7 + * ``common``: code 8 + * ``private``: code 9 + * ``weak_odr``: code 10 + * ``linkonce_odr``: code 11 + * ``available_externally``: code 12 + * ``linker_private``: code 13 + +* alignment*: The logarithm base 2 of the variable's requested alignment, plus 1 + +* *section*: If non-zero, the 1-based section index in the table of + `MODULE_CODE_SECTIONNAME`_ entries. + +.. _visibility: + +* *visibility*: If present, an encoding of the visibility of this variable: + * ``default``: code 0 + * ``hidden``: code 1 + * ``protected``: code 2 + +* *threadlocal*: If present, an encoding of the thread local storage mode of the + variable: + * ``not thread local``: code 0 + * ``thread local; default TLS model``: code 1 + * ``localdynamic``: code 2 + * ``initialexec``: code 3 + * ``localexec``: code 4 + +* *unnamed_addr*: If present and non-zero, indicates that the variable has + ``unnamed_addr`` + +.. _FUNCTION: + +MODULE_CODE_FUNCTION Record +^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +``[FUNCTION, type, callingconv, isproto, linkage, paramattr, alignment, section, visibility, gc]`` + +The ``FUNCTION`` record (code 8) marks the declaration or definition of a +function. The operand fields are: + +* *type*: The type index of the function type describing this function + +* *callingconv*: The calling convention number: + * ``ccc``: code 0 + * ``fastcc``: code 8 + * ``coldcc``: code 9 + * ``x86_stdcallcc``: code 64 + * ``x86_fastcallcc``: code 65 + * ``arm_apcscc``: code 66 + * ``arm_aapcscc``: code 67 + * ``arm_aapcs_vfpcc``: code 68 + +* isproto*: Non-zero if this entry represents a declaration rather than a + definition + +* *linkage*: An encoding of the `linkage type`_ for this function + +* *paramattr*: If nonzero, the 1-based parameter attribute index into the table + of `PARAMATTR_CODE_ENTRY`_ entries. + +* *alignment*: The logarithm base 2 of the function's requested alignment, plus + 1 + +* *section*: If non-zero, the 1-based section index in the table of + `MODULE_CODE_SECTIONNAME`_ entries. + +* *visibility*: An encoding of the `visibility`_ of this function + +* *gc*: If present and nonzero, the 1-based garbage collector index in the table + of `MODULE_CODE_GCNAME`_ entries. + +* *unnamed_addr*: If present and non-zero, indicates that the function has + ``unnamed_addr`` + +MODULE_CODE_ALIAS Record +^^^^^^^^^^^^^^^^^^^^^^^^ + +``[ALIAS, alias type, aliasee val#, linkage, visibility]`` + +The ``ALIAS`` record (code 9) marks the definition of an alias. The operand +fields are + +* *alias type*: The type index of the alias + +* *aliasee val#*: The value index of the aliased value + +* *linkage*: An encoding of the `linkage type`_ for this alias + +* *visibility*: If present, an encoding of the `visibility`_ of the alias + +MODULE_CODE_PURGEVALS Record +^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +``[PURGEVALS, numvals]`` + +The ``PURGEVALS`` record (code 10) resets the module-level value list to the +size given by the single operand value. Module-level value list items are added +by ``GLOBALVAR``, ``FUNCTION``, and ``ALIAS`` records. After a ``PURGEVALS`` +record is seen, new value indices will start from the given *numvals* value. + +.. _MODULE_CODE_GCNAME: + +MODULE_CODE_GCNAME Record +^^^^^^^^^^^^^^^^^^^^^^^^^ + +``[GCNAME, ...string...]`` + +The ``GCNAME`` record (code 11) contains a variable number of values +representing the bytes of a single garbage collector name string. There should +be one ``GCNAME`` record for each garbage collector name referenced in function +``gc`` attributes within the module. These records can be referenced by 1-based +index in the *gc* fields of ``FUNCTION`` records. + +.. _PARAMATTR_BLOCK: + +PARAMATTR_BLOCK Contents +------------------------ + +The ``PARAMATTR_BLOCK`` block (id 9) contains a table of entries describing the +attributes of function parameters. These entries are referenced by 1-based index +in the *paramattr* field of module block `FUNCTION`_ records, or within the +*attr* field of function block ``INST_INVOKE`` and ``INST_CALL`` records. + +Entries within ``PARAMATTR_BLOCK`` are constructed to ensure that each is unique +(i.e., no two indicies represent equivalent attribute lists). + +.. _PARAMATTR_CODE_ENTRY: + +PARAMATTR_CODE_ENTRY Record +^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +``[ENTRY, paramidx0, attr0, paramidx1, attr1...]`` + +The ``ENTRY`` record (code 1) contains an even number of values describing a +unique set of function parameter attributes. Each *paramidx* value indicates +which set of attributes is represented, with 0 representing the return value +attributes, 0xFFFFFFFF representing function attributes, and other values +representing 1-based function parameters. Each *attr* value is a bitmap with the +following interpretation: + +* bit 0: ``zeroext`` +* bit 1: ``signext`` +* bit 2: ``noreturn`` +* bit 3: ``inreg`` +* bit 4: ``sret`` +* bit 5: ``nounwind`` +* bit 6: ``noalias`` +* bit 7: ``byval`` +* bit 8: ``nest`` +* bit 9: ``readnone`` +* bit 10: ``readonly`` +* bit 11: ``noinline`` +* bit 12: ``alwaysinline`` +* bit 13: ``optsize`` +* bit 14: ``ssp`` +* bit 15: ``sspreq`` +* bits 16-31: ``align n`` +* bit 32: ``nocapture`` +* bit 33: ``noredzone`` +* bit 34: ``noimplicitfloat`` +* bit 35: ``naked`` +* bit 36: ``inlinehint`` +* bits 37-39: ``alignstack n``, represented as the logarithm + base 2 of the requested alignment, plus 1 + +.. _TYPE_BLOCK: + +TYPE_BLOCK Contents +------------------- + +The ``TYPE_BLOCK`` block (id 10) contains records which constitute a table of +type operator entries used to represent types referenced within an LLVM +module. Each record (with the exception of `NUMENTRY`_) generates a single type +table entry, which may be referenced by 0-based index from instructions, +constants, metadata, type symbol table entries, or other type operator records. + +Entries within ``TYPE_BLOCK`` are constructed to ensure that each entry is +unique (i.e., no two indicies represent structurally equivalent types). + +.. _TYPE_CODE_NUMENTRY: +.. _NUMENTRY: + +TYPE_CODE_NUMENTRY Record +^^^^^^^^^^^^^^^^^^^^^^^^^ + +``[NUMENTRY, numentries]`` + +The ``NUMENTRY`` record (code 1) contains a single value which indicates the +total number of type code entries in the type table of the module. If present, +``NUMENTRY`` should be the first record in the block. + +TYPE_CODE_VOID Record +^^^^^^^^^^^^^^^^^^^^^ + +``[VOID]`` + +The ``VOID`` record (code 2) adds a ``void`` type to the type table. + +TYPE_CODE_HALF Record +^^^^^^^^^^^^^^^^^^^^^ + +``[HALF]`` + +The ``HALF`` record (code 10) adds a ``half`` (16-bit floating point) type to +the type table. + +TYPE_CODE_FLOAT Record +^^^^^^^^^^^^^^^^^^^^^^ + +``[FLOAT]`` + +The ``FLOAT`` record (code 3) adds a ``float`` (32-bit floating point) type to +the type table. + +TYPE_CODE_DOUBLE Record +^^^^^^^^^^^^^^^^^^^^^^^ + +``[DOUBLE]`` + +The ``DOUBLE`` record (code 4) adds a ``double`` (64-bit floating point) type to +the type table. + +TYPE_CODE_LABEL Record +^^^^^^^^^^^^^^^^^^^^^^ + +``[LABEL]`` + +The ``LABEL`` record (code 5) adds a ``label`` type to the type table. + +TYPE_CODE_OPAQUE Record +^^^^^^^^^^^^^^^^^^^^^^^ + +``[OPAQUE]`` + +The ``OPAQUE`` record (code 6) adds an ``opaque`` type to the type table. Note +that distinct ``opaque`` types are not unified. + +TYPE_CODE_INTEGER Record +^^^^^^^^^^^^^^^^^^^^^^^^ + +``[INTEGER, width]`` + +The ``INTEGER`` record (code 7) adds an integer type to the type table. The +single *width* field indicates the width of the integer type. + +TYPE_CODE_POINTER Record +^^^^^^^^^^^^^^^^^^^^^^^^ + +``[POINTER, pointee type, address space]`` + +The ``POINTER`` record (code 8) adds a pointer type to the type table. The +operand fields are + +* *pointee type*: The type index of the pointed-to type + +* *address space*: If supplied, the target-specific numbered address space where + the pointed-to object resides. Otherwise, the default address space is zero. + +TYPE_CODE_FUNCTION Record +^^^^^^^^^^^^^^^^^^^^^^^^^ + +``[FUNCTION, vararg, ignored, retty, ...paramty... ]`` + +The ``FUNCTION`` record (code 9) adds a function type to the type table. The +operand fields are + +* *vararg*: Non-zero if the type represents a varargs function + +* *ignored*: This value field is present for backward compatibility only, and is + ignored + +* *retty*: The type index of the function's return type + +* *paramty*: Zero or more type indices representing the parameter types of the + function + +TYPE_CODE_STRUCT Record +^^^^^^^^^^^^^^^^^^^^^^^ + +``[STRUCT, ispacked, ...eltty...]`` + +The ``STRUCT`` record (code 10) adds a struct type to the type table. The +operand fields are + +* *ispacked*: Non-zero if the type represents a packed structure + +* *eltty*: Zero or more type indices representing the element types of the + structure + +TYPE_CODE_ARRAY Record +^^^^^^^^^^^^^^^^^^^^^^ + +``[ARRAY, numelts, eltty]`` + +The ``ARRAY`` record (code 11) adds an array type to the type table. The +operand fields are + +* *numelts*: The number of elements in arrays of this type + +* *eltty*: The type index of the array element type + +TYPE_CODE_VECTOR Record +^^^^^^^^^^^^^^^^^^^^^^^ + +``[VECTOR, numelts, eltty]`` + +The ``VECTOR`` record (code 12) adds a vector type to the type table. The +operand fields are + +* *numelts*: The number of elements in vectors of this type + +* *eltty*: The type index of the vector element type + +TYPE_CODE_X86_FP80 Record +^^^^^^^^^^^^^^^^^^^^^^^^^ + +``[X86_FP80]`` + +The ``X86_FP80`` record (code 13) adds an ``x86_fp80`` (80-bit floating point) +type to the type table. + +TYPE_CODE_FP128 Record +^^^^^^^^^^^^^^^^^^^^^^ + +``[FP128]`` + +The ``FP128`` record (code 14) adds an ``fp128`` (128-bit floating point) type +to the type table. + +TYPE_CODE_PPC_FP128 Record +^^^^^^^^^^^^^^^^^^^^^^^^^^ + +``[PPC_FP128]`` + +The ``PPC_FP128`` record (code 15) adds a ``ppc_fp128`` (128-bit floating point) +type to the type table. + +TYPE_CODE_METADATA Record +^^^^^^^^^^^^^^^^^^^^^^^^^ + +``[METADATA]`` + +The ``METADATA`` record (code 16) adds a ``metadata`` type to the type table. + +.. _CONSTANTS_BLOCK: + +CONSTANTS_BLOCK Contents +------------------------ + +The ``CONSTANTS_BLOCK`` block (id 11) ... + +.. _FUNCTION_BLOCK: + +FUNCTION_BLOCK Contents +----------------------- + +The ``FUNCTION_BLOCK`` block (id 12) ... + +In addition to the record types described below, a ``FUNCTION_BLOCK`` block may +contain the following sub-blocks: + +* `CONSTANTS_BLOCK`_ +* `VALUE_SYMTAB_BLOCK`_ +* `METADATA_ATTACHMENT`_ + +.. _TYPE_SYMTAB_BLOCK: + +TYPE_SYMTAB_BLOCK Contents +-------------------------- + +The ``TYPE_SYMTAB_BLOCK`` block (id 13) contains entries which map between +module-level named types and their corresponding type indices. + +.. _TST_CODE_ENTRY: + +TST_CODE_ENTRY Record +^^^^^^^^^^^^^^^^^^^^^ + +``[ENTRY, typeid, ...string...]`` + +The ``ENTRY`` record (code 1) contains a variable number of values, with the +first giving the type index of the designated type, and the remaining values +giving the character codes of the type name. Each entry corresponds to a single +named type. + +.. _VALUE_SYMTAB_BLOCK: + +VALUE_SYMTAB_BLOCK Contents +--------------------------- + +The ``VALUE_SYMTAB_BLOCK`` block (id 14) ... + +.. _METADATA_BLOCK: + +METADATA_BLOCK Contents +----------------------- + +The ``METADATA_BLOCK`` block (id 15) ... + +.. _METADATA_ATTACHMENT: + +METADATA_ATTACHMENT Contents +---------------------------- + +The ``METADATA_ATTACHMENT`` block (id 16) ... -- cgit v1.1