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[ctf.git] / common-trace-format-specification.md

# Common Trace Format (CTF) Specification (v1.8.2)

**Author**: Mathieu Desnoyers, [EfficiOS Inc.](http://www.efficios.com/)

The goal of the present document is to specify a trace format that suits
the needs of the embedded, telecom, high-performance and kernel
communities. It is based on the
[Common Trace Format Requirements (v1.4)](http://git.efficios.com/?p=ctf.git;a=blob_plain;f=common-trace-format-reqs.txt;hb=master)
document. It is designed to allow traces to be natively generated by the
Linux kernel, Linux user space applications written in C/C++, and
hardware components. One major element of CTF is the Trace Stream
Description Language (TSDL) which flexibility enables description of
various binary trace stream layouts.

The latest version of this document can be found at:

  * Git: `git clone git://git.efficios.com/ctf.git`
  * [Gitweb](http://git.efficios.com/?p=ctf.git)

A reference implementation of a library to read and write this trace
format is being implemented within the
[Babeltrace](http://www.efficios.com/babeltrace) project, a converter
between trace formats. The development tree is available at:

  * Git: `git clone git://git.efficios.com/babeltrace.git`
  * [Gitweb](http://git.efficios.com/?p=babeltrace.git)

The [CE Workgroup](http://www.linuxfoundation.org/collaborate/workgroups/celf)
of the Linux Foundation, [Ericsson](http://www.ericsson.com/), and
[EfficiOS](http://www.efficios.com/) have sponsored this work.

**Contents**:

    1. Preliminary definitions
    2. High-level representation of a trace
    3. Event stream
    4. Types
      4.1 Basic types
        4.1.1 Type inheritance
        4.1.2 Alignment
        4.1.3 Byte order
        4.1.4 Size
        4.1.5 Integers
        4.1.6 GNU/C bitfields
        4.1.7 Floating point
        4.1.8 Enumerations
      4.2 Compound types
        4.2.1 Structures
        4.2.2 Variants (discriminated/tagged unions)
        4.2.3 Arrays
        4.2.4 Sequences
        4.2.5 Strings
    5. Event packet header
      5.1 Event packet header description
      5.2 Event packet context description
    6. Event structure
      6.1 Event header
        6.1.1 Type 1: few event IDs
        6.1.2 Type 2: many event IDs
      6.2 Stream event context and event context
      6.3 Event payload
        6.3.1 Padding
        6.3.2 Alignment
    7. Trace Stream Description Language (TSDL)
      7.1 Metadata
      7.2 Declaration vs definition
      7.3 TSDL scopes
        7.3.1 Lexical scope
        7.3.2 Static and dynamic scopes
      7.4 TSDL examples
    8. Clocks
    A. Helper macros
    B. Stream header rationale
    C. TSDL Grammar
      C.1 Lexical grammar
        C.1.1 Lexical elements
        C.1.2 Keywords
        C.1.3 Identifiers
        C.1.4 Universal character names
        C.1.5 Constants
        C.1.6 String literals
        C.1.7 Punctuators
      C.2 Phrase structure grammar
        C.2.2 Declarations:
        C.2.3 CTF-specific declarations


## 1. Preliminary definitions

  * **Event trace**: an ordered sequence of events.
  * **Event stream**: an ordered sequence of events, containing a
    subset of the trace event types.
  * **Event packet**: a sequence of physically contiguous events within
    an event stream.
  * **Event**: this is the basic entry in a trace. Also known as
    a _trace record_.
    * An **event identifier** (ID) relates to the class (a type) of
      event within an event stream, e.g. event `irq_entry`.
    * An **event** (or event record) relates to a specific instance of
      an event class, e.g. event `irq_entry`, at time _X_, on CPU _Y_.
  * Source architecture: architecture writing the trace.
  * Reader architecture: architecture reading the trace.


## 2. High-level representation of a trace

A _trace_ is divided into multiple event streams. Each event stream
contains a subset of the trace event types.

The final output of the trace, after its generation and optional
transport over the network, is expected to be either on permanent or
temporary storage in a virtual file system. Because each event stream
is appended to while a trace is being recorded, each is associated with
a distinct set of files for output. Therefore, a stored trace can be
represented as a directory containing zero, one or more files
per stream.

Metadata description associated with the trace contains information on
trace event types expressed in the _Trace Stream Description Language_
(TSDL). This language describes:

  * Trace version
  * Types available
  * Per-trace event header description
  * Per-stream event header description
  * Per-stream event context description
  * Per-event
    * Event type to stream mapping
    * Event type to name mapping
    * Event type to ID mapping
    * Event context description
    * Event fields description


## 3. Event stream

An _event stream_ can be divided into contiguous event packets of
variable size. An event packet can contain a certain amount of padding
at the end. The stream header is repeated at the beginning of each
event packet. The rationale for the event stream design choices is
explained in [Stream header rationale](#specB).

The event stream header will therefore be referred to as the
_event packet header_ throughout the rest of this document.


## 4. Types

Types are organized as type classes. Each type class belong to either
of two kind of types: _basic types_ or _compound types_.


### 4.1 Basic types

A basic type is a scalar type, as described in this section. It
includes integers, GNU/C bitfields, enumerations, and floating
point values.


#### 4.1.1 Type inheritance

Type specifications can be inherited to allow deriving types from a
type class. For example, see the uint32_t named type derived from the
[_integer_ type](#spec4.1.5) class. Types have a precise binary
representation in the trace. A type class has methods to read and write
these types, but must be derived into a type to be usable in an event
field.


#### 4.1.2 Alignment

We define _byte-packed_ types as aligned on the byte size, namely 8-bit.
We define _bit-packed_ types as following on the next bit, as defined
by the [Integers](#spec4.1.5) section.

Each basic type must specify its alignment, in bits. Examples of
possible alignments are: bit-packed (`align = 1`), byte-packed
(`align = 8`), or word-aligned (e.g. `align = 32` or `align = 64`).
The choice depends on the architecture preference and compactness vs
performance trade-offs of the implementation. Architectures providing
fast unaligned write byte-packed basic types to save space, aligning
each type on byte boundaries (8-bit). Architectures with slow unaligned
writes align types on specific alignment values. If no specific
alignment is declared for a type, it is assumed to be bit-packed for
integers with size not multiple of 8 bits and for gcc bitfields. All
other basic types are byte-packed by default. It is however recommended
to always specify the alignment explicitly. Alignment values must be
power of two. Compound types are aligned as specified in their
individual specification.

The base offset used for field alignment is the start of the packet
containing the field. For instance, a field aligned on 32-bit needs to
be at an offset multiple of 32-bit from the start of the packet that
contains it.

TSDL metadata attribute representation of a specific alignment:

~~~ tsdl
align = /* value in bits */;
~~~

#### 4.1.3 Byte order

By default, byte order of a basic type is the byte order described in
the trace description. It can be overridden by specifying a
`byte_order` attribute for a basic type.  Typical use-case is to specify
the network byte order (big endian: `be`) to save data captured from
the network into the trace without conversion.

TSDL metadata representation:

~~~ tsdl
/* network and be are aliases */
byte_order = /* native OR network OR be OR le */;
~~~

The `native` keyword selects the byte order described in the trace
description. The `network` byte order is an alias for big endian.

Even though the trace description section is not per se a type, for
sake of clarity, it should be noted that `native` and `network` byte
orders are only allowed within type declaration. The `byte_order`
specified in the trace description section only accepts `be` or `le`
values.


#### 4.1.4 Size

Type size, in bits, for integers and floats is that returned by
`sizeof()` in C multiplied by `CHAR_BIT`. We require the size of `char`
and `unsigned char` types (`CHAR_BIT`) to be fixed to 8 bits for
cross-endianness compatibility.

TSDL metadata representation:

~~~ tsdl
size = /* value is in bits */;
~~~


#### 4.1.5 Integers

Signed integers are represented in two-complement. Integer alignment,
size, signedness and byte ordering are defined in the TSDL metadata.
Integers aligned on byte size (8-bit) and with length multiple of byte
size (8-bit) correspond to the C99 standard integers. In addition,
integers with alignment and/or size that are _not_ a multiple of the
byte size are permitted; these correspond to the C99 standard bitfields,
with the added specification that the CTF integer bitfields have a fixed
binary representation. Integer size needs to be a positive integer.
Integers of size 0 are **forbidden**. An MIT-licensed reference
implementation of the CTF portable bitfields is available
[here](http://git.efficios.com/?p=babeltrace.git;a=blob;f=include/babeltrace/bitfield.h).

Binary representation of integers:

  * On little and big endian:
    * Within a byte, high bits correspond to an integer high bits, and
      low bits correspond to low bits
  * On little endian:
    * Integer across multiple bytes are placed from the less significant
      to the most significant
    * Consecutive integers are placed from lower bits to higher bits
      (even within a byte)
  * On big endian:
    * Integer across multiple bytes are placed from the most significant
      to the less significant
    * Consecutive integers are placed from higher bits to lower bits
      (even within a byte)

This binary representation is derived from the bitfield implementation
in GCC for little and big endian. However, contrary to what GCC does,
integers can cross units boundaries (no padding is required). Padding
can be [explicitly added](#spec4.1.6) to follow the GCC layout if needed.

TSDL metadata representation:

~~~ tsdl
integer {
    signed = /* true OR false */;                     /* default: false */
    byte_order = /* native OR network OR be OR le */; /* default: native */
    size = /* value in bits */;                       /* no default */
    align = /* value in bits */;

    /* base used for pretty-printing output; default: decimal */
    base = /* decimal OR dec OR d OR i OR u OR 10 OR hexadecimal OR hex
              OR x OR X OR p OR 16 OR octal OR oct OR o OR 8 OR binary
              OR b OR 2 */;

    /* character encoding */
    encoding = /* none or UTF8 or ASCII */;           /* default: none */
}
~~~

Example of type inheritance (creation of a `uint32_t` named type):

~~~ tsdl
typealias integer {
    size = 32;
    signed = false;
    align = 32;
} := uint32_t;
~~~

Definition of a named 5-bit signed bitfield:

~~~ tsdl
typealias integer {
    size = 5;
    signed = true;
    align = 1;
} := int5_t;
~~~

The character encoding field can be used to specify that the integer
must be printed as a text character when read. e.g.:

~~~ tsdl
typealias integer {
    size = 8;
    align = 8;
    signed = false;
    encoding = UTF8;
} := utf_char;
~~~

#### 4.1.6 GNU/C bitfields

The GNU/C bitfields follow closely the integer representation, with a
particularity on alignment: if a bitfield cannot fit in the current
unit, the unit is padded and the bitfield starts at the following unit.
The unit size is defined by the size of the type `unit_type`.

TSDL metadata representation:

~~~ tsdl
unit_type name:size;
~~~

As an example, the following structure declared in C compiled by GCC:

~~~ tsdl
struct example {
    short a:12;
    short b:5;
};
~~~

The example structure is aligned on the largest element (short). The
second bitfield would be aligned on the next unit boundary, because it
would not fit in the current unit.


#### 4.1.7 Floating point

The floating point values byte ordering is defined in the TSDL metadata.

Floating point values follow the IEEE 754-2008 standard interchange
formats. Description of the floating point values include the exponent
and mantissa size in bits. Some requirements are imposed on the
floating point values:

* `FLT_RADIX` must be 2.
* `mant_dig` is the number of digits represented in the mantissa. It is
  specified by the ISO C99 standard, section 5.2.4, as `FLT_MANT_DIG`,
  `DBL_MANT_DIG` and `LDBL_MANT_DIG` as defined by `<float.h>`.
* `exp_dig` is the number of digits represented in the exponent. Given
  that `mant_dig` is one bit more than its actual size in bits (leading
  1 is not needed) and also given that the sign bit always takes one
  bit, `exp_dig` can be specified as:
  * `sizeof(float) * CHAR_BIT - FLT_MANT_DIG`
  * `sizeof(double) * CHAR_BIT - DBL_MANT_DIG`
  * `sizeof(long double) * CHAR_BIT - LDBL_MANT_DIG`

TSDL metadata representation:

~~~ tsdl
floating_point {
    exp_dig = /* value */;
    mant_dig = /* value */;
    byte_order = /* native OR network OR be OR le */;
    align = /* value */;
}
~~~

Example of type inheritance:

~~~ tsdl
typealias floating_point {
    exp_dig = 8;         /* sizeof(float) * CHAR_BIT - FLT_MANT_DIG */
    mant_dig = 24;       /* FLT_MANT_DIG */
    byte_order = native;
    align = 32;
} := float;
~~~

TODO: define NaN, +inf, -inf behavior.

Bit-packed, byte-packed or larger alignments can be used for floating
point values, similarly to integers.


#### 4.1.8 Enumerations

Enumerations are a mapping between an integer type and a table of
strings. The numerical representation of the enumeration follows the
integer type specified by the metadata. The enumeration mapping table
is detailed in the enumeration description within the metadata. The
mapping table maps inclusive value ranges (or single values) to strings.
Instead of being limited to simple `value -> string` mappings, these
enumerations map `[ start_value ... end_value ] -> string`, which map
inclusive ranges of values to strings. An enumeration from the C
language can be represented in this format by having the same
`start_value` and `end_value` for each mapping, which is in fact a
range of size 1. This single-value range is supported without repeating
the start and end values with the `value = string` declaration.
Enumerations need to contain at least one entry.

~~~ tsdl
enum name : integer_type {
    somestring          = /* start_value1 */ ... /* end_value1 */,
    "other string"      = /* start_value2 */ ... /* end_value2 */,
    yet_another_string,   /* will be assigned to end_value2 + 1 */
    "some other string" = /* value */,
    /* ... */
}
~~~

If the values are omitted, the enumeration starts at 0 and increment
of 1 for each entry. An entry with omitted value that follows a range
entry takes as value the `end_value` of the previous range + 1:

~~~ tsdl
enum name : unsigned int {
    ZERO,
    ONE,
    TWO,
    TEN = 10,
    ELEVEN,
}
~~~

Overlapping ranges within a single enumeration are implementation
defined.

A nameless enumeration can be declared as a field type or as part of
a `typedef`:

~~~ tsdl
enum : integer_type {
    /* ... */
}
~~~

Enumerations omitting the container type `: integer_type` use the `int`
type (for compatibility with C99). The `int` type _must be_ previously
declared, e.g.:

~~~ tsdl
typealias integer { size = 32; align = 32; signed = true; } := int;

enum {
    /* ... */
}
~~~

### 4.2 Compound types

Compound are aggregation of type declarations. Compound types include
structures, variant, arrays, sequences, and strings.


#### 4.2.1 Structures

Structures are aligned on the largest alignment required by basic types
contained within the structure. (This follows the ISO/C standard for
structures)

TSDL metadata representation of a named structure:

~~~ tsdl
struct name {
    field_type field_name;
    field_type field_name;
    /* ... */
};
~~~

Example:

~~~ tsdl
struct example {
    integer {                   /* nameless type */
        size = 16;
        signed = true;
        align = 16;
    } first_field_name;
    uint64_t second_field_name; /* named type declared in the metadata */
};
~~~

The fields are placed in a sequence next to each other. They each
possess a field name, which is a unique identifier within the structure.
The identifier is not allowed to use any [reserved keyword](#specC.1.2).
Replacing reserved keywords with underscore-prefixed field names is
**recommended**. Fields starting with an underscore should have their
leading underscore removed by the CTF trace readers.

A nameless structure can be declared as a field type or as part of
a `typedef`:

~~~ tsdl
struct {
    /* ... */
}
~~~

Alignment for a structure compound type can be forced to a minimum
value by adding an `align` specifier after the declaration of a
structure body. This attribute is read as: `align(value)`. The value is
specified in bits. The structure will be aligned on the maximum value
between this attribute and the alignment required by the basic types
contained within the structure. e.g.

~~~ tsdl
struct {
    /* ... */
} align(32)
~~~

#### 4.2.2 Variants (discriminated/tagged unions)

A CTF variant is a selection between different types. A CTF variant must
always be defined within the scope of a structure or within fields
contained within a structure (defined recursively). A _tag_ enumeration
field must appear in either the same static scope, prior to the variant
field (in field declaration order), in an upper static scope, or in an
upper dynamic scope (see [Static and dynamic scopes](#spec7.3.2)).
The type selection is indicated by the mapping from the enumeration
value to the string used as variant type selector. The field to use as
tag is specified by the `tag_field`, specified between `< >` after the
`variant` keyword for unnamed variants, and after _variant name_ for
named variants. It is not required that each enumeration mapping appears
as variant type tag field. It is also not required that each variant
type tag appears as enumeration mapping. However, it is required that
any enumeration mapping encountered within a stream has a matching
variant type tag field.

The alignment of the variant is the alignment of the type as selected
by the tag value for the specific instance of the variant. The size of
the variant is the size as selected by the tag value for the specific
instance of the variant.

The alignment of the type containing the variant is independent of the
variant alignment. For instance, if a structure contains two fields, a
32-bit integer, aligned on 32 bits, and a variant, which contains two
choices: either a 32-bit field, aligned on 32 bits, or a 64-bit field,
aligned on 64 bits, the alignment of the outmost structure will be
32-bit (the alignment of its largest field, disregarding the alignment
of the variant). The alignment of the variant will depend on the
selector: if the variant's 32-bit field is selected, its alignment will
be 32-bit, or 64-bit otherwise. It is important to note that variants
are specifically tailored for compactness in a stream. Therefore, the
relative offsets of compound type fields can vary depending on the
offset at which the compound type starts if it contains a variant
that itself contains a type with alignment larger than the largest field
contained within the compound type. This is caused by the fact that the
compound type may contain the enumeration that select the variant's
choice, and therefore the alignment to be applied to the compound type
cannot be determined before encountering the enumeration.

Each variant type selector possess a field name, which is a unique
identifier within the variant. The identifier is not allowed to use any
[reserved keyword](#C.1.2). Replacing reserved keywords with
underscore-prefixed field names is recommended. Fields starting with an
underscore should have their leading underscore removed by the CTF trace
readers.

A named variant declaration followed by its definition within a
structure declaration:

~~~ tsdl
variant name {
    field_type sel1;
    field_type sel2;
    field_type sel3;
    /* ... */
};

struct {
    enum : integer_type { sel1, sel2, sel3, /* ... */ } tag_field;
    /* ... */
    variant name <tag_field> v;
}
~~~

An unnamed variant definition within a structure is expressed by the
following TSDL metadata:

~~~ tsdl
struct {
    enum : integer_type { sel1, sel2, sel3, /* ... */ } tag_field;
    /* ... */
    variant <tag_field> {
        field_type sel1;
        field_type sel2;
        field_type sel3;
        /* ... */
    } v;
}
~~~

Example of a named variant within a sequence that refers to a single
tag field:

~~~ tsdl
variant example {
    uint32_t a;
    uint64_t b;
    short c;
};

struct {
    enum : uint2_t { a, b, c } choice;
    unsigned int seqlen;
    variant example <choice> v[seqlen];
}
~~~

Example of an unnamed variant:

~~~ tsdl
struct {
    enum : uint2_t { a, b, c, d } choice;

    /* Unrelated fields can be added between the variant and its tag */
    int32_t somevalue;
    variant <choice> {
        uint32_t a;
        uint64_t b;
        short c;
        struct {
            unsigned int field1;
            uint64_t field2;
        } d;
    } s;
}
~~~

Example of an unnamed variant within an array:

~~~ tsdl
struct {
    enum : uint2_t { a, b, c } choice;
    variant <choice> {
        uint32_t a;
        uint64_t b;
        short c;
    } v[10];
}
~~~

Example of a variant type definition within a structure, where the
defined type is then declared within an array of structures. This
variant refers to a tag located in an upper static scope. This example
clearly shows that a variant type definition referring to the tag `x`
uses the closest preceding field from the static scope of the type
definition.

~~~ tsdl
struct {
    enum : uint2_t { a, b, c, d } x;

    /*
     * "x" refers to the preceding "x" enumeration in the
     * static scope of the type definition.
     */
    typedef variant <x> {
      uint32_t a;
      uint64_t b;
      short c;
    } example_variant;

    struct {
      enum : int { x, y, z } x; /* This enumeration is not used by "v". */

      /* "v" uses the "enum : uint2_t { a, b, c, d }" tag. */
      example_variant v;
    } a[10];
}
~~~


#### 4.2.3 Arrays

Arrays are fixed-length. Their length is declared in the type
declaration within the metadata. They contain an array of _inner type_
elements, which can refer to any type not containing the type of the
array being declared (no circular dependency). The length is the number
of elements in an array.

TSDL metadata representation of a named array:

~~~ tsdl
typedef elem_type name[/* length */];
~~~

A nameless array can be declared as a field type within a
structure, e.g.:

~~~ tsdl
uint8_t field_name[10];
~~~

Arrays are always aligned on their element alignment requirement.


#### 4.2.4 Sequences

Sequences are dynamically-sized arrays. They refer to a _length_
unsigned integer field, which must appear in either the same static
scope, prior to the sequence field (in field declaration order),
in an upper static scope, or in an upper dynamic scope
(see [Static and dynamic scopes](#spec7.3.2)). This length field represents
the number of elements in the sequence. The sequence per se is an
array of _inner type_ elements.

TSDL metadata representation for a sequence type definition:

~~~ tsdl
struct {
    unsigned int length_field;
    typedef elem_type typename[length_field];
    typename seq_field_name;
}
~~~

A sequence can also be declared as a field type, e.g.:

~~~ tsdl
struct {
    unsigned int length_field;
    long seq_field_name[length_field];
}
~~~

Multiple sequences can refer to the same length field, and these length
fields can be in a different upper dynamic scope, e.g., assuming the
`stream.event.header` defines:

~~~ tsdl
stream {
    /* ... */
    id = 1;
    event.header := struct {
        uint16_t seq_len;
    };
};

event {
    /* ... */
    stream_id = 1;
    fields := struct {
        long seq_a[stream.event.header.seq_len];
        char seq_b[stream.event.header.seq_len];
    };
};
~~~

The sequence elements follow the [array](#spec4.2.3) specifications.


#### 4.2.5 Strings

Strings are an array of _bytes_ of variable size and are terminated by
a `'\0'` "NULL" character. Their encoding is described in the TSDL
metadata. In absence of encoding attribute information, the default
encoding is UTF-8.

TSDL metadata representation of a named string type:

~~~ tsdl
typealias string {
    encoding = /* UTF8 OR ASCII */;
} := name;
~~~

A nameless string type can be declared as a field type:

~~~ tsdl
string field_name; /* use default UTF8 encoding */
~~~

Strings are always aligned on byte size.


## 5. Event packet header

The event packet header consists of two parts: the
_event packet header_ is the same for all streams of a trace. The
second part, the _event packet context_, is described on a per-stream
basis. Both are described in the TSDL metadata.

Event packet header (all fields are optional, specified by
TSDL metadata):

  * **Magic number** (CTF magic number: 0xC1FC1FC1) specifies that this is
    a CTF packet. This magic number is optional, but when present, it
    should come at the very beginning of the packet.
  * **Trace UUID**, used to ensure the event packet match the metadata used.
    Note: we cannot use a metadata checksum in every cases instead of a
    UUID because metadata can be appended to while tracing is active.
    This field is optional.
  * **Stream ID**, used as reference to stream description in metadata.
    This field is optional if there is only one stream description in
    the metadata, but becomes required if there are more than one
    stream in the TSDL metadata description.

Event packet context (all fields are optional, specified by
TSDL metadata):

  * Event packet **content size** (in bits).
  * Event packet **size** (in bits, includes padding).
  * Event packet content checksum. Checksum excludes the event packet
    header.
  * Per-stream event **packet sequence count** (to deal with UDP packet
    loss). The number of significant sequence counter bits should also
    be present, so wrap-arounds are dealt with correctly.
  * Time-stamp at the beginning and timestamp at the end of the event
    packet. Both timestamps are written in the packet header, but
    sampled respectively while (or before) writing the first event and
    while (or after) writing the last event in the packet. The inclusive
    range between these timestamps should include all event timestamps
    assigned to events contained within the packet. The timestamp at the
    beginning of an event packet is guaranteed to be below or equal the
    timestamp at the end of that event packet. The timestamp at the end
    of an event packet is guaranteed to be below or equal the
    timestamps at the end of any following packet within the same stream.
    See [Clocks](#spec8) for more detail.
  * **Events discarded count**. Snapshot of a per-stream
    free-running counter, counting the number of events discarded that
    were supposed to be written in the stream after the last event in
    the event packet. Note: producer-consumer buffer full condition can
    fill the current event packet with padding so we know exactly where
    events have been discarded. However, if the buffer full condition
    chooses not to fill the current event packet with padding, all we
    know about the timestamp range in which the events have been
    discarded is that it is somewhere between the beginning and the end
    of the packet.
  * Lossless **compression scheme** used for the event packet content.
    Applied directly to raw data. New types of compression can be added
    in following versions of the format.
    * 0: no compression scheme
    * 1: bzip2
    * 2: gzip
    * 3: xz
  * **Cypher** used for the event packet content. Applied after
    compression.
    * 0: no encryption
    * 1: AES
  * **Checksum scheme** used for the event packet content. Applied after
    encryption.
    * 0: no checksum
    * 1: md5
    * 2: sha1
    * 3: crc32


### 5.1 Event packet header description

The event packet header layout is indicated by the
`trace.packet.header` field. Here is a recommended structure type for
the packet header with the fields typically expected (although these
fields are each optional):

~~~ tsdl
struct event_packet_header {
    uint32_t magic;
    uint8_t  uuid[16];
    uint32_t stream_id;
};

trace {
    /* ... */
    packet.header := struct event_packet_header;
};
~~~

If the magic number is not present, tools such as `file` will have no
mean to discover the file type.

If the uuid is not present, no validation that the metadata actually
corresponds to the stream is performed.

If the stream_id packet header field is missing, the trace can only
contain a single stream. Its `id` field can be left out, and its events
don't need to declare a `stream_id` field.


### 5.2 Event packet context description

Event packet context example. These are declared within the stream
declaration in the metadata. All these fields are optional. If the
packet size field is missing, the whole stream only contains a single
packet. If the content size field is missing, the packet is filled
(no padding). The content and packet sizes include all headers.

An example event packet context type:

~~~ tsdl
struct event_packet_context {
    uint64_t timestamp_begin;
    uint64_t timestamp_end;
    uint32_t checksum;
    uint32_t stream_packet_count;
    uint32_t events_discarded;
    uint32_t cpu_id;
    uint64_t content_size;
    uint64_t packet_size;
    uint8_t  compression_scheme;
    uint8_t  encryption_scheme;
    uint8_t  checksum_scheme;
};
~~~


## 6. Event Structure

The overall structure of an event is:

  1. Event header (as specified by the stream metadata)
  2. Stream event context (as specified by the stream metadata)
  3. Event context (as specified by the event metadata)
  4. Event payload (as specified by the event metadata)

This structure defines an implicit dynamic scoping, where variants
located in inner structures (those with a higher number in the listing
above) can refer to the fields of outer structures (with lower number
in the listing above). See [TSDL scopes](#spec7.3) for more detail.

The total length of an event is defined as the difference between the
end of its event payload and the end of the previous event's event
payload. Therefore, it includes the event header alignment padding, and
all its fields and their respective alignment padding. Events of length
0 are forbidden.


### 6.1 Event header

Event headers can be described within the metadata. We hereby propose,
as an example, two types of events headers. Type 1 accommodates streams
with less than 31 event IDs. Type 2 accommodates streams with 31 or
more event IDs.

One major factor can vary between streams: the number of event IDs
assigned to a stream. Luckily, this information tends to stay
relatively constant (modulo event registration while trace is being
recorded), so we can specify different representations for streams
containing few event IDs and streams containing many event IDs, so we
end up representing the event ID and timestamp as densely as possible
in each case.

The header is extended in the rare occasions where the information
cannot be represented in the ranges available in the standard event
header. They are also used in the rare occasions where the data
required for a field could not be collected: the flag corresponding to
the missing field within the `missing_fields` array is then set to 1.

Types `uintX_t` represent an `X`-bit unsigned integer, as declared with
either:

~~~ tsdl
typealias integer {
    size = /* X */;
    align = /* X */;
    signed = false;
} := uintX_t;
~~~

or

~~~ tsdl
typealias integer {
    size = /* X */;
    align = 1;
    signed = false;
} := uintX_t;
~~~

For more information about timestamp fields, see [Clocks](#spec8).


#### 6.1.1 Type 1: few event IDs

  * Aligned on 32-bit (or 8-bit if byte-packed, depending on the
    architecture preference)
  * Native architecture byte ordering
  * For `compact` selection, fixed size of 32 bits
  * For "extended" selection, size depends on the architecture and
    variant alignment

~~~ tsdl
struct event_header_1 {
    /*
     * id: range: 0 - 30.
     * id 31 is reserved to indicate an extended header.
     */
    enum : uint5_t { compact = 0 ... 30, extended = 31 } id;
    variant <id> {
        struct {
            uint27_t timestamp;
        } compact;
        struct {
            uint32_t id;        /* 32-bit event IDs */
            uint64_t timestamp; /* 64-bit timestamps */
        } extended;
    } v;
} align(32); /* or align(8) */
~~~


#### 6.1.2 Type 2: many event IDs

  * Aligned on 16-bit (or 8-bit if byte-packed, depending on the
    architecture preference)
  * Native architecture byte ordering
  * For `compact` selection, size depends on the architecture and
    variant alignment
  * For `extended` selection, size depends on the architecture and
    variant alignment

~~~ tsdl
struct event_header_2 {
    /*
     * id: range: 0 - 65534.
     * id 65535 is reserved to indicate an extended header.
     */
    enum : uint16_t { compact = 0 ... 65534, extended = 65535 } id;
    variant <id> {
        struct {
            uint32_t timestamp;
        } compact;
        struct {
            uint32_t id;        /* 32-bit event IDs */
            uint64_t timestamp; /* 64-bit timestamps */
        } extended;
    } v;
} align(16); /* or align(8) */
~~~


### 6.2 Stream event context and event context

The event context contains information relative to the current event.
The choice and meaning of this information is specified by the TSDL
stream and event metadata descriptions. The stream context is applied
to all events within the stream. The stream context structure follows
the event header. The event context is applied to specific events. Its
structure follows the stream context structure.

An example of stream-level event context is to save the event payload
size with each event, or to save the current PID with each event.
These are declared within the stream declaration within the metadata:

~~~ tsdl
stream {
    /* ... */
    event.context := struct {
        uint pid;
        uint16_t payload_size;
    };
};
~~~

An example of event-specific event context is to declare a bitmap of
missing fields, only appended after the stream event context if the
extended event header is selected. `NR_FIELDS` is the number of fields
within the event (a numeric value).

~~~ tsdl
event {
    context := struct {
        variant <id> {
            struct { } compact;
            struct {
                /* missing event fields bitmap */
                uint1_t missing_fields[NR_FIELDS];
            } extended;
        } v;
    };
    /* ... */
}
~~~


### 6.3 Event payload

An event payload contains fields specific to a given event type. The
fields belonging to an event type are described in the event-specific
metadata within a structure type.


#### 6.3.1 Padding

No padding at the end of the event payload. This differs from the ISO/C
standard for structures, but follows the CTF standard for structures.
In a trace, even though it makes sense to align the beginning of a
structure, it really makes no sense to add padding at the end of the
structure, because structures are usually not followed by a structure
of the same type.

This trick can be done by adding a zero-length `end` field at the end
of the C structures, and by using the offset of this field rather than
using `sizeof()` when calculating the size of a structure
(see [Helper macros](#specA)).


#### 6.3.2 Alignment

The event payload is aligned on the largest alignment required by types
contained within the payload. This follows the ISO/C standard for
structures.


## 7. Trace Stream Description Language (TSDL)

The Trace Stream Description Language (TSDL) allows expression of the
binary trace streams layout in a C99-like Domain Specific Language
(DSL).


### 7.1 Meta-data

The trace stream layout description is located in the trace metadata.
The metadata is itself located in a stream identified by its name:
`metadata`.

The metadata description can be expressed in two different formats:
text-only and packet-based. The text-only description facilitates
generation of metadata and provides a convenient way to enter the
metadata information by hand. The packet-based metadata provides the
CTF stream packet facilities (checksumming, compression, encryption,
network-readiness) for metadata stream generated and transported by a
tracer.

The text-only metadata file is a plain-text TSDL description. This file
must begin with the following characters to identify the file as a CTF
TSDL text-based metadata file (without the double-quotes):

~~~ text
"/* CTF"
~~~

It must be followed by a space, and the version of the specification
followed by the CTF trace, e.g.:

~~~ text
" 1.8"
~~~

These characters allow automated discovery of file type and CTF
specification version. They are interpreted as a the beginning of a
comment by the TSDL metadata parser. The comment can be continued to
contain extra commented characters before it is closed.

The packet-based metadata is made of _metadata packets_, which each
start with a metadata packet header. The packet-based metadata
description is detected by reading the magic number 0x75D11D57 at the
beginning of the file. This magic number is also used to detect the
endianness of the architecture by trying to read the CTF magic number
and its counterpart in reversed endianness. The events within the
metadata stream have no event header nor event context. Each event only
contains a special _sequence_ payload, which is a sequence of bits which
length is implicitly calculated by using the
`trace.packet.header.content_size` field, minus the packet header size.
The formatting of this sequence of bits is a plain-text representation
of the TSDL description. Each metadata packet start with a special
packet header, specific to the metadata stream, which contains,
exactly:

~~~ tsdl
struct metadata_packet_header {
    uint32_t magic;              /* 0x75D11D57 */
    uint8_t  uuid[16];           /* Unique Universal Identifier */
    uint32_t checksum;           /* 0 if unused */
    uint32_t content_size;       /* in bits */
    uint32_t packet_size;        /* in bits */
    uint8_t  compression_scheme; /* 0 if unused */
    uint8_t  encryption_scheme;  /* 0 if unused */
    uint8_t  checksum_scheme;    /* 0 if unused */
    uint8_t  major;              /* CTF spec version major number */
    uint8_t  minor;              /* CTF spec version minor number */
};
~~~

The packet-based metadata can be converted to a text-only metadata by
concatenating all the strings it contains.

In the textual representation of the metadata, the text contained
within `/*` and `*/`, as well as within `//` and end of line, are
treated as comments. Boolean values can be represented as `true`,
`TRUE`, or `1` for true, and `false`, `FALSE`, or `0` for false. Within
the string-based metadata description, the trace UUID is represented as
a string of hexadecimal digits and dashes `-`. In the event packet
header, the trace UUID is represented as an array of bytes.


### 7.2 Declaration vs definition

A declaration associates a layout to a type, without specifying where
this type is located in the event [structure hierarchy](#spec6).
This therefore includes `typedef`, `typealias`, as well as all type
specifiers. In certain circumstances (`typedef`, structure field and
variant field), a declaration is followed by a declarator, which specify
the newly defined type name (for `typedef`), or the field name (for
declarations located within structure and variants). Array and sequence,
declared with square brackets (`[` `]`), are part of the declarator,
similarly to C99. The enumeration base type is specified by
`: enum_base`, which is part of the type specifier. The variant tag
name, specified between `<` `>`, is also part of the type specifier.

A definition associates a type to a location in the event
[structure hierarchy](#spec6). This association is denoted by `:=`,
as shown in [TSDL scopes](#spec7.3).


### 7.3 TSDL scopes

TSDL uses three different types of scoping: a lexical scope is used for
declarations and type definitions, and static and dynamic scopes are
used for variants references to tag fields (with relative and absolute
path lookups) and for sequence references to length fields.


#### 7.3.1 Lexical Scope

Each of `trace`, `env`, `stream`, `event`, `struct` and `variant` have
their own nestable declaration scope, within which types can be declared
using `typedef` and `typealias`. A root declaration scope also contains
all declarations located outside of any of the aforementioned
declarations. An inner declaration scope can refer to type declared
within its container lexical scope prior to the inner declaration scope.
Redefinition of a typedef or typealias is not valid, although hiding an
upper scope typedef or typealias is allowed within a sub-scope.


#### 7.3.2 Static and dynamic scopes

A local static scope consists in the scope generated by the declaration
of fields within a compound type. A static scope is a local static scope
augmented with the nested sub-static-scopes it contains.

A dynamic scope consists in the static scope augmented with the
implicit [event structure](#spec6) definition hierarchy.

Multiple declarations of the same field name within a local static scope
is not valid. It is however valid to re-use the same field name in
different local scopes.

Nested static and dynamic scopes form lookup paths. These are used for
variant tag and sequence length references. They are used at the variant
and sequence definition site to look up the location of the tag field
associated with a variant, and to lookup up the location of the length
field associated with a sequence.

Variants and sequences can refer to a tag field either using a relative
path or an absolute path. The relative path is relative to the scope in
which the variant or sequence performing the lookup is located.
Relative paths are only allowed to lookup within the same static scope,
which includes its nested static scopes. Lookups targeting parent static
scopes need to be performed with an absolute path.

Absolute path lookups use the full path including the dynamic scope
followed by a `.` and then the static scope. Therefore, variants (or
sequences) in lower levels in the dynamic scope (e.g., event context)
can refer to a tag (or length) field located in upper levels
(e.g., in the event header) by specifying, in this case, the associated
tag with `<stream.event.header.field_name>`. This allows, for instance,
the event context to define a variant referring to the `id` field of
the event header as selector.

The dynamic scope prefixes are thus:

  * Trace environment: `<env. >`
  * Trace packet header: `<trace.packet.header. >`
  * Stream packet context: `<stream.packet.context. >`
  * Event header: `<stream.event.header. >`
  * Stream event context: `<stream.event.context. >`
  * Event context: `<event.context. >`
  * Event payload: `<event.fields. >`

The target dynamic scope must be specified explicitly when referring to
a field outside of the static scope (absolute scope reference). No
conflict can occur between relative and dynamic paths, because the
keywords `trace`, `stream`, and `event` are reserved, and thus not
permitted as field names. It is recommended that field names clashing
with CTF and C99 reserved keywords use an underscore prefix to
eliminate the risk of generating a description containing an invalid
field name. Consequently, fields starting with an underscore should have
their leading underscore removed by the CTF trace readers.

The information available in the dynamic scopes can be thought of as the
current tracing context. At trace production, information about the
current context is saved into the specified scope field levels. At trace
consumption, for each event, the current trace context is therefore
readable by accessing the upper dynamic scopes.


### 7.4 TSDL examples

The grammar representing the TSDL metadata is presented in
[TSDL grammar](#specC). This section presents a rather lighter reading that
consists in examples of TSDL metadata, with template values.

The stream ID can be left out if there is only one stream in the
trace. The event `id` field can be left out if there is only one event
in a stream.

~~~ tsdl
trace {
    major = /* value */;            /* CTF spec version major number */
    minor = /* value */;            /* CTF spec version minor number */
    uuid = "aaaaaaaa-aaaa-aaaa-aaaa-aaaaaaaaaaaa";  /* Trace UUID */
    byte_order = /* be OR le */;    /* Endianness (required) */
    packet.header := struct {
        uint32_t magic;
        uint8_t  uuid[16];
        uint32_t stream_id;
    };
};

/*
 * The "env" (environment) scope contains assignment expressions. The
 * field names and content are implementation-defined.
 */
env {
    pid = /* value */;    /* example */
    proc_name = "name";   /* example */
    /* ... */
};

stream {
    id = /* stream_id */;
    /* Type 1 - Few event IDs; Type 2 - Many event IDs. See section 6.1. */
    event.header := /* event_header_1 OR event_header_2 */;
    event.context := struct {
        /* ... */
    };
    packet.context := struct {
        /* ... */
    };
};

event {
    name = "event_name";
    id = /* value */;            /* Numeric identifier within the stream */
    stream_id = /* stream_id */;
    loglevel = /* value */;
    model.emf.uri = "string";
    context := struct {
        /* ... */
    };
    fields := struct {
        /* ... */
    };
};

callsite {
    name = "event_name";
    func = "func_name";
    file = "myfile.c";
    line = 39;
    ip = 0x40096c;
};
~~~

More detail on [types](#spec4):

~~~ tsdl
/*
 * Named types:
 *
 * Type declarations behave similarly to the C standard.
 */

typedef aliased_type_specifiers new_type_declarators;

/* e.g.: typedef struct example new_type_name[10]; */

/*
 * typealias
 *
 * The "typealias" declaration can be used to give a name (including
 * pointer declarator specifier) to a type. It should also be used to
 * map basic C types (float, int, unsigned long, ...) to a CTF type.
 * Typealias is a superset of "typedef": it also allows assignment of a
 * simple variable identifier to a type.
 */

typealias type_class {
    /* ... */
} := type_specifiers type_declarator;

/*
 * e.g.:
 * typealias integer {
 *   size = 32;
 *   align = 32;
 *   signed = false;
 * } := struct page *;
 *
 * typealias integer {
 *  size = 32;
 *  align = 32;
 *  signed = true;
 * } := int;
 */

struct name {
    /* ... */
};

variant name {
    /* ... */
};

enum name : integer_type {
    /* ... */
};
~~~

Unnamed types, contained within compound type fields, `typedef` or
`typealias`:

~~~ tsdl
struct {
    /* ... */
}
~~~

~~~ tsdl
struct {
    /* ... */
} align(value)
~~~

~~~ tsdl
variant {
    /* ... */
}
~~~

~~~ tsdl
enum : integer_type {
    /* ... */
}
~~~

~~~ tsdl
typedef type new_type[length];

struct {
    type field_name[length];
}
~~~

~~~ tsdl
typedef type new_type[length_type];

struct {
    type field_name[length_type];
}
~~~

~~~ tsdl
integer {
    /* ... */
}
~~~

~~~ tsdl
floating_point {
    /* ... */
}
~~~

~~~ tsdl
struct {
    integer_type field_name:size;   /* GNU/C bitfield */
}
~~~

~~~ tsdl
struct {
    string field_name;
}
~~~


## 8. Clocks

Clock metadata allows to describe the clock topology of the system, as
well as to detail each clock parameter. In absence of clock description,
it is assumed that all fields named `timestamp` use the same clock
source, which increments once per nanosecond.

Describing a clock and how it is used by streams is threefold: first,
the clock and clock topology should be described in a `clock`
description block, e.g.:

~~~ tsdl
clock {
    name = cycle_counter_sync;
    uuid = "62189bee-96dc-11e0-91a8-cfa3d89f3923";
    description = "Cycle counter synchronized across CPUs";
    freq = 1000000000;           /* frequency, in Hz */
    /* precision in seconds is: 1000 * (1/freq) */
    precision = 1000;
    /*
     * clock value offset from Epoch is:
     * offset_s + (offset * (1/freq))
     */
    offset_s = 1326476837;
    offset = 897235420;
    absolute = FALSE;
};
~~~

The mandatory `name` field specifies the name of the clock identifier,
which can later be used as a reference. The optional field `uuid` is
the unique identifier of the clock. It can be used to correlate
different traces that use the same clock. An optional textual
description string can be added with the `description` field. The
`freq` field is the initial frequency of the clock, in Hz. If the
`freq` field is not present, the frequency is assumed to be 1000000000
(providing clock increment of 1 ns). The optional `precision` field
details the uncertainty on the clock measurements, in (1/freq) units.
The `offset_s` and `offset` fields indicate the offset from
POSIX.1 Epoch, 1970-01-01 00:00:00 +0000 (UTC), to the zero of value
of the clock. The `offset_s` field is in seconds. The `offset` field is
in (1/freq) units. If any of the `offset_s` or `offset` field is not
present, it is assigned the 0 value. The field `absolute` is `TRUE` if
the clock is a global reference across different clock UUID
(e.g. NTP time). Otherwise, `absolute` is `FALSE`, and the clock can
be considered as synchronized only with other clocks that have the same
UUID.

Secondly, a reference to this clock should be added within an integer
type:

~~~ tsdl
typealias integer {
    size = 64; align = 1; signed = false;
    map = clock.cycle_counter_sync.value;
} := uint64_ccnt_t;
~~~

Thirdly, stream declarations can reference the clock they use as a
timestamp source:

~~~ tsdl
struct packet_context {
    uint64_ccnt_t ccnt_begin;
    uint64_ccnt_t ccnt_end;
    /* ... */
};

stream {
    /* ... */
    event.header := struct {
        uint64_ccnt_t timestamp;
        /* ... */
    };
    packet.context := struct packet_context;
};
~~~

For a N-bit integer type referring to a clock, if the integer overflows
compared to the N low order bits of the clock prior value found in the
same stream, then it is assumed that one, and only one, overflow
occurred. It is therefore important that events encoding time on a small
number of bits happen frequently enough to detect when more than one
N-bit overflow occurs.

In a packet context, clock field names ending with `_begin` and `_end`
have a special meaning: this refers to the timestamps at, respectively,
the beginning and the end of each packet.


## A. Helper macros

The two following macros keep track of the size of a GNU/C structure
without padding at the end by placing HEADER_END as the last field.
A one byte end field is used for C90 compatibility (C99 flexible arrays
could be used here). Note that this does not affect the effective
structure size, which should always be calculated with the
`header_sizeof()` helper.

~~~ c
#define HEADER_END          char end_field
#define header_sizeof(type) offsetof(typeof(type), end_field)
~~~

## B. Stream header rationale

An event stream is divided in contiguous event packets of variable
size. These subdivisions allow the trace analyzer to perform a fast
binary search by time within the stream (typically requiring to index
only the event packet headers) without reading the whole stream. These
subdivisions have a variable size to eliminate the need to transfer the
event packet padding when partially filled event packets must be sent
when streaming a trace for live viewing/analysis. An event packet can
contain a certain amount of padding at the end. Dividing streams into
event packets is also useful for network streaming over UDP and flight
recorder mode tracing (a whole event packet can be swapped out of the
buffer atomically for reading).

The stream header is repeated at the beginning of each event packet to
allow flexibility in terms of:

  * streaming support
  * allowing arbitrary buffers to be discarded without making the trace
    unreadable
  * allow UDP packet loss handling by either dealing with missing event packet
    or asking for re-transmission
  * transparently support flight recorder mode
  * transparently support crash dump


## C. TSDL Grammar

~~~ c
/*
 * Common Trace Format (CTF) Trace Stream Description Language (TSDL) Grammar.
 *
 * Inspired from the C99 grammar:
 * http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1124.pdf (Annex A)
 * and c++1x grammar (draft)
 * http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2011/n3291.pdf (Annex A)
 *
 * Specialized for CTF needs by including only constant and declarations from
 * C99 (excluding function declarations), and by adding support for variants,
 * sequences and CTF-specific specifiers. Enumeration container types
 * semantic is inspired from c++1x enum-base.
 */
~~~


### C.1 Lexical grammar


#### C.1.1 Lexical elements

~~~ text
token:
    keyword
    identifier
    constant
    string-literal
    punctuator
~~~

#### C.1.2 Keywords

~~~ text
keyword: is one of

align
callsite
const
char
clock
double
enum
env
event
floating_point
float
integer
int
long
short
signed
stream
string
struct
trace
typealias
typedef
unsigned
variant
void
_Bool
_Complex
_Imaginary
~~~


#### C.1.3 Identifiers

~~~ text
identifier:
    identifier-nondigit
    identifier identifier-nondigit
    identifier digit

identifier-nondigit:
    nondigit
    universal-character-name
    any other implementation-defined characters

nondigit:
    _
    [a-zA-Z]    /* regular expression */

digit:
    [0-9]        /* regular expression */
~~~


#### C.1.4 Universal character names

~~~ text
universal-character-name:
    \u hex-quad
    \U hex-quad hex-quad

hex-quad:
    hexadecimal-digit hexadecimal-digit hexadecimal-digit hexadecimal-digit
~~~


##### C.1.5 Constants

~~~ text
constant:
    integer-constant
    enumeration-constant
    character-constant

integer-constant:
    decimal-constant integer-suffix-opt
    octal-constant integer-suffix-opt
    hexadecimal-constant integer-suffix-opt

decimal-constant:
    nonzero-digit
    decimal-constant digit

octal-constant:
    0
    octal-constant octal-digit

hexadecimal-constant:
    hexadecimal-prefix hexadecimal-digit
    hexadecimal-constant hexadecimal-digit

hexadecimal-prefix:
    0x
    0X

nonzero-digit:
    [1-9]

integer-suffix:
    unsigned-suffix long-suffix-opt
    unsigned-suffix long-long-suffix
    long-suffix unsigned-suffix-opt
    long-long-suffix unsigned-suffix-opt

unsigned-suffix:
    u
    U

long-suffix:
    l
    L

long-long-suffix:
    ll
    LL

enumeration-constant:
    identifier
    string-literal

character-constant:
    ' c-char-sequence '
    L' c-char-sequence '

c-char-sequence:
    c-char
    c-char-sequence c-char

c-char:
    any member of source charset except single-quote ('), backslash
    (\), or new-line character.
    escape-sequence

escape-sequence:
    simple-escape-sequence
    octal-escape-sequence
    hexadecimal-escape-sequence
    universal-character-name

simple-escape-sequence: one of
    \' \" \? \\ \a \b \f \n \r \t \v

octal-escape-sequence:
    \ octal-digit
    \ octal-digit octal-digit
    \ octal-digit octal-digit octal-digit

hexadecimal-escape-sequence:
    \x hexadecimal-digit
    hexadecimal-escape-sequence hexadecimal-digit
~~~


#### C.1.6 String literals

~~~ text
string-literal:
    " s-char-sequence-opt "
    L" s-char-sequence-opt "

s-char-sequence:
    s-char
    s-char-sequence s-char

s-char:
    any member of source charset except double-quote ("), backslash
    (\), or new-line character.
    escape-sequence
~~~


#### C.1.7 Punctuators

~~~ text
punctuator: one of
    [ ] ( ) { } . -> * + - < > : ; ... = ,
~~~


### C.2 Phrase structure grammar

~~~ text
primary-expression:
    identifier
    constant
    string-literal
    ( unary-expression )

postfix-expression:
    primary-expression
    postfix-expression [ unary-expression ]
    postfix-expression . identifier
    postfix-expressoin -> identifier

unary-expression:
    postfix-expression
    unary-operator postfix-expression

unary-operator: one of
    + -

assignment-operator:
    =

type-assignment-operator:
    :=

constant-expression-range:
    unary-expression ... unary-expression
~~~


#### C.2.2 Declarations:

~~~ text
declaration:
    declaration-specifiers declarator-list-opt ;
    ctf-specifier ;

declaration-specifiers:
    storage-class-specifier declaration-specifiers-opt
    type-specifier declaration-specifiers-opt
    type-qualifier declaration-specifiers-opt

declarator-list:
    declarator
    declarator-list , declarator

abstract-declarator-list:
    abstract-declarator
    abstract-declarator-list , abstract-declarator

storage-class-specifier:
    typedef

type-specifier:
    void
    char
    short
    int
    long
    float
    double
    signed
    unsigned
    _Bool
    _Complex
    _Imaginary
    struct-specifier
    variant-specifier
    enum-specifier
    typedef-name
    ctf-type-specifier

align-attribute:
    align ( unary-expression )

struct-specifier:
    struct identifier-opt { struct-or-variant-declaration-list-opt } align-attribute-opt
    struct identifier align-attribute-opt

struct-or-variant-declaration-list:
    struct-or-variant-declaration
    struct-or-variant-declaration-list struct-or-variant-declaration

struct-or-variant-declaration:
    specifier-qualifier-list struct-or-variant-declarator-list ;
    declaration-specifiers-opt storage-class-specifier declaration-specifiers-opt declarator-list ;
    typealias declaration-specifiers abstract-declarator-list type-assignment-operator declaration-specifiers abstract-declarator-list ;
    typealias declaration-specifiers abstract-declarator-list type-assignment-operator declarator-list ;

specifier-qualifier-list:
    type-specifier specifier-qualifier-list-opt
    type-qualifier specifier-qualifier-list-opt

struct-or-variant-declarator-list:
    struct-or-variant-declarator
    struct-or-variant-declarator-list , struct-or-variant-declarator

struct-or-variant-declarator:
    declarator
    declarator-opt : unary-expression

variant-specifier:
    variant identifier-opt variant-tag-opt { struct-or-variant-declaration-list }
    variant identifier variant-tag

variant-tag:
    < unary-expression >

enum-specifier:
    enum identifier-opt { enumerator-list }
    enum identifier-opt { enumerator-list , }
    enum identifier
    enum identifier-opt : declaration-specifiers { enumerator-list }
    enum identifier-opt : declaration-specifiers { enumerator-list , }

enumerator-list:
    enumerator
    enumerator-list , enumerator

enumerator:
    enumeration-constant
    enumeration-constant assignment-operator unary-expression
    enumeration-constant assignment-operator constant-expression-range

type-qualifier:
    const

declarator:
    pointer-opt direct-declarator

direct-declarator:
    identifier
    ( declarator )
    direct-declarator [ unary-expression ]

abstract-declarator:
    pointer-opt direct-abstract-declarator

direct-abstract-declarator:
    identifier-opt
    ( abstract-declarator )
    direct-abstract-declarator [ unary-expression ]
    direct-abstract-declarator [ ]

pointer:
    * type-qualifier-list-opt
    * type-qualifier-list-opt pointer

type-qualifier-list:
    type-qualifier
    type-qualifier-list type-qualifier

typedef-name:
    identifier
~~~


#### C.2.3 CTF-specific declarations

~~~ text
ctf-specifier:
    clock { ctf-assignment-expression-list-opt }
    event { ctf-assignment-expression-list-opt }
    stream { ctf-assignment-expression-list-opt }
    env { ctf-assignment-expression-list-opt }
    trace { ctf-assignment-expression-list-opt }
    callsite { ctf-assignment-expression-list-opt }
    typealias declaration-specifiers abstract-declarator-list type-assignment-operator declaration-specifiers abstract-declarator-list
    typealias declaration-specifiers abstract-declarator-list type-assignment-operator declarator-list

ctf-type-specifier:
    floating_point { ctf-assignment-expression-list-opt }
    integer { ctf-assignment-expression-list-opt }
    string { ctf-assignment-expression-list-opt }
    string

ctf-assignment-expression-list:
    ctf-assignment-expression ;
    ctf-assignment-expression-list ctf-assignment-expression ;

ctf-assignment-expression:
    unary-expression assignment-operator unary-expression
    unary-expression type-assignment-operator type-specifier
    declaration-specifiers-opt storage-class-specifier declaration-specifiers-opt declarator-list
    typealias declaration-specifiers abstract-declarator-list type-assignment-operator declaration-specifiers abstract-declarator-list
    typealias declaration-specifiers abstract-declarator-list type-assignment-operator declarator-list
~~~