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+# 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
+~~~