RFC: Common Trace Format (CTF) Proposal (pre-v1.7) Mathieu Desnoyers, EfficiOS Inc. The goal of the present document is to propose 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) 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 tree: 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 project, a converter between trace formats. The development tree is available at: git tree: git://git.efficios.com/babeltrace.git gitweb: http://git.efficios.com/?p=babeltrace.git 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. (aka: 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 separate file for output. Therefore, a stored trace can be represented as a directory containing one file per stream. A metadata event stream contains information on trace event types expressed in the Trace Stream Description Language (TSDL). It describes: - Trace version. - Types available. - Per-stream event header description. - Per-stream event header selection. - Per-stream event context fields. - Per-event - Event type to stream mapping. - Event type to name mapping. - Event type to ID mapping. - Event fields description. 3. Event stream An event stream is divided in contiguous event packets of variable size. These subdivisions have a 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 Appendix B. Stream Header Rationale. 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 class below ("Integers" section). 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" section. All basic types, except bitfields, are either aligned on an architecture-defined specific alignment or byte-packed, depending on the architecture preference. 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 types are byte-packed. Metadata attribute representation of a specific alignment: align = value; /* value in bits */ 4.1.3 Byte order By default, the native endianness of the source architecture the trace is used. Byte order can be overridden for a basic type by specifying a "byte_order" attribute. 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. If not specified, the byte order is native. Metadata representation: byte_order = native OR network OR be OR le; /* network and be are aliases */ 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. Metadata representation: size = value; (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 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. A MIT-licensed reference implementation of the CTF portable bitfields is available at: 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 explicitely added (see 4.1.6 GNU/C bitfields) to follow the GCC layout if needed. Metadata representation: integer { signed = true OR false; /* default false */ byte_order = native OR network OR be OR le; /* default native */ size = value; /* value in bits, no default */ align = value; /* value in bits */ } Example of type inheritance (creation of a uint32_t named type): typealias integer { size = 32; signed = false; align = 32; } := uint32_t; Definition of a named 5-bit signed bitfield: typealias integer { size = 5; signed = true; align = 1; } := int5_t; 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". Metadata representation: unit_type name:size: As an example, the following structure declared in C compiled by GCC: 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 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 . - 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 Metadata representation: floating_point { exp_dig = value; mant_dig = value; byte_order = native OR network OR be OR le; } Example of type inheritance: typealias floating_point { exp_dig = 8; /* sizeof(float) * CHAR_BIT - FLT_MANT_DIG */ mant_dig = 24; /* FLT_MANT_DIG */ byte_order = native; } := float; TODO: define NaN, +inf, -inf behavior. 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 element, 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. 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: 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: 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.: 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) Metadata representation of a named structure: struct name { field_type field_name; field_type field_name; ... }; Example: 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. A nameless structure can be declared as a field type or as part of a typedef: struct { ... } 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 lexical scope, prior to the variant field (in field declaration order), in an uppermost lexical scope (see Section 7.3.1), or in an uppermost dynamic scope (see Section 7.3.2). 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. 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 alignment of the type containing the variant is independent of the variant alignment. The size of the variant is the size as selected by the tag value for the specific instance of the variant. A named variant declaration followed by its definition within a structure declaration: variant name { field_type sel1; field_type sel2; field_type sel3; ... }; struct { enum : integer_type { sel1, sel2, sel3, ... } tag_field; ... variant name v; } An unnamed variant definition within a structure is expressed by the following metadata: struct { enum : integer_type { sel1, sel2, sel3, ... } tag_field; ... variant { 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: variant example { uint32_t a; uint64_t b; short c; }; struct { enum : uint2_t { a, b, c } choice; variant example v[unsigned int]; } Example of an unnamed variant: struct { enum : uint2_t { a, b, c, d } choice; /* Unrelated fields can be added between the variant and its tag */ int32_t somevalue; variant { 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: struct { enum : uint2_t { a, b, c } choice; variant { 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 lexical scope. This example clearly shows that a variant type definition referring to the tag "x" uses the closest preceding field from the lexical scope of the type definition. struct { enum : uint2_t { a, b, c, d } x; typedef variant { /* * "x" refers to the preceding "x" enumeration in the * lexical scope of the type definition. */ uint32_t a; uint64_t b; short c; } example_variant; struct { enum : int { x, y, z } x; /* This enumeration is not used by "v". */ example_variant v; /* * "v" uses the "enum : uint2_t { a, b, c, d }" * tag. */ } 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. Metadata representation of a named array: typedef elem_type name[length]; A nameless array can be declared as a field type within a structure, e.g.: uint8_t field_name[10]; 4.2.4 Sequences Sequences are dynamically-sized arrays. They start with an integer that specify the length of the sequence, followed by an array of "inner type" elements. The length is the number of elements in the sequence. Metadata representation for a named sequence: typedef elem_type name[length_type]; A nameless sequence can be declared as a field type, e.g.: long field_name[int]; The length type follows the integer types specifications, and the sequence elements follow the "array" 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 metadata. In absence of encoding attribute information, the default encoding is UTF-8. Metadata representation of a named string type: typealias string { encoding = UTF8 OR ASCII; } := name; A nameless string type can be declared as a field type: string field_name; /* Use default UTF8 encoding */ 5. Event Packet Header The event packet header consists of two part: one is mandatory and have a fixed layout. The second part, the "event packet context", has its layout described in the metadata. - Aligned on page size. Fixed size. Fields either aligned or packed (depending on the architecture preference). No padding at the end of the event packet header. Native architecture byte ordering. Fixed layout (event packet header): - Magic number (CTF magic numbers: 0xC1FC1FC1 and its reverse endianness representation: 0xC11FFCC1) It needs to have a non-symmetric bytewise representation. Used to distinguish between big and little endian traces (this information is determined by knowing the endianness of the architecture reading the trace and comparing the magic number against its value and the reverse, 0xC11FFCC1). This magic number specifies that we use the CTF metadata description language described in this document. Different magic numbers should be used for other metadata description languages. - Trace UUID, used to ensure the event packet match the metadata used. (note: we cannot use a metadata checksum because metadata can be appended to while tracing is active) - Stream ID, used as reference to stream description in metadata. Metadata-defined layout (event packet context): - Event packet content size (in bytes). - Event packet size (in bytes, includes padding). - Event packet content checksum (optional). 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 deal with correctly. - Timestamp 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. - 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 prior to the first event in the event packet. * Note: producer-consumer buffer full condition should fill the current event packet with padding so we know exactly where events have been discarded. - 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 Fixed Layout Description The event packet header layout is indicated by the trace packet.header field. Here is an example structure type for the packet header with the fields typically expected: struct event_packet_header { uint32_t magic; uint8_t trace_uuid[16]; uint32_t stream_id; }; trace { ... packet.header := struct event_packet_header; }; If a packet header lacks the "magic" number field, the trace endianness needs to be specified in the trace "endian" metadata attribute. If the trace_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 except for "content_size" and "packet_size", which must be present in the context. An example event packet context type: 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; uint32_t/uint16_t content_size; uint32_t/uint16_t packet_size; uint8_t stream_packet_count_bits; /* Significant counter bits */ uint8_t compression_scheme; uint8_t encryption_scheme; uint8_t checksum_scheme; }; 6. Event Structure The overall structure of an event is: 1 - Stream Packet Context (as specified by the stream metadata) 2 - Event Header (as specified by the stream metadata) 3 - Stream Event Context (as specified by the stream metadata) 4 - Event Context (as specified by the event metadata) 5 - 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 Section 7.3 TSDL Scopes for more detail. 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. 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: 32 bits. - For "extended" selection - Size depends on the architecture and variant alignment. 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 { struct { uint27_t timestamp; } compact; struct { uint32_t id; /* 32-bit event IDs */ uint64_t timestamp; /* 64-bit timestamps */ } extended; } v; }; 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. 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 { struct { uint32_t timestamp; } compact; struct { uint32_t id; /* 32-bit event IDs */ uint64_t timestamp; /* 64-bit timestamps */ } extended; } v; }; 6.2 Event Context The event context contains information relative to the current event. The choice and meaning of this information is specified by the metadata "stream" and "event" information. 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 stucture. 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: 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). event { context = struct { variant { struct { } compact; struct { uint1_t missing_fields[NR_FIELDS]; /* missing event fields bitmap */ } 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 Appendix "A. Helper macros"). 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 Metadata The trace stream layout description is located in the trace meta-data. The meta-data is itself located in a stream identified by its name: "metadata". It is made of "event packets", which each start with an event packet header. The event type within the metadata stream have no event header nor event context. Each event only contains a "string" payload without any null-character. The events are packed one next to another. Each event packet start with an event packet header, which contains, amongst other fields, the magic number, trace UUID and packet length. In the event packet header, the trace UUID is represented as an array of bytes. Within the string-based metadata description, the trace UUID is represented as a string of hexadecimal digits and dashes "-". The metadata can be parsed by reading characters within the metadata stream, for each packet starting after the packet header, for the length of the packet payload specified in the header. 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. 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 (see Section 6). 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 (see Section 6). This association is denoted by ":=", as shown in Section 7.3. 7.3 TSDL Scopes TSDL uses two different types of scoping: a lexical scope is used for declarations and type definitions, and a dynamic scope is used for variants references to tag fields. 7.3.1 Lexical Scope Each of "trace", "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 Dynamic Scope A dynamic scope consists in the lexical scope augmented with the implicit event structure definition hierarchy presented at Section 6. The dynamic scope is only used for variant tag definitions. It is used at definition time to look up the location of the tag field associated with a variant. Therefore, variants in lower levels in the dynamic scope (e.g. event context) can refer to a tag field located in upper levels (e.g. in the event header) by specifying, in this case, the associated tag with . This allows, for instance, the event context to define a variant referring to the "id" field of the event header as selector. The target dynamic scope must be specified explicitly when referring to a field outside of the local static scope. The dynamic scope prefixes are thus: - Stream Packet Context: , - Event Header: , - Stream Event Context: , - Event Context: , - Event Payload: . Multiple declarations of the same field name within a single scope is not valid. It is however valid to re-use the same field name in different scopes. There is no possible conflict, because the dynamic scope must be specified when a variant refers to a tag field located in a different dynamic scope. 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 Appendix C. TSDL Grammar. This section presents a rather ligher reading that consists in examples of TSDL metadata, with template values. Note that the trace endianness is usually extracted from the packet header magic number. The "endian" field is only needed when the magic number packet header field is not present. trace { major = value; /* Trace format version */ minor = value; uuid = "aaaaaaaa-aaaa-aaaa-aaaa-aaaaaaaaaaaa"; /* Trace UUID */ endian = big OR little; /* Endianness (optional) */ packet.header := struct { uint32_t magic; uint8_t trace_uuid[16]; uint32_t stream_id; }; }; 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 = stream_id; context := struct { ... }; fields := struct { ... }; }; /* More detail on types in section 4. Types */ /* * 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. */ struct { ... } variant { ... } enum : integer_type { ... } typedef type new_type[length]; struct { type field_name[length]; } typedef type new_type[length_type]; struct { type field_name[length_type]; } integer { ... } floating_point { ... } struct { integer_type field_name:size; /* GNU/C bitfield */ } struct { string field_name; } 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. #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. The event stream header will therefore be referred to as the "event packet header" throughout the rest of this document. C. TSDL Grammar /* * 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. */ 1) Lexical grammar 1.1) Lexical elements token: keyword identifier constant string-literal punctuator 1.2) Keywords keyword: is one of const char double enum event floating_point float integer int long short signed stream string struct trace typealias typedef unsigned variant void _Bool _Complex _Imaginary 1.3) Identifiers 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 */ 1.4) Universal character names universal-character-name: \u hex-quad \U hex-quad hex-quad hex-quad: hexadecimal-digit hexadecimal-digit hexadecimal-digit hexadecimal-digit 1.5) Constants 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 digit-sequence: digit digit-sequence digit hexadecimal-digit-sequence: hexadecimal-digit hexadecimal-digit-sequence hexadecimal-digit 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 1.6) String literals 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 1.7) Punctuators punctuator: one of [ ] ( ) { } . -> * + - < > : ; ... = , 2) Phrase structure grammar 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: unary-expression constant-expression-range: constant-expression ... constant-expression 2.2) Declarations: 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 struct-specifier: struct identifier-opt { struct-or-variant-declaration-list-opt } struct identifier 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 storage-class-specifier declaration-specifiers declarator-list ; typealias declaration-specifiers abstract-declarator-list := declaration-specifiers abstract-declarator-list ; typealias declaration-specifiers abstract-declarator-list := 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 : constant-expression variant-specifier: variant identifier-opt variant-tag-opt { struct-or-variant-declaration-list } variant identifier variant-tag variant-tag: < identifier > 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 = constant-expression enumeration-constant = constant-expression-range type-qualifier: const declarator: pointer-opt direct-declarator direct-declarator: identifier ( declarator ) direct-declarator [ type-specifier ] direct-declarator [ constant-expression ] abstract-declarator: pointer-opt direct-abstract-declarator direct-abstract-declarator: identifier-opt ( abstract-declarator ) direct-abstract-declarator [ type-specifier ] direct-abstract-declarator [ constant-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 2.3) CTF-specific declarations ctf-specifier: event { ctf-assignment-expression-list-opt } stream { ctf-assignment-expression-list-opt } trace { ctf-assignment-expression-list-opt } typealias declaration-specifiers abstract-declarator-list := declaration-specifiers abstract-declarator-list ; typealias declaration-specifiers abstract-declarator-list := declarator-list ; ctf-type-specifier: floating_point { ctf-assignment-expression-list-opt } integer { ctf-assignment-expression-list-opt } string { ctf-assignment-expression-list-opt } 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 storage-class-specifier declaration-specifiers declarator-list typealias declaration-specifiers abstract-declarator-list := declaration-specifiers abstract-declarator-list typealias declaration-specifiers abstract-declarator-list := declarator-list