Update alignment section

[ctf.git] / common-trace-format-proposal.txt

diff --git a/common-trace-format-proposal.txt b/common-trace-format-proposal.txt
index 361c2ec39c21f35ceb06363b218b0c683113d284..ab77a268fd1542145ba6d260b606d58880448afb 100644 (file)
--- a/common-trace-format-proposal.txt
+++ b/common-trace-format-proposal.txt
@@ -68,14 +68,10 @@ A metadata event stream contains information on trace event types. It describes:
 3. Event stream
 
 An event stream is divided in contiguous event packets of variable size. These
 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 rationale for the event stream design choices is
-explained in Appendix B. Stream Header Rationale.
-
-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.
+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.
 
 The event stream header will therefore be referred to as the "event packet
 header" throughout the rest of this document.


@@ -103,15 +99,16 @@ types, but must be derived into a type to be usable in an event field.
 
 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
 
 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

-"bitfields" section.
+"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
 
 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 nor its parents, it is assumed to be bit-packed
-for bitfields and byte-packed for other types.
+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:
 
 
 Metadata attribute representation of a specific alignment:
 


@@ -765,20 +762,23 @@ contained within the payload. (This follows the ISO/C standard for structures)
 
 7. Metadata
 
 
 7. Metadata
 

-The meta-data is located in a stream named "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 null-terminated "string" payload, which is a metadata description
-entry. 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
-and trace UUID. The trace UUID is represented as a string of hexadecimal digits
-and dashes "-".
-
-The metadata can be parsed by reading through the metadata strings, skipping
-newlines and null-characters. Type names are made of a single identifier, and
-can be surrounded by prefix/postfix. 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.
+The meta-data is 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 null-terminated "string"
+payload, which is a metadata description entry. 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 and trace
+UUID. 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 through the metadata strings,
+skipping null-characters. Type names are made of a single identifier,
+and can be surrounded by prefix/postfix. 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.

 
 
 7.1 Declaration vs Definition
 
 
 7.1 Declaration vs Definition


@@ -791,10 +791,12 @@ 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,
 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.
+similarly to C99. The enumeration type specifier and variant tag name
+(both specified with "<" ">") are part of the type specifier.

 
 A definition associates a type to a location in the event structure
 
 A definition associates a type to a location in the event structure

-hierarchy (see Section 6).
+hierarchy (see Section 6). This association is denoted by ":=", as shown
+in Section 7.3.

 
 
 7.2 Metadata Scopes
 
 
 7.2 Metadata Scopes


@@ -845,8 +847,14 @@ 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.
 
 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.

 
 

-7.2 Metadata Examples
+
+7.3 Metadata Examples

 
 The grammar representing the CTF metadata is presented in
 Appendix C. CTF Metadata Grammar. This section presents a rather ligher
 
 The grammar representing the CTF metadata is presented in
 Appendix C. CTF Metadata Grammar. This section presents a rather ligher


@@ -1240,6 +1248,9 @@ unary-operator: one of
 assignment-operator:
        =
 
 assignment-operator:
        =
 

+type-assignment-operator:
+       :=
+

 constant-expression:
        unary-expression
 
 constant-expression:
        unary-expression
 


@@ -1249,11 +1260,11 @@ constant-expression-range:
 2.2) Declarations:
 
 declaration:
 2.2) Declarations:
 
 declaration:

-       declaration-specifiers ;
-       declaration-specifiers storage-class-specifier declaration-specifiers declarator-list ;
+       declaration-specifiers declarator-list-opt ;

        ctf-specifier ;
 
 declaration-specifiers:
        ctf-specifier ;
 
 declaration-specifiers:

+       storage-class-specifier declaration-specifiers-opt

        type-specifier declaration-specifiers-opt
        type-qualifier declaration-specifiers-opt
 
        type-specifier declaration-specifiers-opt
        type-qualifier declaration-specifiers-opt
 


@@ -1280,6 +1291,7 @@ type-specifier:
        unsigned
        _Bool
        _Complex
        unsigned
        _Bool
        _Complex

+       _Imaginary

        struct-specifier
        variant-specifier
        enum-specifier
        struct-specifier
        variant-specifier
        enum-specifier