Go to most recent revision | Blame | Compare with Previous | Last modification | View Log | RSS feed
<?xml version="1.0" standalone="no"?>
<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.4//EN"
"http://www.oasis-open.org/docbook/xml/4.4/docbookx.dtd">
<!--
$Id$
-->
<book>
<bookinfo>
<title>The TDF Linker</title>
<corpauthor>The TenDRA Project</corpauthor>
<author>
<firstname>Jeroen</firstname>
<surname>Ruigrok van der Werven</surname>
</author>
<authorinitials>JRvdW</authorinitials>
<pubdate>2006</pubdate>
<copyright>
<year>2006</year>
<holder>The TenDRA Project</holder>
</copyright>
<copyright>
<year>1998</year>
<holder>DERA</holder>
</copyright>
</bookinfo>
<chapter id="introduction">
<title>Introduction</title>
<para>This document describes the formats of the files used by the TDF
linker and the linker's required behaviour. There are two file formats:
the capsule format and the library format. It also describes the format
of the linker information units within capsules. The capsule format is
described in more detail in the TDF specification.</para>
</chapter>
<chapter id="basic-tdf-structures">
<title>Basic TDF structures</title>
<para>The structure of a TDF capsule is defined properly in the TDF
specification. This section describes the basic components of the TDF
format that the linker uses, and the remaining sections describe the
format of a TDF capsule, a TDF library and a linker information unit in
terms of these components. The basic components are:
<table id="tdf-components-and-their-meanings">
<title>TDF components and their meanings</title>
<tgroup cols="2">
<tbody>
<row>
<entry><code>ALIGN</code></entry>
<entry>This is a byte alignment. It forces the next object to
begin on an eight bit boundary.</entry>
</row>
<row>
<entry><code>TDFINT</code></entry>
<entry>This is an unsigned number of unbounded size. Its
representation is described properly in the TDF specification.
It is a series of nibbles (four bits), with the high bit used
as a terminator and the low three bits used as an octal digit.
The terminator bit is set on the final octal digit. As an
example, the number ten would be represented (in binary) as:
0001 1010.</entry>
</row>
<row>
<entry><code>BYTE</code></entry>
<entry>This is an eight bit quantity. <code>BYTE</code>s are
always aligned on an eight bit boundary.</entry>
</row>
<row>
<entry><code>TDFIDENT</code></entry>
<entry>A <code>TDFIDENT</code> is a sequence of characters. It
is possible to change the size of the characters, although the
current implementation will produce an error for
<code>TDFIDENT</code> s with character sizes other than eight
bits. A <code>TDFIDENT</code> is represented by two
<code>TDFINT</code>s (the size of the characters in bits and
the number of characters in the <code>TDFIDENT</code>), and a
sequence of <code>BYTE</code>s.</entry>
</row>
<row>
<entry><code>UNIQUE</code></entry>
<entry>A <code>UNIQUE</code> is a list of <code>TDFIDENT</code>
s. It is represented as a <code>TDFINT</code> specifying the
number of <code>TDFIDENT</code>s in the <code>UNIQUE</code>,
followed by that many <code>TDFIDENT</code>s.</entry>
</row>
<row>
<entry><code>EXTERNAL</code></entry>
<entry>An <code>EXTERNAL</code> is a mechanism for identifying
external identifiers. It is represented as a discriminating
tag, followed by a byte alignment, followed by either a
<code>TDFIDENT</code> or a <code>UNIQUE</code>. The tag is a
two bit number, where one represents a <code>TDFIDENT</code>,
two represents a <code>UNIQUE</code>, and zero and three are
currently illegal. <code>UNIQUE</code> s are only used as part
of an <code>EXTERNAL</code>; <code>TDFIDENT</code> s are used
as entities in their own right, as well as in
<code>EXTERNAL</code> s.</entry>
</row>
</tbody>
</tgroup>
</table>
</para>
<para>In the following descriptions, the syntax <token>name: type</token>
is used to specify an object in the structure. The <token>name</token>
is used to describe the purpose of the object; the <token>type</token>
is used to describe what the object is. A <token>type</token> is one of
the following:
<table id="token-types">
<title>Token types</title>
<tgroup cols="2">
<thead>
<row>
<entry>Type</entry>
<entry>Meaning</entry>
</row>
</thead>
<tbody>
<row>
<entry><token>basic_type</token></entry>
<entry>This represents one of the basic types listed
above.</entry>
</row>
<row>
<entry><token>type</token> * <token>integer</token></entry>
<entry>This represents a sequence of objects of the specified
type. The <token>integer</token> may be either an integer
literal, or a name that has been previously mentioned and is a
<code>TDFINT</code> object.</entry>
</row>
<row>
<entry>{ <token>name1</token>: <token>type1</token> ...
<token>nameN</token>: <token>typeN</token> }</entry>
<entry>This represents a structure composed of the elements
<token>name1: type1</token> to <token>nameN: typeN</token>.
It is used for sequences of objects where the objects are
not of basic types.</entry>
</row>
<row>
<entry><token>type</token> = ( <token>value1</token> | ... |
<token>valueN</token> )</entry>
<entry>This represents a type with a constraint imposed upon it.
The object value must be one of <token>value1</token> to
<token>valueN</token>.</entry>
</row>
</tbody>
</tgroup>
</table>
</para>
</chapter>
<chapter id="structure-of-a-tdf-capsule">
<title>Structure of a TDF Capsule</title>
<para>A TDF capsule has the following structure:
<programlisting>
magic BYTE * 4 = "TDFC"
major_version TDFINT
minor_version TDFINT
ALIGN
num_prop_names: TDFINT
prop_names: TDFIDENT * num_prop_names
num_linkable_entities: TDFINT
linkable_entities: {
name: TDFIDENT
num_capsule_scope_identifiers: TDFINT
} * num_linkable_entities
num_external_linkages: TDFINT = num_linkable_entities
external_linkages: {
num_entries: TDFINT
entries: {
capsule_scope_id: TDFINT
external_name: EXTERNAL
} * num_entries
} * num_external_linkages
num_unit_groups: TDFINT = num_prop_names
unit_groups: {
num_units: TDFINT
units: {
num_counts: TDFINT = (num_linkable_entities | 0)
counts: TDFINT * num_counts
num_link_sets: TDFINT = num_counts
link_sets: {
num_links: TDFINT
links: {
internal: TDFINT
external: TDFINT
} * num_links
} * num_link_sets
num_bytes_tdf: TDFINT
tdf: BYTE * num_bytes_tdf
} * num_units
} * num_unit_groups
</programlisting></para>
<para>The rest of this section describes the format of a capsule.</para>
<para>The capsule begins with a header that contains a four byte magic
number (<token>magic</token>: "TDFC"), followed by the major
(<token>major_version</token>) and minor (<token>minor_version</token>)
version numbers of the TDF in the capsule. This is then followed by a
byte alignment and then the the capsule body.</para>
<para>The first part of a capsule tells the linker how many types of unit
groups there are in the capsule (<token>num_prop_names</token>), and
what the names of these unit group types are
(<token>prop_names</token>). There can be many unit group types, but
the linker must know what they are called, and the order in which they
should occur. At present the linker knows about <token>tld</token>,
<token>tld2</token>, <token>versions</token>, <token>tokdec</token>,
<token>tokdef</token>, <token>aldef</token>, <token>diagtype</token>,
<token>tagdec</token>, <token>diagdef</token>, <token>tagdef</token> and
<token>linkinfo</token> (this can be changed from the command line).
There is nothing special about any unit group type except for the
<token>tld</token> unit group type, which contains information that the
linker uses (and the <token>tld2</token> unit group type, which is
obsolete, but is treated as a special case of the <token>tld</token>
unit group type). The format of the <token>tld</token> unit group type
is described in a later section.</para>
<para>The second part of the capsule tells the linker how many linkable
entities it should be linking on (<token>num_linkable_entities</token>),
the name of each linkable entity (<token>name</token>), and the number
of identifiers of each linkable entity at capsule scope
(<token>num_capsule_scope_identifiers</token>). Identifiers at capsule
scope should be numbers from zero to one less than
<token>num_capsule_scope_identifiers</token>. The identifier allocation
may be sparse, but the linker is optimized for continuous identifier
allocation.</para>
<para>The third part of the capsule tells the linker which external names
the capsule contains for each linkable entity. For each linkable entity
listed in the second part, the number of external names of that linkable
entity are listed in this part (<token>num_entries</token>), along with
each of the external names (<token>external_name</token>) and the
corresponding capsule scope identifiers
(<token>capsule_scope_id</token>). The ordering of the linkable entities
in part three must be identical to the ordering of linkable entities in
part two.</para>
<para>The fourth and final part of the capsule contains the unit groups
themselves. The unit groups occur in the same order as the unit group
types were listed in part one. For each unit group, there is a
<code>TDFINT</code> specifying the number of units in that unit group
(<token>num_units</token>), followed by that many units.</para>
<para>Each unit contains a list of counts (<token>counts</token>) and the
number of counts in that list (<token>num_counts</token>), which must be
either zero or the same as the number of linkable entities in the
capsule (<token>num_linkable_entities</token> ). Each count contains the
number of unit scope identifiers of the given linkable entity in the
unit. If the number of counts is non-zero, then the counts must be in
the same order as the linkable entity names.</para>
<para>After the counts come the unit scope identifier to capsule scope
identifier mapping tables. The number of these tables is specified by
<token>num_link_sets</token> and must be the same as the number of
counts (<token>num_counts</token>), which is either zero or the same as
the number of linkable entities in the capsule. There is one table for
each linkable entity (if <token>num_link_sets</token> is non-zero), and
each table contains <token>num_links</token> pairs of
<code>TDFINT</code>s. The <token>internal</token> <code>TDFINT</code> is
the unit scope identifier; the <token>external</token>
<code>TDFINT</code> is the capsule scope identifier.</para>
<para>After the mapping tables there is a length
(<token>num_bytes_tdf</token>), and that many bytes of TDF data
(<token>tdf</token>).</para>
</chapter>
<chapter id="linker-information-unit">
<title>Linker information unit groups</title>
<para>The <token>tld</token> unit group (if it exists in the capsule)
should contain one unit only. This unit should begin with two zeroes
(i.e. no counts, and no identifier mapping tables), a length (which must
be correct), and a sequence of bytes.</para>
<para>The bytes encode information useful to the linker. The first thing
in the byte sequence of a <token>tld</token> unit is a
<code>TDFINT</code> that is the type of the unit. What follows depends
upon the type. There are currently two types that are supported: zero
and one. Type zero units contain the same information as the old
<token>tld2</token> units (if a <token>tld2</token> unit is read, it is
treated as if it were a <token>tld</token> unit that began with a type
of zero; it is illegal for a capsule to contain both a
<token>tld</token> unit group and a <token>tld2</token> unit group).
Type one units contain more information (described below), and are what
the linker writes out in the generated capsule.</para>
<para>A version one unit contains a sequence of <code>TDFINT</code>s.
There is one <code>TDFINT</code> for each external name in part two of
the capsule. These <code>TDFINT</code>s should be in the same order as
the external names were. The <code>TDFINT</code>s are treated as a
sequence of bits, with the following meanings:
<table id="tdfint-bit-meanings">
<title>TDFINT bit meanings</title>
<tgroup cols="2">
<thead>
<row>
<entry>Bit</entry>
<entry>Meaning</entry>
</row>
</thead>
<tbody>
<row>
<entry>0</entry>
<entry>The name is used within this capsule.</entry>
</row>
<row>
<entry>1</entry>
<entry>The name is declared within this capsule.</entry>
</row>
<row>
<entry>2</entry>
<entry>The name is uniquely defined within this capsule. If this
bit is set for a tag, then the declared bit must also be set
(i.e. a declaration must exist).</entry>
</row>
<row>
<entry>3</entry>
<entry>The name is defined in this capsule, but may have other
definitions provided by other capsules. This bit may not be
set for tokens. If a tag has this bit set, then the declared
bit must also be set (i.e. a declaration must exist).</entry>
</row>
</tbody>
</tgroup>
</table>
</para>
<para>All of the other bits in the <code>TDFINT</code> are reserved. The
linker uses the information provided by this unit to check that names do
not have multiple unique definitions, and to decide whether libraries
should be consulted to provide a definition for an external name. If a
capsule contains no linker information unit group, then the external
names in that capsule will have no information, and hence these checks
will not be made. A similar situation arises when the information for a
name has no bits set.</para>
<para>A version zero unit contains a sequence of <code>TDFINT</code>s.
There is one <code>TDFINT</code> for each external token name, and one
<code>TDFINT</code> for each external tag name. These
<code>TDFINT</code>s should be in the same order as the external names
were (but the tokens always come before the tags). The
<code>TDFINT</code>s are treated as a sequence of bits, with the same
meanings as above.</para>
</chapter>
<chapter id="structure-of-a-tdf-library">
<title>Structure of a TDF library</title>
<para>A TDF library begins with a header, followed by a
<code>TDFINT</code>, that is the type of the library. At present only
type zero libraries are supported. The format of a type zero library is
as follows:
<programlisting>
magic: BYTE * 4 = "TDFL"
major_version: TDFINT
minor_version: TDFINT
ALIGN
type: TDFINT = 0
num_capsules: TDFINT
capsules: {
capsule_name: TDFIDENT
capsule_length: TDFINT
capsule_body: BYTE * capsule_length
} * num_capsules
num_linkable_entities: TDFINT
linkable_entities: {
linkable_entity_name: TDFIDENT
num_this_linkable_entity: TDFINT
this_linkable_entity_names: {
name: EXTERNAL
info: TDFINT
capsule: TDFINT
} * num_this_linkable_entity
} * num_linkable_entities
</programlisting></para>
<para>The library begins with a four byte magic number
(<token>magic</token>: "TDFL"), followed by the major
(<token>major_version</token>) and minor (<token>minor_version</token>)
versions of the TDF in the library (the major version must be the same
for each capsule in the library; the minor version is the highest of the
minor version numbers of all of the the capsules contained in the
library). This is followed by a byte alignment, the type of the library
(<token>type</token>: 0), and the number of capsules in the library
(<token>num_capsules</token>), followed by that many capsules.</para>
<para>Each of the <token>capsules</token> has a name
(<token>capsule_name</token>), and the capsule content, which consists
of the length of the capsule (<token>capsule_length</token> ) and that
many bytes (<token>capsule_body</token>). The capsule name is the name
of the file from which the capsule was obtained when the library was
built. The names of capsules within a library must all be
different.</para>
<para>The library is terminated by the index. This contains information
about where to find definitions for external names. The index begins
with the number of linkable entities whose external names the library
will provide definitions for
(<token>num_linkable_entities</token>).</para>
<para>For each of these linkable entities, the linkable entity index
begins with the name of the linkable entity
(<token>linkable_entity_name</token>), followed by the number of
external names of the linkable entity that have entries in the index
(<token>num_this_linkable_entity</token>). This is followed by the index
information for each of the names.</para>
<para>For each name, the index contains the name (<token>name</token>); a
<code>TDFINT</code> that provides information about the name
(<token>info</token>) with the same meaning as the <code>TDFINT</code>s
in the linker information units; and the index of the capsule that
contains the definition for the name (<token>capsule</token>). The index
of the first capsule is zero.</para>
</chapter>
<chapter id="purpose">
<title>Purpose</title>
<para>The TDF linker has four uses:
<itemizedlist>
<listitem>
<para>To bind together a number of TDF capsules (including those in
libraries) to produce a single capsule.</para>
</listitem>
<listitem>
<para>To produce a TDF library from a set of capsules.</para>
</listitem>
<listitem>
<para>To list the contents of a TDF library.</para>
</listitem>
<listitem>
<para>To extract capsules from a TDF library.</para>
</listitem>
</itemizedlist></para>
<para>The most complex part of the linker is the normal linking process,
which is described in the next section. Constructing libraries is
described in the section after the one on linking. Listing the contents
of a library, and extracting capsules from a library are not very
complicated so they aren't described in this document.</para>
</chapter>
<chapter id="tdf-linking">
<title>TDF Linking</title>
<para>This section describes the requirements of linking capsules
together. The first sub-section describes the basic linking
requirements. Subsequent sub-sections detail the requirements of
some more advanced features.</para>
<para>Before the linking process is described in detail, here is an
outline of the stages of the link process:
<itemizedlist>
<listitem>
<para>The linker is invoked with the following inputs: a set of
input capsules, a set of libraries, a set of hiding rules, a set
of keeping rules, a set of renaming rules, and a set of link
suppression rules.</para>
</listitem>
<listitem>
<para>The first thing that the linker does is to enter the renaming
rules into the name hash table. The name entry lookup routines
will automatically pick up the new name when a renamed name is
looked up in a name table.</para>
</listitem>
<listitem>
<para>The next stage is to load the input capsules, and to bind them
together. As part of this binding process, the capsule scope
identifiers for all input capsules are mapped into a single
capsule scope (to be output to the final capsule). The rules for
this mapping are described below.</para>
</listitem>
<listitem>
<para>After binding the input capsules together, the linker tries to
provide definitions for undefined names using the specified
libraries. When a definition is found in a library (and it hasn't
been suppressed by the link suppression rules), the capsule that
contains it is loaded and bound to the input capsules as if it had
been one itself.</para>
</listitem>
<listitem>
<para>After the library capsules have been bound in, external names
are hidden according to the hiding rules, and kept according to
the keeping rules. Hiding means removing an entry from the
external name list of the output capsule. Keeping means forcing an
entry into the list, if it would otherwise be hidden. It is
illegal to hide names that have no definition.</para>
</listitem>
<listitem>
<para>Finally the output capsule is written to a file.</para>
</listitem>
</itemizedlist></para>
<sect1 id="basic-linking">
<title>Basic linking</title>
<para>This sub-section describes the process of binding capsules
together in greater detail.</para>
<para>The first thing that the linker does when reading a capsule is to
read in the magic number, and the major and minor version numbers.
Capsules with an incorrect magic number are rejected. The major
version number of each capsule read in must be at least four. In
addition, the major version numbers of all capsules that are read in
must be the same.</para>
<para>After this, the linker reads the unit group type names (also
called `prop names'), and checks that the they are known and that they
are in the correct order. There is a default list of names built into
the linker (the list specified in the TDF specification) and that
should be sufficient for most uses of the linker, but it is possible
to provide a new list by specifying a file containing the new list on
the command line.</para>
<para>The next thing the linker does is to read in the linkable entity
names and the capsule scope identifier limit for each linkable entity.
It checks that there are no duplicate names, and creates a mapping
vector for each linkable entity, to contain the mapping from the
capsule scope identifiers in the capsule being read in to the capsule
scope identifiers in the capsule that will be written out.</para>
<para>After reading the linkable entity names, the linker reads the
external names for each linkable entity. For each name, it checks that
its capsule scope identifier is in range, and maps that to the next
available capsule scope identifier (for the same linkable entity) in
the output capsule, unless a name with the same linkable entity and
the same name (subject to the renaming rules) has already been read
(in which case it is mapped to the same capsule scope identifier as
the identical name). The linker also checks to ensure that each
capsule scope identifier has no more than one external name bound to
it.</para>
<para>The final phase of reading a capsule is to read the unit groups.
For normal (i.e. not <token>tld</token> or <token>tld2</token>) unit
groups, the following occurs for each unit in the unit group:
<itemizedlist>
<listitem>
<para>The unit scope identifier limits for each linkable entity
are read and saved in the unit data structure (which is appended
to the list of units in that unit group for all input capsules).
When the unit is written out in the output capsule, it may be
necessary to add extra unit scope identifier limits (and extra
mapping tables) as other capsules may have different linkable
entities, which will also need entries (they will just be zero
length).</para>
</listitem>
<listitem>
<para>The capsule scope to unit scope identifier mapping tables
are read, and the old capsule scope identifier (which is first
checked to see if it is in range) is replaced by a new capsule
scope identifier. This information is also saved in the unit
data structure. The new capsule scope identifiers are either the
ones that were allocated when reading in the external names (if
the old identifier is bound to an external name), or the next
free capsule scope identifier of the required linkable
entity.</para>
</listitem>
<listitem>
<para>Finally, the unit body is read, and saved with the
unit.</para>
</listitem>
</itemizedlist></para>
<para>For <token>tld</token> and <token>tld2</token> unit groups, the
unit group count is checked to ensure that it is one, and the number
of unit scope identifier limits and identifier mapping tables are
checked to ensure that they are both zero. The size of the body is
read (and it must be correct as this is checked after reading the
unit), and then the body is read. If the unit is a <token>tld</token>
unit, then the type is read, and the body is read depending upon the
type; if the unit is a <token>tld2</token> unit, then the body is read
as if it where a type zero <token>tld</token> unit.</para>
<para>A type zero <token>tld</token> unit consists of a number of
integers: one for each external token name, followed by one for each
external tag name (in the same order as the external name tables, but
tokens always precede tags). A type one <token>tld</token> unit
consists of a number of integers: one for each external name (of all
linkable entities), in the same order as the external name
tables.</para>
<para>Each of the integers is interpreted as a series of bits, with the
bits having the following meanings:
<table id="type-zero-unit-integer-meanings">
<title>Type zero unit integer meanings</title>
<tgroup cols="2">
<thead>
<row>
<entry>Bit</entry>
<entry>Meaning</entry>
</row>
</thead>
<tbody>
<row>
<entry>0</entry>
<entry>The name is used within this capsule.</entry>
</row>
<row>
<entry>1</entry>
<entry>The name is declared within this capsule.</entry>
</row>
<row>
<entry>2</entry>
<entry>The name is uniquely defined within this capsule. If
this bit is set for a tag, then the declared bit must also
be set. It is illegal to have a name uniquely defined in
more than one capsule. If this occurs, the linker will
report an error.</entry>
</row>
<row>
<entry>3</entry>
<entry>The name is defined in this capsule, but may have other
definitions provided by other capsules. This bit may not be
set for tokens. If a tag has this bit set, the declared bit
must also be set. It is possible for a name to provide a
unique definition, but still allow other non-unique
definitions to be linked in from other capsules.</entry>
</row>
</tbody>
</tgroup>
</table>
</para>
<para>All of the other bits in the integer are reserved. The linker
uses the information provided by this unit to check that names do not
have multiple unique definitions, and to decide whether libraries
should be consulted to provide a definition for a name. If a capsule
contains no linker information unit group, then the names in that
capsule will have no information, and hence will not receive the extra
checking or library definition.</para>
</sect1>
<sect1 id="renaming">
<title>Renaming</title>
<para>Renaming just requires that any occurrence of the name being
renamed is treated as though it were an occurrence of the name it is
being renamed to. This includes names read from library
indices.</para>
</sect1>
<sect1 id="library-capsules">
<title>Library capsules</title>
<para>After reading in all of the specified capsules, the linker loads
the libraries. The library indices are read, and checked to ensure
that there is no more than one definition for any external name. If
there is no unique definition, but there is a single multiple
definition, then this is considered to be a definition (although this
can be turned off with a command line option).</para>
<para>Once the libraries have been loaded, each of the external names in
the bound capsules that are used, but not defined are looked up in the
library index. If a definition is found (and it hasn't been
suppressed) then the defining capsule is loaded from the library. This
process is repeated until definitions have been found for all external
names that need them (and that definitions exist for), including those
that are undefined in the capsules read in from the libraries.</para>
</sect1>
<sect1 id="hiding">
<title>Hiding</title>
<para>Hiding and keeping just require that all names which should be
hidden, and are not required to be kept, are not written to the
external name table of the output capsule.</para>
</sect1>
<sect1 id="writing-out-the-capsule">
<title>Writing out the capsule</title>
<para>The magic number is written out, followed by the major and minor
version numbers. The major version number is the same as that in each
of the loaded capsules. The minor version number is the largest of the
minor version numbers in the loaded capsules.</para>
<para>The unit group type names are written out first. Only those unit
groups that are non-empty are actually written out. They are written
out in the order specified by the current unit group name list.</para>
<para>The linkable entity names are written out next, followed by their
capsule scope identifier limit. Again, only those linkable entity
names that are non empty (i.e. have some unit scope or capsule scope
identifiers) are written out.</para>
<para>After the linkable entity names have been written out, the
external names are written out. These are written out in an arbitrary
order within their linkable entities, with the linkable entities being
written out in the same order as in the linkable entity name section
(which is itself arbitrary, but must be repeatable). The names are
written out with their new capsule scope identifiers. External names
that have been hidden must not be written out.</para>
<para>Finally the unit groups are written out in the same order as the
unit group type names in the first section. For normal units, the old
counts (plus some zero counts that may be necessary if there are new
linkable entities that weren't in the unit's original capsule) are
written out in the same order as the linkable entity names in section
two. The counts are followed by the new capsule scope to unit scope
identifier mapping tables, in the same order as the counts. Finally
the old unit content is written out.</para>
<para>For <token>tld</token> unit groups, a single version one
<token>tld</token> unit is written out containing the use information
for each of the external names, in the same order that the external
names were written out in.</para>
</sect1>
</chapter>
<chapter id="constructing-tdf-libraries">
<title>Constructing TDF Libraries</title>
<para>This section describes the requirements of building TDF libraries.
Here is an outline of the stages of the construction process:</para>
<itemizedlist>
<listitem>
<para>The linker is invoked with the following inputs: a set of input
capsules, a set of libraries, and a set of link suppression
rules.</para>
</listitem>
<listitem>
<para>The first thing that the linker does is to load the input capsules
(including all capsules that are included in any of the specified
libraries), and to extract their external name information into a
central index. The index is checked to ensure that there is only one
definition for any given name. The capsules are read in in the same
way as for linking them (this checks them for validity).</para>
</listitem>
<listitem>
<para>The suppression rules are applied, to ensure that no suppressed
external name will end up in the index in the output library.</para>
</listitem>
<listitem>
<para>The library is written out. The library consists of a magic
number, and the major and minor version numbers of the TDF in the
library (calculated in the same way as for capsules), the type zero,
followed by the number of capsules. This is followed by that many
capsule name and capsule content pairs. Finally, the index is appended
to the library.</para>
</listitem>
<listitem>
<para>The index only contains entries for linkable entities that have
external names defined by the library. Only external names for which
there is a definition are written into the index, although this is not
a requirement (when linking, the linker will ignore index entries that
don't provide a definition). Either a unique definition or a single
multiple definition are considered to be definitions (although the
latter can be disabled using a command line option).</para>
</listitem>
</itemizedlist>
</chapter>
</book>