deb-src-symbols(5) — Linux manual page


deb-src-symbols(5)             dpkg suite             deb-src-symbols(5)

NAME         top

       deb-src-symbols - Debian's extended shared library template file

SYNOPSIS         top

       debian/package.symbols.arch, debian/symbols.arch,
       debian/package.symbols, debian/symbols

DESCRIPTION         top

       The symbol file templates are shipped in Debian source packages,
       and its format is a superset of the symbols files shipped in
       binary packages, see deb-symbols(5).

       Comments are supported in template symbol files. Any line with
       ‘#’ as the first character is a comment except if it starts with
       ‘#include’ (see section Using includes).  Lines starting with
       ‘#MISSING:’ are special comments documenting symbols that have

   Using #PACKAGE# substitution
       In some rare cases, the name of the library varies between
       architectures.  To avoid hardcoding the name of the package in
       the symbols file, you can use the marker #PACKAGE#. It will be
       replaced by the real package name during installation of the
       symbols files. Contrary to the #MINVER# marker, #PACKAGE# will
       never appear in a symbols file inside a binary package.

   Using symbol tags
       Symbol tagging is useful for marking symbols that are special in
       some way.  Any symbol can have an arbitrary number of tags
       associated with it. While all tags are parsed and stored, only
       some of them are understood by dpkg-gensymbols and trigger
       special handling of the symbols. See subsection Standard symbol
       tags for reference of these tags.

       Tag specification comes right before the symbol name (no
       whitespace is allowed in between). It always starts with an
       opening bracket (, ends with a closing bracket ) and must contain
       at least one tag. Multiple tags are separated by the | character.
       Each tag can optionally have a value which is separated form the
       tag name by the = character. Tag names and values can be
       arbitrary strings except they cannot contain any of the special )
       | = characters. Symbol names following a tag specification can
       optionally be quoted with either ' or " characters to allow
       whitespaces in them. However, if there are no tags specified for
       the symbol, quotes are treated as part of the symbol name which
       continues up until the first space.

         (tag1=i am marked|tag name with space)"tagged quoted symbol"@Base 1.0
         (optional)tagged_unquoted_symbol@Base 1.0 1
         untagged_symbol@Base 1.0

       The first symbol in the example is named tagged quoted symbol and
       has two tags: tag1 with value i am marked and tag name with space
       that has no value. The second symbol named tagged_unquoted_symbol
       is only tagged with the tag named optional. The last symbol is an
       example of the normal untagged symbol.

       Since symbol tags are an extension of the deb-symbols(5) format,
       they can only be part of the symbols files used in source
       packages (those files should then be seen as templates used to
       build the symbols files that are embedded in binary packages).
       When dpkg-gensymbols is called without the -t option, it will
       output symbols files compatible to the deb-symbols(5) format: it
       fully processes symbols according to the requirements of their
       standard tags and strips all tags from the output. On the
       contrary, in template mode (-t) all symbols and their tags (both
       standard and unknown ones) are kept in the output and are written
       in their original form as they were loaded.

   Standard symbol tags
           A symbol marked as optional can disappear from the library at
           any time and that will never cause dpkg-gensymbols to fail.
           However, disappeared optional symbols will continuously
           appear as MISSING in the diff in each new package revision.
           This behavior serves as a reminder for the maintainer that
           such a symbol needs to be removed from the symbol file or
           readded to the library. When the optional symbol, which was
           previously declared as MISSING, suddenly reappears in the
           next revision, it will be upgraded back to the “existing”
           status with its minimum version unchanged.

           This tag is useful for symbols which are private where their
           disappearance do not cause ABI breakage. For example, most of
           C++ template instantiations fall into this category. Like any
           other tag, this one may also have an arbitrary value: it
           could be used to indicate why the symbol is considered

           These tags allow one to restrict the set of architectures
           where the symbol is supposed to exist. The arch-bits and
           arch-endian tags are supported since dpkg 1.18.0. When the
           symbols list is updated with the symbols discovered in the
           library, all arch-specific symbols which do not concern the
           current host architecture are treated as if they did not
           exist. If an arch-specific symbol matching the current host
           architecture does not exist in the library, normal procedures
           for missing symbols apply and it may cause dpkg-gensymbols to
           fail. On the other hand, if the arch-specific symbol is found
           when it was not supposed to exist (because the current host
           architecture is not listed in the tag or does not match the
           endianness and bits), it is made arch neutral (i.e. the arch,
           arch-bits and arch-endian tags are dropped and the symbol
           will appear in the diff due to this change), but it is not
           considered as new.

           When operating in the default non-template mode, among arch-
           specific symbols only those that match the current host
           architecture are written to the symbols file. On the
           contrary, all arch-specific symbols (including those from
           foreign arches) are always written to the symbol file when
           operating in template mode.

           The format of architecture-list is the same as the one used
           in the Build-Depends field of debian/control (except the
           enclosing square brackets []). For example, the first symbol
           from the list below will be considered only on alpha,
           any-amd64 and ia64 architectures, the second only on linux
           architectures, while the third one anywhere except on armel.

             (arch=alpha any-amd64 ia64)64bit_specific_symbol@Base 1.0
             (arch=linux-any)linux_specific_symbol@Base 1.0
             (arch=!armel)symbol_armel_does_not_have@Base 1.0

           The architecture-bits is either 32 or 64.

             (arch-bits=32)32bit_specific_symbol@Base 1.0
             (arch-bits=64)64bit_specific_symbol@Base 1.0

           The architecture-endianness is either little or big.

             (arch-endian=little)little_endian_specific_symbol@Base 1.0
             (arch-endian=big)big_endian_specific_symbol@Base 1.0

           Multiple restrictions can be chained.

             (arch-bits=32|arch-endian=little)32bit_le_symbol@Base 1.0

           dpkg-gensymbols has a list of internal symbols that should
           not appear in symbols files as they are usually only side-
           effects of implementation details of the toolchain (since
           dpkg 1.20.1).  If for some reason, you really want one of
           those symbols to be included in the symbols file, you should
           tag the symbol with allow-internal.  It can be necessary for
           some low level toolchain libraries like “libgcc”.

           A deprecated alias for allow-internal (since dpkg 1.20.1,
           supported since dpkg 1.15.3).

       c++ Denotes c++ symbol pattern. See Using symbol patterns
           subsection below.

           Denotes symver (symbol version) symbol pattern. See Using
           symbol patterns subsection below.

           Denotes regex symbol pattern. See Using symbol patterns
           subsection below.

   Using symbol patterns
       Unlike a standard symbol specification, a pattern may cover
       multiple real symbols from the library. dpkg-gensymbols will
       attempt to match each pattern against each real symbol that does
       not have a specific symbol counterpart defined in the symbol
       file. Whenever the first matching pattern is found, all its tags
       and properties will be used as a basis specification of the
       symbol. If none of the patterns matches, the symbol will be
       considered as new.

       A pattern is considered lost if it does not match any symbol in
       the library. By default this will trigger a dpkg-gensymbols
       failure under -c1 or higher level. However, if the failure is
       undesired, the pattern may be marked with the optional tag. Then
       if the pattern does not match anything, it will only appear in
       the diff as MISSING. Moreover, like any symbol, the pattern may
       be limited to the specific architectures with the arch tag.
       Please refer to Standard symbol tags subsection above for more

       Patterns are an extension of the deb-symbols(5) format hence they
       are only valid in symbol file templates. Pattern specification
       syntax is not any different from the one of a specific symbol.
       However, symbol name part of the specification serves as an
       expression to be matched against name@version of the real symbol.
       In order to distinguish among different pattern types, a pattern
       will typically be tagged with a special tag.

       At the moment, dpkg-gensymbols supports three basic pattern

       c++ This pattern is denoted by the c++ tag. It matches only C++
           symbols by their demangled symbol name (as emitted by
           c++filt(1) utility). This pattern is very handy for matching
           symbols which mangled names might vary across different
           architectures while their demangled names remain the same.
           One group of such symbols is non-virtual thunks which have
           architecture specific offsets embedded in their mangled
           names. A common instance of this case is a virtual destructor
           which under diamond inheritance needs a non-virtual thunk
           symbol. For example, even if _ZThn8_N3NSB6ClassDD1Ev@Base on
           32bit architectures will probably be
           _ZThn16_N3NSB6ClassDD1Ev@Base on 64bit ones, it can be
           matched with a single c++ pattern:

   libdummy1 #MINVER#
             (c++)"non-virtual thunk to NSB::ClassD::~ClassD()@Base" 1.0

           The demangled name above can be obtained by executing the
           following command:

             $ echo '_ZThn8_N3NSB6ClassDD1Ev@Base' | c++filt

           Please note that while mangled name is unique in the library
           by definition, this is not necessarily true for demangled
           names. A couple of distinct real symbols may have the same
           demangled name. For example, that's the case with non-virtual
           thunk symbols in complex inheritance configurations or with
           most constructors and destructors (since g++ typically
           generates two real symbols for them). However, as these
           collisions happen on the ABI level, they should not degrade
           quality of the symbol file.

           This pattern is denoted by the symver tag. Well maintained
           libraries have versioned symbols where each version
           corresponds to the upstream version where the symbol got
           added. If that's the case, you can use a symver pattern to
           match any symbol associated to the specific version. For

   libc6 #MINVER#
             (symver)GLIBC_2.0 2.0
             (symver)GLIBC_2.7 2.7
             access@GLIBC_2.0 2.2

           All symbols associated with versions GLIBC_2.0 and GLIBC_2.7
           will lead to minimal version of 2.0 and 2.7 respectively with
           the exception of the symbol access@GLIBC_2.0. The latter will
           lead to a minimal dependency on libc6 version 2.2 despite
           being in the scope of the "(symver)GLIBC_2.0" pattern because
           specific symbols take precedence over patterns.

           Please note that while old style wildcard patterns (denoted
           by "*@version" in the symbol name field) are still supported,
           they have been deprecated by new style syntax
           "(symver|optional)version". For example, "*@GLIBC_2.0 2.0"
           should be written as "(symver|optional)GLIBC_2.0 2.0" if the
           same behavior is needed.

           Regular expression patterns are denoted by the regex tag.
           They match by the perl regular expression specified in the
           symbol name field. A regular expression is matched as it is,
           therefore do not forget to start it with the ^ character or
           it may match any part of the real symbol name@version string.
           For example:

   libdummy1 #MINVER#
             (regex)"^mystack_.*@Base$" 1.0
             (regex|optional)"private" 1.0

           Symbols like "mystack_new@Base", "mystack_push@Base",
           "mystack_pop@Base", etc., will be matched by the first
           pattern while "ng_mystack_new@Base" would not.  The second
           pattern will match all symbols having the string "private" in
           their names and matches will inherit optional tag from the

       Basic patterns listed above can be combined where it makes sense.
       In that case, they are processed in the order in which the tags
       are specified. For example, both:

         (c++|regex)"^NSA::ClassA::Private::privmethod\d\(int\)@Base" 1.0
         (regex|c++)N3NSA6ClassA7Private11privmethod\dEi@Base 1.0

       will match symbols "_ZN3NSA6ClassA7Private11privmethod1Ei@Base"
       and "_ZN3NSA6ClassA7Private11privmethod2Ei@Base". When matching
       the first pattern, the raw symbol is first demangled as C++
       symbol, then the demangled name is matched against the regular
       expression. On the other hand, when matching the second pattern,
       regular expression is matched against the raw symbol name, then
       the symbol is tested if it is C++ one by attempting to demangle
       it. A failure of any basic pattern will result in the failure of
       the whole pattern.  Therefore, for example,
       "__N3NSA6ClassA7Private11privmethod\dEi@Base" will not match
       either of the patterns because it is not a valid C++ symbol.

       In general, all patterns are divided into two groups: aliases
       (basic c++ and symver) and generic patterns (regex, all
       combinations of multiple basic patterns). Matching of basic
       alias-based patterns is fast (O(1)) while generic patterns are
       O(N) (N - generic pattern count) for each symbol.  Therefore, it
       is recommended not to overuse generic patterns.

       When multiple patterns match the same real symbol, aliases (first
       c++, then symver) are preferred over generic patterns. Generic
       patterns are matched in the order they are found in the symbol
       file template until the first success.  Please note, however,
       that manual reordering of template file entries is not
       recommended because dpkg-gensymbols generates diffs based on the
       alphanumerical order of their names.

   Using includes
       When the set of exported symbols differ between architectures, it
       may become inefficient to use a single symbol file. In those
       cases, an include directive may prove to be useful in a couple of

       •   You can factorize the common part in some external file and
           include that file in your package.symbols.arch file by using
           an include directive like this:

            #include "I<packages>.symbols.common"

       •   The include directive may also be tagged like any symbol:

            (tag|...|tagN)#include "file-to-include"

           As a result, all symbols included from file-to-include will
           be considered to be tagged with tag ... tagN by default. You
           can use this feature to create a common package.symbols file
           which includes architecture specific symbol files:

             common_symbol1@Base 1.0
            (arch=amd64 ia64 alpha)#include "package.symbols.64bit"
            (arch=!amd64 !ia64 !alpha)#include "package.symbols.32bit"
             common_symbol2@Base 1.0

       The symbols files are read line by line, and include directives
       are processed as soon as they are encountered. This means that
       the content of the included file can override any content that
       appeared before the include directive and that any content after
       the directive can override anything contained in the included
       file. Any symbol (or even another #include directive) in the
       included file can specify additional tags or override values of
       the inherited tags in its tag specification. However, there is no
       way for the symbol to remove any of the inherited tags.

       An included file can repeat the header line containing the SONAME
       of the library. In that case, it overrides any header line
       previously read.  However, in general it's best to avoid
       duplicating header lines. One way to do it is the following:

        #include "libsomething1.symbols.common"
         arch_specific_symbol@Base 1.0

SEE ALSO         top

       deb-symbols(5), dpkg-shlibdeps(1), dpkg-gensymbols(1).

COLOPHON         top

       This page is part of the dpkg (Debian Package Manager) project.
       Information about the project can be found at 
       ⟨⟩.  If you have a bug report
       for this manual page, see
       ⟨⟩.  This
       page was obtained from the project's upstream Git repository ⟨git
       clone⟩ on 2023-06-23.  (At
       that time, the date of the most recent commit that was found in
       the repository was 2023-05-29.)  If you discover any rendering
       problems in this HTML version of the page, or you believe there
       is a better or more up-to-date source for the page, or you have
       corrections or improvements to the information in this COLOPHON
       (which is not part of the original manual page), send a mail to

1.21.20-209-g3026e             2023-02-07             deb-src-symbols(5)

Pages that refer to this page: dpkg-gensymbols(1)deb-symbols(5)