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

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

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

DESCRIPTION
       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
       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 disappeared.

   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
       optional
           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 behaviour 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 optional.

       arch=architecture-list
       arch-bits=architecture-bits
       arch-endian=architecture-endianness
           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

       allow-internal
           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”.

       ignore-blacklist
           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.

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

       regex
           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 information.

       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 types:

       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:

            libdummy.so.1 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.

       symver
           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 example:

            libc.so.6 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
           behaviour is needed.

       regex
           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:

            libdummy.so.1 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 pattern.

       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 ways:

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

1.21.22                           2023-05-11                deb-src-symbols(5)

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