dpkg-gensymbols

       information)

SYNOPSIS
       dpkg-gensymbols [option...]

DESCRIPTION
       dpkg-gensymbols scans a temporary build tree  (debian/tmp  by  default)
       looking for libraries and generate a symbols file describing them. This
       file, if non-empty, is then installed in the DEBIAN subdirectory of the
       build  tree  so  that it ends up included in the control information of
       the package.

       When generating those files, it uses as input some symbols  files  pro-
       vided  by the maintainer. It looks for the following files (and use the
       first that is found):

       o   debian/package.symbols.arch

       o   debian/symbols.arch

       o   debian/package.symbols

       o   debian/symbols

       The main interest of those files is  to  provide  the  minimal  version
       associated  to each symbol provided by the libraries. Usually it corre-
       sponds to the first version of that package that provided  the  symbol,
       but  it can be manually incremented by the maintainer if the ABI of the
       symbol is extended without breaking backwards compatibility.  It's  the
       responsibility  of  the  maintainer  to keep those files up-to-date and
       accurate, but dpkg-gensymbols helps him.

       When the generated symbols files differ from  the  maintainer  supplied
       one,  dpkg-gensymbols will print a diff between the two versions.  Fur-
       thermore if the difference is too significant, it will even  fail  (you
       can customize how much difference you can tolerate, see the -c option).

MAINTAINING SYMBOLS FILES
       The  symbols files are really useful only if they reflect the evolution
       of the package through several releases. Thus  the  maintainer  has  to
       update  them  every time that a new symbol is added so that its associ-
       ated minimal version matches reality. To do this properly  he  can  use
       the  diffs contained in the build logs. In most cases, the diff applies
       directly to his debian/package.symbols file. That said, further  tweaks
       are  usually  needed:  it's  recommended for example to drop the Debian
       revision from the minimal version so that backports with a  lower  ver-
       sion  number  but the same upstream version still satisfy the generated
       dependencies.  If the Debian revision can't be dropped because the sym-
       bol  really  got  added  by the Debian specific change, then one should
       suffix the version with "~".

       Before applying any patch to the symbols file,  the  maintainer  should
       double-check  that it's sane. Public symbols are not supposed to disap-
       pear, so the patch should ideally only add new lines.
       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  a  some  of  them  are
       understood  by dpkg-gensymbols and trigger special handling of the sym-
       bols. 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 spec-
       ification  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 contin-
       ues 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 nor-
       mal 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  out-
       put.  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. How-
              ever,  disappeared  optional symbols will continuously appear as
              MISSING in the diff in each new package revision.   This  behav-
              iour  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.
              ture 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), it is made arch neutral (i.e. the arch tag is 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-spe-
              cific  symbols  only those that match the current host architec-
              ture 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,  amd64,  kfreebsd-amd64
              and  ia64  architectures while the second one anywhere except on
              armel.

               (arch=alpha  amd64  kfreebsd-amd64   ia64)a_64bit_specific_sym-
              bol@Base 1.0
               (arch=!armel)symbol_armel_does_not_have@Base 1.0

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

       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 subsec-
              tion 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.
       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 spe-
       cial 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 destruc-
          tor which under diamond inheritance needs a non-virtual  thunk  sym-
          bol.  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 def-
          inition,  this is not necessarily true for demangled names. A couple
          of distinct real symbols may have the same demangled name. For exam-
          ple,  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  spe-
          cific 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

       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",    "mys-
          tack_pop@Base" etc.  will be matched by the first pattern while e.g.
          "ng_mystack_new@Base" won't.  The second pattern will match all sym-
          bols  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 speci-
       fied. 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 multi-
       ple  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 pat-
       terns.

       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 gener-
       ates 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:

           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.  How-
       ever,  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

   Good library management
       A well-maintained library has the following features:

       o   its  API is stable (public symbols are never dropped, only new pub-
           lic symbols are added) and changes in incompatible ways  only  when
           the SONAME changes;

       o   ideally, it uses symbol versioning to achieve ABI stability despite
           internal changes and API extension;

       o   it doesn't export private  symbols  (such  symbols  can  be  tagged
           optional as workaround).

       While  maintaining the symbols file, it's easy to notice appearance and
       disappearance of symbols. But it's more difficult to catch incompatible
       API  and  ABI  change.  Thus  the maintainer should read thoroughly the
       upstream changelog looking for cases where the rules  of  good  library
       management  have been broken. If potential problems are discovered, the
       upstream author should be notified as an upstream fix is always  better
       than a Debian specific work-around.

OPTIONS
       -Ppackage-build-dir
              Scan package-build-dir instead of debian/tmp.

       -ppackage
              Define  the package name. Required if more than one binary pack-
              age is listed in debian/control (or if there's no debian/control

       -Ifilename
              Use filename as reference file to generate the symbols file that
              is integrated in the package itself.

       -O     Print the generated symbols file to standard output, rather than
              being stored in the package build tree.

       -Ofilename
              Store the generated symbols file as  filename.  If  filename  is
              pre-existing,  its  content  is  used as basis for the generated
              symbols file.  You can use this feature to update a symbols file
              so that it matches a newer upstream version of your library.

       -t     Write  the  symbol  file in template mode rather than the format
              compatible with deb-symbols(5). The main difference is  that  in
              the  template  mode  symbol  names and tags are written in their
              original form contrary to the post-processed symbol  names  with
              tags stripped in the compatibility mode.  Moreover, some symbols
              might be omitted when writing  a  standard  deb-symbols(5)  file
              (according  to  the  tag processing rules) while all symbols are
              always written to the symbol file template.

       -c[0-4]
              Define the checks to do when  comparing  the  generated  symbols
              file  with  the template file used as starting point. By default
              the level is 1. Increasing levels do more checks and include all
              checks  of  lower  levels. Level 0 never fails. Level 1 fails if
              some symbols have disappeared. Level 2 fails if some new symbols
              have  been introduced. Level 3 fails if some libraries have dis-
              appeared. Level 4 fails if some libraries have been introduced.

              This  value  can  be  overridden  by  the  environment  variable
              DPKG_GENSYMBOLS_CHECK_LEVEL.

       -q     Keep  quiet  and never generate a diff between generated symbols
              file and the template file used as starting point  or  show  any
              warnings  about  new/lost  libraries  or  new/lost symbols. This
              option only disables informational output  but  not  the  checks
              themselves (see -c option).

       -aarch Assume  arch  as host architecture when processing symbol files.
              Use this option to generate a symbol file or diff for any archi-
              tecture provided its binaries are already available.

       -d     Enable  debug  mode.  Numerous messages are displayed to explain
              what dpkg-gensymbols does.

       -V     Enable verbose mode. The generated symbols file contains  depre-
              cated symbols as comments. Furthermore in template mode, pattern
              symbols are followed by comments listing real symbols that  have
              matched the pattern.

       -h, --help
       Copyright (C) 2007-2009 Raphael Hertzog

       This  is free software; see the GNU General Public Licence version 2 or
       later for copying conditions. There is NO WARRANTY.



Debian Project                    2011-08-14                dpkg-gensymbols(1)
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