Provided by: dpkg-dev_1.14.20ubuntu6_all bug

NAME

       dpkg-gensymbols  -  generate  symbols  files (shared library dependency
       information)

SYNOPSIS

       dpkg-gensymbols [options]

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
       provided  by  the maintainer. It looks for the following files (and use
       the first that is found):

       ·   debian/package.symbols.arch

       ·   debian/symbols.arch

       ·   debian/package.symbols

       ·   debian/symbols

       The main interest of those files is  to  provide  the  minimal  version
       associated  to  each  symbol  provided  by  the  libraries.  Usually it
       corresponds 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.
       Furthermore if the difference are 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
       associated  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
       version  number  but  the  same  upstream  version  still  satisfy  the
       generated  dependencies.   If  the  Debian  revision  can’t  be dropped
       because the symbol 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
       disappear, so the patch should ideally only add new lines.

   Using includes
       When  the set of exported symbols differ between architectures, it’s no
       more possible to  use  a  common  symbols  file.  Using  one  file  per
       architecture works, but it can also lead to duplication of information.
       In those cases, 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 "packages.symbols.common"

       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.

       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

   Using wildcards with versioned symbols
       Well  maintained  libraries  have  versioned symbols where each version
       corresponds to the upstream version where  the  symbol  got  added.  If
       that’s  the  case,  it’s possible to write a symbols file with wildcard
       entries like "*@GLIBC_2.0" that would match any  symbol  associated  to
       the  version GLIBC_2.0. It’s still possible to include specific symbols
       in the file, they’ll take precedence over any matching wildcard  entry.
       An example:

       libc.so.6 libc6 #MINVER#
        *@GLIBC_2.0 2.0
        [...]
        *@GLIBC_2.7 2.7
        access@GLIBC_2.0 2.2

       The  symbol access@GLIBC_2.0 will lead to a minimal dependency on libc6
       version 2.2 despite the wildcard  entry  *@GLIBC_2.0  which  associates
       symbols versioned as GLIBC_2.0 with the minimal version 2.0.

       Note  that  using  wildcards means that dpkg-gensymbols can’t check for
       symbols that might have disappeared and can’t generate a  diff  between
       the  maintainer-supplied  symbols  file  and  the  generated one in the
       binary package.

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

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

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

       ·   it doesn’t export private symbols.

       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
              package  is  listed  in  debian/control  (or   if   there’s   no
              debian/control file).

       -vversion
              Define  the  package  version. Defaults to the version extracted
              from debian/changelog. Required if called outside  of  a  source
              package tree.

       -elibrary-file
              Only  analyze libraries explicitly listed instead of finding all
              public libraries. You can use a regular expression  in  library-
              file   to  match  multiple  libraries  with  a  single  argument
              (otherwise you need multiple -e).

       -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.

       -c[0-4]
              Define  the  checks  to  do when comparing the generated symbols
              file with the 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 disables all checks. 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
              disappeared.   Level   4  fails  if  some  libraries  have  been
              introduced.

              This  value  can  be  overridden  by  the  environment  variable
              DPKG_GENSYMBOLS_CHECK_LEVEL.

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

       -h, --help
              Show the usage message and exit.

       --version
              Show the version and exit.

SEE ALSO

       http://people.redhat.com/drepper/symbol-versioning
       http://people.redhat.com/drepper/goodpractice.pdf
       http://people.redhat.com/drepper/dsohowto.pdf
       deb-symbols(5), dpkg-shlibdeps(1).

AUTHORS

       Copyright (C) 2007 Raphaël Hertzog

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