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    Command:

    dpkg-gensymbols

    
    
    
    

    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):
    
           ?   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 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-
    
       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
                  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
                  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,
           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
    
              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:
               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:
    
           ?   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;
    
           ?   ideally, it uses symbol versioning to achieve ABI stability despite
               internal changes and API extension;
    
           ?   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-
    
           -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.
    
    
           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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