1deb-src-symbols(5)                dpkg suite                deb-src-symbols(5)
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NAME

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

9       debian/package.symbols.arch, debian/symbols.arch,
10       debian/package.symbols, debian/symbols
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DESCRIPTION

13       The symbol file templates are shipped in Debian source packages, and
14       its format is a superset of the symbols files shipped in binary
15       packages, see deb-symbols(5).
16
17   Comments
18       Comments are supported in template symbol files. Any line with ‘#’ as
19       the first character is a comment except if it starts with ‘#include’
20       (see section Using includes).  Lines starting with ‘#MISSING:’ are
21       special comments documenting symbols that have disappeared.
22
23   Using #PACKAGE# substitution
24       In some rare cases, the name of the library varies between
25       architectures.  To avoid hardcoding the name of the package in the
26       symbols file, you can use the marker #PACKAGE#. It will be replaced by
27       the real package name during installation of the symbols files.
28       Contrary to the #MINVER# marker, #PACKAGE# will never appear in a
29       symbols file inside a binary package.
30
31   Using symbol tags
32       Symbol tagging is useful for marking symbols that are special in some
33       way.  Any symbol can have an arbitrary number of tags associated with
34       it. While all tags are parsed and stored, only some of them are
35       understood by dpkg-gensymbols and trigger special handling of the
36       symbols. See subsection Standard symbol tags for reference of these
37       tags.
38
39       Tag specification comes right before the symbol name (no whitespace is
40       allowed in between). It always starts with an opening bracket (, ends
41       with a closing bracket ) and must contain at least one tag. Multiple
42       tags are separated by the | character. Each tag can optionally have a
43       value which is separated form the tag name by the = character. Tag
44       names and values can be arbitrary strings except they cannot contain
45       any of the special ) | = characters. Symbol names following a tag
46       specification can optionally be quoted with either ' or " characters to
47       allow whitespaces in them. However, if there are no tags specified for
48       the symbol, quotes are treated as part of the symbol name which
49       continues up until the first space.
50
51         (tag1=i am marked|tag name with space)"tagged quoted symbol"@Base 1.0
52         (optional)tagged_unquoted_symbol@Base 1.0 1
53         untagged_symbol@Base 1.0
54
55       The first symbol in the example is named tagged quoted symbol and has
56       two tags: tag1 with value i am marked and tag name with space that has
57       no value. The second symbol named tagged_unquoted_symbol is only tagged
58       with the tag named optional. The last symbol is an example of the
59       normal untagged symbol.
60
61       Since symbol tags are an extension of the deb-symbols(5) format, they
62       can only be part of the symbols files used in source packages (those
63       files should then be seen as templates used to build the symbols files
64       that are embedded in binary packages). When dpkg-gensymbols is called
65       without the -t option, it will output symbols files compatible to the
66       deb-symbols(5) format: it fully processes symbols according to the
67       requirements of their standard tags and strips all tags from the
68       output. On the contrary, in template mode (-t) all symbols and their
69       tags (both standard and unknown ones) are kept in the output and are
70       written in their original form as they were loaded.
71
72   Standard symbol tags
73       optional
74           A symbol marked as optional can disappear from the library at any
75           time and that will never cause dpkg-gensymbols to fail. However,
76           disappeared optional symbols will continuously appear as MISSING in
77           the diff in each new package revision.  This behaviour serves as a
78           reminder for the maintainer that such a symbol needs to be removed
79           from the symbol file or readded to the library. When the optional
80           symbol, which was previously declared as MISSING, suddenly
81           reappears in the next revision, it will be upgraded back to the
82           “existing” status with its minimum version unchanged.
83
84           This tag is useful for symbols which are private where their
85           disappearance do not cause ABI breakage. For example, most of C++
86           template instantiations fall into this category. Like any other
87           tag, this one may also have an arbitrary value: it could be used to
88           indicate why the symbol is considered optional.
89
90       arch=architecture-list
91       arch-bits=architecture-bits
92       arch-endian=architecture-endianness
93           These tags allow one to restrict the set of architectures where the
94           symbol is supposed to exist. The arch-bits and arch-endian tags are
95           supported since dpkg 1.18.0. When the symbols list is updated with
96           the symbols discovered in the library, all arch-specific symbols
97           which do not concern the current host architecture are treated as
98           if they did not exist. If an arch-specific symbol matching the
99           current host architecture does not exist in the library, normal
100           procedures for missing symbols apply and it may cause dpkg-
101           gensymbols to fail. On the other hand, if the arch-specific symbol
102           is found when it was not supposed to exist (because the current
103           host architecture is not listed in the tag or does not match the
104           endianness and bits), it is made arch neutral (i.e. the arch, arch-
105           bits and arch-endian tags are dropped and the symbol will appear in
106           the diff due to this change), but it is not considered as new.
107
108           When operating in the default non-template mode, among arch-
109           specific symbols only those that match the current host
110           architecture are written to the symbols file. On the contrary, all
111           arch-specific symbols (including those from foreign arches) are
112           always written to the symbol file when operating in template mode.
113
114           The format of architecture-list is the same as the one used in the
115           Build-Depends field of debian/control (except the enclosing square
116           brackets []). For example, the first symbol from the list below
117           will be considered only on alpha, any-amd64 and ia64 architectures,
118           the second only on linux architectures, while the third one
119           anywhere except on armel.
120
121             (arch=alpha any-amd64 ia64)64bit_specific_symbol@Base 1.0
122             (arch=linux-any)linux_specific_symbol@Base 1.0
123             (arch=!armel)symbol_armel_does_not_have@Base 1.0
124
125           The architecture-bits is either 32 or 64.
126
127             (arch-bits=32)32bit_specific_symbol@Base 1.0
128             (arch-bits=64)64bit_specific_symbol@Base 1.0
129
130           The architecture-endianness is either little or big.
131
132             (arch-endian=little)little_endian_specific_symbol@Base 1.0
133             (arch-endian=big)big_endian_specific_symbol@Base 1.0
134
135           Multiple restrictions can be chained.
136
137             (arch-bits=32|arch-endian=little)32bit_le_symbol@Base 1.0
138
139       allow-internal
140           dpkg-gensymbols has a list of internal symbols that should not
141           appear in symbols files as they are usually only side-effects of
142           implementation details of the toolchain (since dpkg 1.20.1).  If
143           for some reason, you really want one of those symbols to be
144           included in the symbols file, you should tag the symbol with allow-
145           internal.  It can be necessary for some low level toolchain
146           libraries like “libgcc”.
147
148       ignore-blacklist
149           A deprecated alias for allow-internal (since dpkg 1.20.1, supported
150           since dpkg 1.15.3).
151
152       c++ Denotes c++ symbol pattern. See Using symbol patterns subsection
153           below.
154
155       symver
156           Denotes symver (symbol version) symbol pattern. See Using symbol
157           patterns subsection below.
158
159       regex
160           Denotes regex symbol pattern. See Using symbol patterns subsection
161           below.
162
163   Using symbol patterns
164       Unlike a standard symbol specification, a pattern may cover multiple
165       real symbols from the library. dpkg-gensymbols will attempt to match
166       each pattern against each real symbol that does not have a specific
167       symbol counterpart defined in the symbol file. Whenever the first
168       matching pattern is found, all its tags and properties will be used as
169       a basis specification of the symbol. If none of the patterns matches,
170       the symbol will be considered as new.
171
172       A pattern is considered lost if it does not match any symbol in the
173       library. By default this will trigger a dpkg-gensymbols failure under
174       -c1 or higher level. However, if the failure is undesired, the pattern
175       may be marked with the optional tag. Then if the pattern does not match
176       anything, it will only appear in the diff as MISSING. Moreover, like
177       any symbol, the pattern may be limited to the specific architectures
178       with the arch tag. Please refer to Standard symbol tags subsection
179       above for more information.
180
181       Patterns are an extension of the deb-symbols(5) format hence they are
182       only valid in symbol file templates. Pattern specification syntax is
183       not any different from the one of a specific symbol. However, symbol
184       name part of the specification serves as an expression to be matched
185       against name@version of the real symbol. In order to distinguish among
186       different pattern types, a pattern will typically be tagged with a
187       special tag.
188
189       At the moment, dpkg-gensymbols supports three basic pattern types:
190
191       c++ This pattern is denoted by the c++ tag. It matches only C++ symbols
192           by their demangled symbol name (as emitted by c++filt(1) utility).
193           This pattern is very handy for matching symbols which mangled names
194           might vary across different architectures while their demangled
195           names remain the same. One group of such symbols is non-virtual
196           thunks which have architecture specific offsets embedded in their
197           mangled names. A common instance of this case is a virtual
198           destructor which under diamond inheritance needs a non-virtual
199           thunk symbol. For example, even if _ZThn8_N3NSB6ClassDD1Ev@Base on
200           32bit architectures will probably be _ZThn16_N3NSB6ClassDD1Ev@Base
201           on 64bit ones, it can be matched with a single c++ pattern:
202
203            libdummy.so.1 libdummy1 #MINVER#
204             [...]
205             (c++)"non-virtual thunk to NSB::ClassD::~ClassD()@Base" 1.0
206             [...]
207
208           The demangled name above can be obtained by executing the following
209           command:
210
211             $ echo '_ZThn8_N3NSB6ClassDD1Ev@Base' | c++filt
212
213           Please note that while mangled name is unique in the library by
214           definition, this is not necessarily true for demangled names. A
215           couple of distinct real symbols may have the same demangled name.
216           For example, that's the case with non-virtual thunk symbols in
217           complex inheritance configurations or with most constructors and
218           destructors (since g++ typically generates two real symbols for
219           them). However, as these collisions happen on the ABI level, they
220           should not degrade quality of the symbol file.
221
222       symver
223           This pattern is denoted by the symver tag. Well maintained
224           libraries have versioned symbols where each version corresponds to
225           the upstream version where the symbol got added. If that's the
226           case, you can use a symver pattern to match any symbol associated
227           to the specific version. For example:
228
229            libc.so.6 libc6 #MINVER#
230             (symver)GLIBC_2.0 2.0
231             [...]
232             (symver)GLIBC_2.7 2.7
233             access@GLIBC_2.0 2.2
234
235           All symbols associated with versions GLIBC_2.0 and GLIBC_2.7 will
236           lead to minimal version of 2.0 and 2.7 respectively with the
237           exception of the symbol access@GLIBC_2.0. The latter will lead to a
238           minimal dependency on libc6 version 2.2 despite being in the scope
239           of the "(symver)GLIBC_2.0" pattern because specific symbols take
240           precedence over patterns.
241
242           Please note that while old style wildcard patterns (denoted by
243           "*@version" in the symbol name field) are still supported, they
244           have been deprecated by new style syntax
245           "(symver|optional)version". For example, "*@GLIBC_2.0 2.0" should
246           be written as "(symver|optional)GLIBC_2.0 2.0" if the same
247           behaviour is needed.
248
249       regex
250           Regular expression patterns are denoted by the regex tag. They
251           match by the perl regular expression specified in the symbol name
252           field. A regular expression is matched as it is, therefore do not
253           forget to start it with the ^ character or it may match any part of
254           the real symbol name@version string. For example:
255
256            libdummy.so.1 libdummy1 #MINVER#
257             (regex)"^mystack_.*@Base$" 1.0
258             (regex|optional)"private" 1.0
259
260           Symbols like "mystack_new@Base", "mystack_push@Base",
261           "mystack_pop@Base" etc.  will be matched by the first pattern while
262           e.g. "ng_mystack_new@Base" won't.  The second pattern will match
263           all symbols having the string "private" in their names and matches
264           will inherit optional tag from the pattern.
265
266       Basic patterns listed above can be combined where it makes sense. In
267       that case, they are processed in the order in which the tags are
268       specified. For example, both:
269
270         (c++|regex)"^NSA::ClassA::Private::privmethod\d\(int\)@Base" 1.0
271         (regex|c++)N3NSA6ClassA7Private11privmethod\dEi@Base 1.0
272
273       will match symbols "_ZN3NSA6ClassA7Private11privmethod1Ei@Base" and
274       "_ZN3NSA6ClassA7Private11privmethod2Ei@Base". When matching the first
275       pattern, the raw symbol is first demangled as C++ symbol, then the
276       demangled name is matched against the regular expression. On the other
277       hand, when matching the second pattern, regular expression is matched
278       against the raw symbol name, then the symbol is tested if it is C++ one
279       by attempting to demangle it. A failure of any basic pattern will
280       result in the failure of the whole pattern.  Therefore, for example,
281       "__N3NSA6ClassA7Private11privmethod\dEi@Base" will not match either of
282       the patterns because it is not a valid C++ symbol.
283
284       In general, all patterns are divided into two groups: aliases (basic
285       c++ and symver) and generic patterns (regex, all combinations of
286       multiple basic patterns). Matching of basic alias-based patterns is
287       fast (O(1)) while generic patterns are O(N) (N - generic pattern count)
288       for each symbol.  Therefore, it is recommended not to overuse generic
289       patterns.
290
291       When multiple patterns match the same real symbol, aliases (first c++,
292       then symver) are preferred over generic patterns. Generic patterns are
293       matched in the order they are found in the symbol file template until
294       the first success.  Please note, however, that manual reordering of
295       template file entries is not recommended because dpkg-gensymbols
296       generates diffs based on the alphanumerical order of their names.
297
298   Using includes
299       When the set of exported symbols differ between architectures, it may
300       become inefficient to use a single symbol file. In those cases, an
301       include directive may prove to be useful in a couple of ways:
302
303       •   You can factorize the common part in some external file and include
304           that file in your package.symbols.arch file by using an include
305           directive like this:
306
307            #include "I<packages>.symbols.common"
308
309       •   The include directive may also be tagged like any symbol:
310
311            (tag|...|tagN)#include "file-to-include"
312
313           As a result, all symbols included from file-to-include will be
314           considered to be tagged with tag ... tagN by default. You can use
315           this feature to create a common package.symbols file which includes
316           architecture specific symbol files:
317
318             common_symbol1@Base 1.0
319            (arch=amd64 ia64 alpha)#include "package.symbols.64bit"
320            (arch=!amd64 !ia64 !alpha)#include "package.symbols.32bit"
321             common_symbol2@Base 1.0
322
323       The symbols files are read line by line, and include directives are
324       processed as soon as they are encountered. This means that the content
325       of the included file can override any content that appeared before the
326       include directive and that any content after the directive can override
327       anything contained in the included file. Any symbol (or even another
328       #include directive) in the included file can specify additional tags or
329       override values of the inherited tags in its tag specification.
330       However, there is no way for the symbol to remove any of the inherited
331       tags.
332
333       An included file can repeat the header line containing the SONAME of
334       the library. In that case, it overrides any header line previously
335       read.  However, in general it's best to avoid duplicating header lines.
336       One way to do it is the following:
337
338        #include "libsomething1.symbols.common"
339         arch_specific_symbol@Base 1.0
340

SEE ALSO

342       deb-symbols(5), dpkg-shlibdeps(1), dpkg-gensymbols(1).
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345
3461.21.9                            2022-07-01                deb-src-symbols(5)
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