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diff --git a/man/deb-src-symbols.man b/man/deb-src-symbols.man new file mode 100644 index 000000000..e1fc836fb --- /dev/null +++ b/man/deb-src-symbols.man @@ -0,0 +1,348 @@ +.\" dpkg manual page - deb-src-symbols(5) +.\" +.\" Copyright © 2007-2011 Raphaël Hertzog <hertzog@debian.org> +.\" Copyright © 2009-2010 Modestas Vainius <modestas@vainius.eu> +.\" Copyright © 2012-2015 Guillem Jover <guillem@debian.org> +.\" +.\" This is free software; you can redistribute it and/or modify +.\" it under the terms of the GNU General Public License as published by +.\" the Free Software Foundation; either version 2 of the License, or +.\" (at your option) any later version. +.\" +.\" This is distributed in the hope that it will be useful, +.\" but WITHOUT ANY WARRANTY; without even the implied warranty of +.\" MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the +.\" GNU General Public License for more details. +.\" +.\" You should have received a copy of the GNU General Public License +.\" along with this program. If not, see <https://www.gnu.org/licenses/>. +. +.TH deb\-src\-symbols 5 "%RELEASE_DATE%" "%VERSION%" "dpkg suite" +.nh +.SH NAME +deb\-src\-symbols \- Debian's extended shared library template file +. +.SH SYNOPSIS +debian/\fIpackage\fR.symbols.\fIarch\fR +.br +debian/symbols.\fIarch\fR +.br +debian/\fIpackage\fR.symbols +.br +debian/symbols +. +.SH DESCRIPTION +The symbol file templates are shipped in Debian source packages, and its +format is a superset of the symbols files shippsed in binary packages. +.P +.SS 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 \fBUsing includes\fP). +Lines starting with ‘#MISSING:’ are special comments documenting +symbols that have disappeared. +.SS Using #PACKAGE# substitution +.P +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 \fI#PACKAGE#\fR. It will be replaced by the real package +name during installation of the symbols files. Contrary to the +\fI#MINVER#\fR marker, \fI#PACKAGE#\fR will never appear in a symbols file +inside a binary package. +.SS Using symbol tags +.P +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 +\fBdpkg\-gensymbols\fR and trigger special handling of the symbols. See +subsection \fBStandard symbol tags\fR for reference of these tags. +.P +Tag specification comes right before the symbol name (no whitespace is allowed +in between). It always starts with an opening bracket \fB(\fR, ends with a +closing bracket \fB)\fR and must contain at least one tag. Multiple tags are +separated by the \fB|\fR character. Each tag can optionally have a value which +is separated form the tag name by the \fB=\fR character. Tag names and values +can be arbitrary strings except they cannot contain any of the special \fB)\fR +\fB|\fR \fB=\fR characters. Symbol names following a tag specification can +optionally be quoted with either \fB'\fR or \fB"\fR 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. +.P + (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 +.P +The first symbol in the example is named \fItagged quoted symbol\fR and has two +tags: \fItag1\fR with value \fIi am marked\fR and \fItag name with space\fR +that has no value. The second symbol named \fItagged_unquoted_symbol\fR is +only tagged with the tag named \fIoptional\fR. The last symbol is an +example of the normal untagged symbol. +.P +Since symbol tags are an extension of the \fBdeb\-symbols\fP(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 +\fBdpkg\-gensymbols\fR is called without the \fB\-t\fP option, it will +output symbols files compatible to the \fBdeb\-symbols\fP(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 +(\fB\-t\fP) 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. +.SS Standard symbol tags +.TP +.B optional +A symbol marked as optional can disappear from the library at any time and that +will never cause \fBdpkg\-gensymbols\fR 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. +.TP +.B arch=\fIarchitecture-list\fR +.TQ +.B arch\-bits=\fIarchitecture-bits\fR +.TQ +.B arch\-endian=\fIarchitecture-endianness\fR +These tags allow one to restrict the set of architectures where the symbol +is supposed to exist. The \fBarch\-bits\fP and \fBarch\-endian\fP 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 \fBdpkg\-gensymbols\fR 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 \fIarchitecture-list\fR is the same as the one used in the +\fBBuild\-Depends\fP field of \fIdebian/control\fR (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 \fIarchitecture-bits\fP is either \fB32\fP or \fB64\fP. + + (arch-bits=32)32bit_specific_symbol@Base 1.0 + (arch-bits=64)64bit_specific_symbol@Base 1.0 + +The \fIarchitecture-endianness\fP is either \fBlittle\fP or \fBbig\fP. + + (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 +.TP +.B 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 \fBignore\-blacklist\fP. It can be necessary for +some low level toolchain libraries like libgcc. +.TP +.B c++ +Denotes \fIc++\fR symbol pattern. See \fBUsing symbol patterns\fR subsection +below. +.TP +.B symver +Denotes \fIsymver\fR (symbol version) symbol pattern. See \fBUsing symbol +patterns\fR subsection below. +.TP +.B regex +Denotes \fIregex\fR symbol pattern. See \fBUsing symbol patterns\fR subsection +below. +.SS Using symbol patterns +.P +Unlike a standard symbol specification, a pattern may cover multiple real +symbols from the library. \fBdpkg\-gensymbols\fR will attempt to match each +pattern against each real symbol that does \fInot\fR 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 \fBdpkg\-gensymbols\fP failure under \fB\-c1\fP or +higher level. However, if the failure is undesired, the pattern may be marked +with the \fIoptional\fR 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 \fIarch\fR tag. Please +refer to \fBStandard symbol tags\fR subsection above for more information. + +Patterns are an extension of the \fBdeb\-symbols\fP(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 \fIname@version\fR +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, \fBdpkg\-gensymbols\fR supports three basic pattern types: +.TP 3 +.B c++ +This pattern is denoted by the \fIc++\fR tag. It matches only C++ symbols by +their demangled symbol name (as emitted by \fBc++filt\fR(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 \fInon\-virtual thunks\fR 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 \fIc++\fR 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. +.TP +.B symver +This pattern is denoted by the \fIsymver\fR 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 \fIsymver\fR 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. +.TP +.B regex +Regular expression patterns are denoted by the \fIregex\fR 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 +\fI^\fR character or it may match any part of the real symbol +\fIname@version\fR 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 e.g. "ng_mystack_new@Base" won't. +The second pattern will match all symbols having the string "private" in their +names and matches will inherit \fIoptional\fR tag from the pattern. +.P +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 \fIc++\fR +and \fIsymver\fR) and generic patterns (\fIregex\fR, 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 \fIc++\fR, +then \fIsymver\fR) 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 \fBdpkg\-gensymbols\fR generates diffs based on the +alphanumerical order of their names. +.SS Using includes +.P +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: +.IP • 4 +You can factorize the common part in some external file +and include that file in your \fIpackage\fR.symbols.\fIarch\fR file by +using an include directive like this: + +#include "\fIpackages\fR.symbols.common" +.IP • +The include directive may also be tagged like any symbol: + +(tag|...|tagN)#include "file-to-include" + +As a result, all symbols included from \fIfile-to-include\fR will be considered +to be tagged with \fItag\fR ... \fItagN\fR by default. You can use this feature +to create a common \fIpackage\fR.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 +.P +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. +.P +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: +.PP +#include "libsomething1.symbols.common" + arch_specific_symbol@Base 1.0 +.SH SEE ALSO +.BR deb\-symbols (5), +.BR dpkg\-shlibdeps (1), +.BR dpkg\-gensymbols (1). |