From 6240129c6aea6033a60a39dbe0719b21ec3018ef Mon Sep 17 00:00:00 2001 From: Russ Allbery Date: Mon, 2 Jan 2012 13:44:41 -0800 Subject: [PATCH] First draft of symbols documentation Based heavily on the existing shlibs section and on the deb-symbols(5) manual page. The symbols section takes over as the default recommendation and shlibs moves one section later. Also includes more information about when to change the minimal version in the symbols file. --- policy.sgml | 1163 +++++++++++++++++++++++++++++++++------------------ 1 file changed, 766 insertions(+), 397 deletions(-) diff --git a/policy.sgml b/policy.sgml index 79281e9..cca4b6d 100644 --- a/policy.sgml +++ b/policy.sgml @@ -840,10 +840,11 @@ Among those files are the package maintainer scripts and control, the binary package control file that contains the control fields for - the package. Other control information files - include the shlibs - file used to store shared library dependency information - and the conffiles file that lists the package's + the package. Other control information files include + the symbols file + or shlibs file + used to store shared library dependency information and + the conffiles file that lists the package's configuration files (described in ).

@@ -5521,9 +5522,9 @@ Replaces: mail-transport-agent linked against the old shared library. Correct versioning of dependencies on the newer shared library by binaries that use the new interfaces is handled via - the shlibs - system or via symbols files (see - ). + the symbols system + or the shlibs + system.

@@ -5792,361 +5793,811 @@ Replaces: mail-transport-agent

- + Dependencies between the library and other packages - - the shlibs system + the symbols system

If a package contains a binary or library which links to a - shared library, we must ensure that when the package is - installed on the system, all of the libraries needed are - also installed. This requirement led to the creation of the - shlibs system, which is very simple in its design: - any package which provides a shared library also - provides information on the package dependencies required to - ensure the presence of this library, and any package which - uses a shared library uses this information to - determine the dependencies it requires. The files which - contain the mapping from shared libraries to the necessary - dependency information are called shlibs files. -

- -

- When a package is built which contains any shared libraries, it - must provide a shlibs file for other packages to - use. When a package is built which contains any shared - libraries or compiled binaries, it must run - dpkg-shlibdeps - on these to determine the libraries used and hence the - dependencies needed by this package. -

- dpkg-shlibdeps will use a program - like objdump or readelf to find - the libraries directly needed by the binaries or shared - libraries in the package. -

- -

- We say that a binary foo directly uses - a library libbar if it is explicitly linked - with that library (that is, the library is listed in the ELF - NEEDED attribute, caused by adding -lbar - to the link line when the binary is created). Other - libraries that are needed by libbar are linked - indirectly to foo, and the dynamic - linker will load them automatically when it loads - libbar. A package should depend on the libraries - it directly uses, but not the libraries it indirectly uses. - The dependencies for those libraries will automatically pull - in the other libraries. -

- -

- A good example of where this helps is the following. We - could update libimlib with a new version that - supports a new graphics format called dgf (but retaining the - same major version number) and depends on libdgf. - If we used ldd to add dependencies for every - library directly or indirectly linked with a binary, every - package that uses libimlib would need to be - recompiled so it would also depend on libdgf or it - wouldn't run due to missing symbols. Since dependencies are - only added based on ELF NEEDED attribute, packages - using libimlib can rely on libimlib itself - having the dependency on libdgf and so they would - not need rebuilding. -

+ shared library, we must ensure that, when the package is + installed on the system, all of the libraries needed are also + installed. These dependencies must be added to the binary + package when it is built, since they may change based on which + version of a shared library the binary or library was linnked + with. To allow these dependencies to be constructed, shared + libraries must provide either a symbols file or + a shlibs file, which provide information on the + package dependencies required to ensure the presence of this + library. Any package which uses a shared library must use these + files to determine the required dependencies when it is built. +

+ +

+ shlibs files were the original mechanism for + handling library dependencies. They are documented + in . symbols files, + documented in this section, are recommended for most packages, + since they provide dependency information for each exported + symbol and therefore generate more accurate dependencies for + binaries that do not use symbols from newer versions of the + shared library. However, shlibs files must be used + for udebs. Packages which provide a symbols file + are not required to provide a shlibs file. +

+ +

+ When a package that contains any shared libraries or compiled + binaries is built, it must run dpkg-shlibdeps on + each shared library and compiled binary to determine the + libraries used and hence the dependencies needed by the + package. + dpkg-shlibdeps will use a program + like objdump or readelf to find the + libraries and the symbols in those libraries directly needed + by the binaries or shared libraries in the package.

- In the following sections, we will first describe where the - various shlibs files are to be found, then how to - use dpkg-shlibdeps, and finally the shlibs - file format and how to create them if your package contains a - shared library. + We say that a binary foo directly uses a + library libbar if it is explicitly linked with that + library (that is, the library is listed in the + ELF NEEDED attribute, caused by adding -lbar + to the link line when the binary is created). Other libraries + that are needed by libbar are + linked indirectly to foo, and the dynamic + linker will load them automatically when it + loads libbar. A package should depend on the libraries + it directly uses, but not the libraries it indirectly uses. The + dependencies for those libraries will automatically pull in the + other libraries. dpkg-shlibdeps will handle this + logic automatically, but package maintainers need to be aware of + this distinction between directly and indirectly using a library + if they have to override its results for some reason. + + A good example of where this helps is the following. We could + update libimlib with a new version that supports a + new graphics format called dgf (but retaining the same major + version number) and depends on libdgf. If we + used ldd to add dependencies for every library + directly or indirectly linked with a binary, every package + that uses libimlib would need to be recompiled so it + would also depend on libdgf or it wouldn't run due to + missing symbols. Since dependencies are only added based on + ELF NEEDED attribute, packages + using libimlib can rely on libimlib itself + having the dependency on libdgf and so they would not + need rebuilding. +

- - The shlibs files present on the system -

- There are several places where shlibs files are - found. The following list gives them in the order in which - they are read by - dpkg-shlibdeps. - (The first one which gives the required information is used.) + In the following sections, we will first describe where the + various symbols files are to be found, then how to + use dpkg-shlibdeps, and finally + the symbols file format and how to create them if + your package contains a shared library.

-

- - -

debian/shlibs.local

- -

- This lists overrides for this package. This file should - normally not be used, but may be needed temporarily in - unusual situations to work around bugs in other packages, - or in unusual cases where the normally declared dependency - information in the installed shlibs file for - a library cannot be used. This file overrides information - obtained from any other source. -

- + + The symbols files present on the + system - -

/etc/dpkg/shlibs.override

+

+ symbols files for a shared library are normally + provided by the shared library package, but there are several + override paths that are checked first in case that information + is wrong or missing. The following list gives them in the + order in which they are read by dpkg-shlibdeps + The first one that contains the required information is used. + + +

debian/*/DEBIAN/symbols

-

- This lists global overrides. This list is normally - empty. It is maintained by the local system - administrator. -

- +

+ During the package build, if the package itself contains + shared libraries with symbols files, they + will be generated in these staging directories + by dpkg-gensymbols. symbols + files found in the build tree take precedence + over symbols files from other binary + packages. +

- -

DEBIAN/shlibs files in the "build directory"

+

+ These files must exist + before dpkg-shlibdeps is run or the + dependencies of binaries and libraries from a source + package on other libraries from that same source package + will not be correct. In practice, this means + that dpkg-gensymbols must be run + before dpkg-shlibdeps during the package + build. + An example may clarify. Suppose the source + package foo generates two binary + packages, libfoo2 and foo-runtime. + When building the binary packages, the contents of the + packages are staged in the + directories debian/libfoo2 + and debian/foo-runtime respectively. + (debian/tmp could be used instead of one + of these.) Since libfoo2 provides + the libfoo shared library, it will contain + a symbols file, which will be installed + in debian/libfoo2/DEBIAN/symbols, + eventually to be included as a control file in that + package. When dpkg-shlibdeps is run on + the + executable debian/foo-runtime/usr/bin/foo-prog, + it will examine + the debian/libfoo2/DEBIAN/symbols file to + determine whether foo-prog's library + dependencies are satisfied by any of the libraries + provided by libfoo2. Since those binaries + were linked against the just-built shared library as + part of the build process, the symbols + file for the newly-built libfoo2 must take + precedence over a symbols file for any + other libfoo2 package already installed on + the system. + +

+ -

- When packages are being built, - any debian/shlibs files are copied into the - control information file area of the temporary build - directory and given the name shlibs. These - files give details of any shared libraries included in the - same package. - An example may help here. Let us say that the source - package foo generates two binary - packages, libfoo2 and foo-runtime. - When building the binary packages, the two packages are - created in the directories debian/libfoo2 - and debian/foo-runtime respectively. - (debian/tmp could be used instead of one of - these.) Since libfoo2 provides the - libfoo shared library, it will require a - shlibs file, which will be installed in - debian/libfoo2/DEBIAN/shlibs, eventually to - become /var/lib/dpkg/info/libfoo2.shlibs. - When dpkg-shlibdeps is run on the - executable debian/foo-runtime/usr/bin/foo-prog, - it will examine - the debian/libfoo2/DEBIAN/shlibs file to - determine whether foo-prog's library - dependencies are satisfied by any of the libraries - provided by libfoo2. For this reason, - dpkg-shlibdeps must only be run once all of - the individual binary packages' shlibs files - have been installed into the build directory. - -

- + +

+ /etc/dpkg/symbols/package.symbols.arch + and /etc/dpkg/symbols/package.symbols +

- -

/var/lib/dpkg/info/*.shlibs

+

+ Per-system overrides of shared library dependencies. + These files normally do not exist. They are maintained + by the local system administrator and must not be + created by any Debian package. +

+ -

- These are the shlibs files corresponding to - all of the packages installed on the system, and are - maintained by the relevant package maintainers. -

- + +

symbols control files for packages + installed on the system

- -

/etc/dpkg/shlibs.default

+

+ The symbols control files for all the + packages currently installed on the system are searched + last. This will be the most common source of shared + library dependency information. These are normally + found in /var/lib/dpkg/info/*.symbols, but + packages should not rely on this and instead should + use dpkg-query --control-path package + symbols if for some reason these files need to be + examined. +

+ + +

-

- This file lists any shared libraries whose packages - have failed to provide correct shlibs files. - It was used when the shlibs setup was first - introduced, but it is now normally empty. It is - maintained by the dpkg maintainer. -

- - -

- +

+ Be aware that if a debian/shlibs.local exists in + the source package, it will override any symbols + files. This is the only case where a shlibs is + used despite symbols files being present. See + and + for more information. +

+ - - How to use dpkg-shlibdeps and the - shlibs files + + How to use dpkg-shlibdeps and the + symbols files -

- Put a call to - dpkg-shlibdeps - into your debian/rules file. If your package - contains only compiled binaries and libraries (but no scripts), - you can use a command such as: - +

+ If your package contains any compiled binaries or shared + libraries, put a call to dpkg-shlibdeps into + your debian/rules file in the source package. + List all of the compiled binaries, libraries, or loadable + modules in your package. If your source package builds only a + single binary package that contains only compiled binaries and + libraries (but no scripts) and is not multiarch, you can use a + command such as: + dpkg-shlibdeps debian/tmp/usr/bin/* debian/tmp/usr/sbin/* \ debian/tmp/usr/lib/* - - Otherwise, you will need to explicitly list the compiled - binaries and libraries. - If you are using debhelper, the - dh_shlibdeps program will do this work for you. - It will also correctly handle multi-binary packages. - -

+ + but normally finding all of the binaries is more + complex. + The easiest way to do this is to use a package helper + framework such as debhelper. If you are + using debhelper, the dh_shlibdeps + program will do this work for you. It will also correctly + handle multi-binary packages. + +

-

- This command puts the dependency information into the - debian/substvars file, which is then used by - dpkg-gencontrol. You will need to place a - ${shlibs:Depends} variable in the Depends - field in the control file for this to work. -

+

+ This command puts the dependency information into + the debian/substvars file, which is then used + by dpkg-gencontrol. You will need to place + a ${shlibs:Depends} variable in the Depends + field in the control file of every binary package built by + this source package that contains compiled binaries, + libraries, or loadable modules. If you have multiple binary + packages, you will need to call dpkg-shlibdeps on + each one which contains compiled libraries or binaries, using + the -T option to the dpkg utilities to + specify a different substvars file for each + binary package. + Again, dh_shlibdeps + and dh_gencontrol will handle all of this for + you if you're using debhelper. + +

-

- If you have multiple binary packages, you will need to call - dpkg-shlibdeps on each one which contains - compiled libraries or binaries. In such a case, you will - need to use the -T option to the dpkg - utilities to specify a different substvars file. -

+

+ For more details on dpkg-shlibdeps, + see . +

+ -

- If you are creating a udeb for use in the Debian Installer, - you will need to specify that dpkg-shlibdeps - should use the dependency line of type udeb by - adding the -tudeb option - dh_shlibdeps from the debhelper suite - will automatically add this option if it knows it is - processing a udeb. - . If there is no dependency line of - type udeb in the shlibs - file, dpkg-shlibdeps will fall back to the regular - dependency line. -

+ + The symbols File Format -

- For more details on dpkg-shlibdeps, please see - and - . -

- +

+ The following documents the format of the symbols + control file as included in binary packages. These files are + built from template symbols files in the source + package by dpkg-gensymbols. The template files + support a richer syntax that + allows dpkg-gensymbols to do some of the tedious + work involved in maintaining symbols files, such + as handling C++ symbols or optional symbols that may not exist + on particular architectures. When + writing symbols files for a shared library + package, refer to + for the richer syntax. +

- - The shlibs File Format +

+ A symbols may contain one or more entries, one + for each shared library contained in the package corresponding + to that symbols. Each entry has the following + format: +

-

- Each shlibs file has the same format. Lines - beginning with # are considered to be comments and - are ignored. Each line is of the form: - -[type: ]library-name soname-version dependencies ... - -

+

+ +library-soname main-dependency-template +[ | alternative-dependency-template ] +[ ... ] +[ * field-name: field-value ] +[ ... ] + symbol minimal-version[ id-of-dependency-template ] + +

-

- We will explain this by reference to the example of the - zlib1g package, which (at the time of writing) - installs the shared library /usr/lib/libz.so.1.1.3. -

+

+ To explain this format, we'll use the the zlib1g + package as an example, which (at the time of writing) installs + the shared library /usr/lib/libz.so.1.2.3.4. + Mandatory lines will be described first, followed by optional + lines. +

-

- type is an optional element that indicates the type - of package for which the line is valid. The only type currently - in use is udeb. The colon and space after the type are - required. -

+

+ library-soname must contain exactly the value of + the ELF SONAME attribute of the shared library. In + our example, this is libz.so.1. + This can be determined by using the command + +readelf -d /usr/lib/libz.so.1.2.3.4 | grep SONAME + + +

-

- library-name is the name of the shared library, - in this case libz. (This must match the name part - of the soname, see below.) -

+

+ main-dependency-template has the same syntax as a + dependency field in a binary package control file, except that + the string #MINVER# is replaced by a version + restriction like (>= version) or by + nothing if an unversioned dependency is deemed sufficient. + The version restriction will be based on which symbols from + the shared library are referenced and the version at which + they were introduced (see below). In nearly all + cases, main-dependency-template will + be package #MINVER#, + where package is the name of the binary package + containing the shared library. This adds a simple, + possibly-versioned dependency on the shared library package. + In some rare cases, such as when multiple packages provide the + same shared library ABI, the dependency template may need to + be more complex. +

-

- soname-version is the version part of the soname of - the library. The soname is the thing that must exactly match - for the library to be recognized by the dynamic linker, and is - usually of the form - name.so.major-version, in our - example, libz.so.1. - This can be determined using the command +

+ In our example, the first line of + the zlib1g symbols file would be: -objdump -p /usr/lib/libz.so.1.1.3 | grep SONAME +libz.so.1 zlib1g #MINVER# - - The version part is the part which comes after - .so., so in our case, it is 1. The soname may - instead be of the form - name-major-version.so, such - as libdb-4.8.so, in which case the name would - be libdb and the version would be 4.8. -

+

+ +

+ Each public symbol exported by the shared library must have a + corresponding symbol line, indented by one + space. symbol is the exported symbol (which, for + C++, means the mangled symbol) followed by @ and the + symbol version, or the string Base if there is no + symbol version. minimal-version is the most recent + version of the shared library that changed the behavior of + that symbol, whether by adding it, changing its function + signature (the parameters, their types, or the return type), + or its behavior in a way that is visible to a + caller. id-of-dependency-template is an optional + field that references + an alternative-dependency-template; see below for a + full description. +

+ +

+ For example, libz.so.1 contains the + symbols compress + and compressBound. compress has no symbol + version and last changed its behavior in upstream + version 1:1.1.4. compressBound has the + symbol version ZLIB_1.2.0, was introduced in upstream + version 1:1.2.0, and has not changed its behavior. + Its symbols file therefore contains the lines: + + compress@Base 1:1.1.4 + compressBound@ZLIB_1.2.0 1:1.2.0 + + Packages using only compress would then get a + dependency of zlib1g (>= 1:1.1.4), but packages + using compressBound would get a dependency + of zlib1g (>= 1:1.2.0). +

+ +

+ One or more alternative-dependency-template lines + may be provided. These are used in cases where some symbols + in the shared library should use one dependency template while + others should use a different template. The alternative + dependency templates are used only if a symbol line contains + the id-of-dependency-template field. The first + alternative dependency template is numbered 1, the second 2, + and so forth. + An example of where this may be needed is with a library + that implements the libGL interface. All GL implementations + provide the same set of base interfaces, and then may + provide some additional interfaces only used by programs + that require that specific GL implementation. So, for + example, libgl1-mesa-glx may use the + following symbols file: + +libGL.so.1 libgl1 +| libgl1-mesa-glx #MINVER# + publicGlSymbol@Base 6.3-1 + [...] + implementationSpecificSymbol@Base 6.5.2-7 1 + [...] + + Binaries or shared libraries using + only publicGlSymbol would depend only + on libgl1 (which may be provided by multiple + packages), but ones + using implementationSpecificSymbol would get a + dependency on libgl1-mesa-glx (>= 6.5.2-7) + +

+ +

+ Finally, the entry for the library may contain one or more + metadata fields. Currently, the only + supported field-name + is Build-Depends-Package, whose value lists + the library development + package on which packages using this shared library + declare a build dependency. If this field is + present, dpkg-shlibdeps uses it to ensure that + the resulting binary package dependency on the shared library + is at least as strict as the source package dependency on the + shared library development package. + This field should normally not be necessary, since if the + behavior of any symbol has changed, the corresponding + symbol minimal-version should have been + increased. But including it makes the symbols + system more robust by tightening the dependency in cases + where the package using the shared library specifically + requires at least a particular version of the shared library + development package for some reason. + + For our example, the zlib1g symbols file + would contain: + + * Build-Depends-Package: zlib1g-dev + + (Don't forget the leading space.) +

+ +

+ Also see . +

+ + + + Providing a symbols file + +

+ If your package provides a shared library, you should arrange + to include a symbols control file following the + format described above in that package. You must include + either a symbols control file or + a shlibs control file. +

+ +

+ Normally, this is done by creating a symbols in + the source package + named debian/package.symbols + or debian/symbols, possibly + with .arch appended if the symbols + information varies by architecture. This file may use the + extended syntax documented + in . Then, + call dpkg-gensymbols as part of the package build + process. It will create symbols files in the + package staging area based on the binaries and libraries in + the package staging area and the symbols files in + the source package. + If you are + using debhelper, dh_makeshlibs will + take care of calling either dpkg-gensymbols + or generating a shlibs file as appropriate. + +

+ +

+ Packages that provide symbols files must keep + them up-to-date to ensure correct dependencies in packages + that use the shared libraries. This means updating + the symbols file whenever a new public symbol is + added, changing the minimal-version field whenever + a symbol changes behavior or signature, and changing + the library-soname + and main-dependency-template, and probably all of + the minimal-version fields, when the library + changes SONAME. Removing a public symbol from + the symbols file because it's no longer provided + by the library normally requires changing the SONAME + of the library. See . +

+ +

+ Special care should be taken in updating + the minimal-version field when the behavior of a + public symbol changes. This is easy to neglect, since there + is no automated method of determining such changes, but + failing to update minimal-version in this case may + result in binary packages with too-weak dependencies that will + fail at runtime, possibly in ways that can cause security + vulnerabilities. If the package maintainer believes that a + symbol behavior change may have occurred but isn't sure, it's + safer to update the minimal-version of all possibly + affected symbols to the current upstream version rather than + leave them unmodified. This may result in unnecessarily + strict dependencies, but it ensures that packages whose + dependencies are satisfied will work properly. +

+ +

+ A common example of when a change + to minimal-version is required is a function that + takes an enum or struct argument that controls what the + function does. For example: + +enum library_op { OP_FOO, OP_BAR }; +int library_do_operation(enum library_op); + + If a new operation, OP_BAZ, is added, + the minimal-version + of library_do_operation must be increased to the + version at which OP_BAZ was introduced. Otherwise, a + binary built against the new version of the library (having + detected at compile-time that the library + supports OP_BAZ) may be installed with a shared + library that doesn't support OP_BAZ and will fail at + runtime when it tries to pass OP_BAZ into this + function. +

+ +

+ The minimal-version field normally should not + contain the Debian revision of the package, since the library + behavior is normally fixed for a particular upstream version + and any Debian packaging of that upstream version will have + the same behavior. In the rare case that the library behavior + was changed in a particular Debian revision, + appending ~ to the end of + the minimal-version that includes the Debian + revision is recommended, since this allows backports of the + shared library package using the normal backport versioning + convention to satisfy the dependency. +

+ + + + + Dependencies between the library and other packages - + the shlibs system

- dependencies has the same syntax as a dependency - field in a binary package control file. It should give - details of which packages are required to satisfy a binary - built against the version of the library contained in the - package. See for details. + The shlibs system is an alternative to + the symbols system for declaring dependencies for + shared libraries. It predated the symbols system and + is therefore frequently seen in older packages. It is also + required for udebs, which do not support symbols.

- In our example, if the first version of the zlib1g - package which contained a minor number of at least - 1.3 was 1:1.1.3-1, then the - shlibs entry for this library could say: - -libz 1 zlib1g (>= 1:1.1.3) - - The version-specific dependency is to avoid warnings from - the dynamic linker about using older shared libraries with - newer binaries. + shlibs files do not provide as detailed of + information as symbols files. They only provide + information about the library as a whole, not individual + symbols, and therefore have to force tighter dependencies since + they have no way of relaxing dependencies for binaries and + libraries that only use symbols whose behavior has not changed. + Because of this, and because of some problems with + how shlibs files represent the + library SONAME, symbols files are + recommended instead for any shared library package that isn't a + udeb.

- As zlib1g also provides a udeb containing the shared library, - there would also be a second line: - -udeb: libz 1 zlib1g-udeb (>= 1:1.1.3) - + In the following sections, we will first describe where the + various shlibs files are to be found, then how to + use dpkg-shlibdeps, and finally + the shlibs file format and how to create them if + your package contains a shared library. Much of the information + about shlibs files is the same as + for symbols files, so only the differences will be + mentioned.

- - - Providing a shlibs file + + The shlibs files present on the + system -

- If your package provides a shared library, you need to create - a shlibs file following the format described above. - It is usual to call this file debian/shlibs (but if - you have multiple binary packages, you might want to call it - debian/shlibs.package instead). Then - let debian/rules install it in the control - information file area: - +

+ There are several places where shlibs files are + found. The following list gives them in the order in which + they are read by dpkg-shlibdeps. (The first one + which gives the required information is used.) + + +

debian/shlibs.local

+ +

+ This lists overrides for this package. This file should + normally not be used, but may be needed temporarily in + unusual situations to work around bugs in other + packages, or in unusual cases where the normally + declared dependency information in the + installed shlibs file for a library cannot + be used. This file overrides information obtained from + any other source. +

+ + + +

/etc/dpkg/shlibs.override

+ +

+ This lists global overrides. This list is normally + empty. It is maintained by the local system + administrator. +

+ + + +

DEBIAN/shlibs files in the "build + directory"

+ +

+ When packages are being built, + any debian/shlibs files are copied into the + control information file area of the temporary build + directory and given the name shlibs. These + files give details of any shared libraries included in + the same package. +

+ + + +

shlibs control files for packages + installed on the system

+ +

+ The shlibs control files for all the + packages currently installed on the system. These are + normally found + in /var/lib/dpkg/info/*.symbols, but + packages should not rely on this and instead should + use dpkg-query --control-path package + shlibs if for some reason these files need to be + examined. +

+ + + +

/etc/dpkg/shlibs.default

+ +

+ This file lists any shared libraries whose packages have + failed to provide correct shlibs files. It + was used when the shlibs setup was first + introduced, but it is now normally empty. It is + maintained by the dpkg maintainer. +

+ + +

+ +

+ If a symbols file for a shared library package + is available, dpkg-shlibdeps will always use it + in preference to a shlibs, with the exception + of debian/shlibs.local. The latter overrides any + other shlibs or symbols files. +

+ + + + How to use dpkg-shlibdeps and the + shlibs files + +

+ Use of dpkg-shlibdeps with shlibs + files is generally the same as with symbols + files. See . +

+ +

+ If you are creating a udeb for use in the Debian Installer, + you will need to specify that dpkg-shlibdeps + should use the dependency line of type udeb by + adding the -tudeb option + dh_shlibdeps from the debhelper suite + will automatically add this option if it knows it is + processing a udeb. + . If there is no dependency line of + type udeb in the shlibs + file, dpkg-shlibdeps will fall back to the + regular dependency line. +

+ + + + The shlibs File Format + +

+ Each shlibs file has the same format. Lines + beginning with # are considered to be comments and + are ignored. Each line is of the form: + +[type: ]library-name soname-version dependencies ... + +

+ +

+ We will explain this by reference to the example of the + zlib1g package, which (at the time of writing) + installs the shared + library /usr/lib/libz.so.1.2.3.4. +

+ +

+ type is an optional element that indicates the type + of package for which the line is valid. The only type + currently in use is udeb. The colon and space after + the type are required. +

+ +

+ library-name is the name of the shared library, in + this case libz. (This must match the name part of + the soname, see below.) +

+ +

+ soname-version is the version part of the + ELF SONAME attribute of the library. + The SONAME is the thing that must exactly match for + the library to be recognized by the dynamic linker, and is + usually of the + form name.so.major-version, in + our example, libz.so.1. + The version part is the part which comes after + .so., so in our case, it is 1. The soname + may instead be of the + form name-major-version.so, + such as libdb-5.1.so, in which case the name would + be libdb and the version would be 5.1. +

+ +

+ dependencies has the same syntax as a dependency + field in a binary package control file. It should give + details of which packages are required to satisfy a binary + built against the version of the library contained in the + package. See for details. +

+ +

+ In our example, if the last change to the zlib1g + package that could change behavior for a client of that + library was in version 1:1.2.3.3.dfsg-1, then + the shlibs entry for this library could say: + +libz 1 zlib1g (>= 1:1.2.3.3.dfsg-1) + + This version restriction must be new enough that any binary + built against the current version of the library will work + with any version of the shared library that satisfies that + dependency. +

+ +

+ As zlib1g also provides a udeb containing the shared library, + there would also be a second line: + +udeb: libz 1 zlib1g-udeb (>= 1:1.2.3.3.dfsg-1) + +

+ + + + Providing a shlibs file + +

+ If your package provides a shared library, you need to create + a shlibs file following the format described + above. It is usual to call this + file debian/shlibs (but if you have multiple + binary packages, you might want to call + it debian/package.shlibs instead). + Then let debian/rules install it in the control + information file area: + install -m644 debian/shlibs debian/tmp/DEBIAN - - or, in the case of a multi-binary package: - -install -m644 debian/shlibs.package debian/package/DEBIAN/shlibs - - An alternative way of doing this is to create the - shlibs file in the control information file area - directly from debian/rules without using - a debian/shlibs file at all, - This is what dh_makeshlibs in - the debhelper suite does. If your package - also has a udeb that provides a shared - library, dh_makeshlibs can automatically generate - the udeb: lines if you specify the name of the udeb - with the --add-udeb option. - - since the debian/shlibs file itself is ignored by - dpkg-shlibdeps. -

+ + or, in the case of a multi-binary package: + +install -m644 debian/package.shlibs debian/package/DEBIAN/shlibs + + An alternative way of doing this is to create + the shlibs file in the control information file + area directly from debian/rules without using + a debian/shlibs file at all, + This is what dh_makeshlibs in + the debhelper suite does. If your package + also has a udeb that provides a shared + library, dh_makeshlibs can automatically + generate the udeb: lines if you specify the name of + the udeb with the --add-udeb option. + + since the debian/shlibs file itself is ignored by + dpkg-shlibdeps. +

-

- As dpkg-shlibdeps reads the - DEBIAN/shlibs files in all of the binary packages - being built from this source package, all of the - DEBIAN/shlibs files should be installed before - dpkg-shlibdeps is called on any of the binary - packages. -

- +

+ Since dpkg-shlibdeps reads + the DEBIAN/shlibs files in all of the binary + packages being built from this source package, all of + the DEBIAN/shlibs files should be installed + before dpkg-shlibdeps is called on any of the + binary packages. +

+ @@ -7702,8 +8153,9 @@ INSTALL = install -s # (or use strip on the files in debian/tmp) Although not enforced by the build tools, shared libraries must be linked against all libraries that they use symbols from in the same way that binaries are. This ensures the correct - functioning of the shlibs - system and guarantees that all libraries can be safely opened + functioning of the symbols + and shlibs + systems and guarantees that all libraries can be safely opened with dlopen(). Packagers may wish to use the gcc option -Wl,-z,defs when building a shared library. Since this option enforces symbol resolution at build time, @@ -10481,89 +10933,6 @@ END-INFO-DIR-ENTRY dpkg-genchanges.

- - - dpkg-shlibdeps - calculates shared library - dependencies - - -

- This program is usually called from debian/rules - just before dpkg-gencontrol (see ), in the top level of the source tree. -

- -

- Its arguments are executables and shared libraries - -

- They may be specified either in the locations in the - source tree where they are created or in the locations - in the temporary build tree where they are installed - prior to binary package creation. -

- for which shared library dependencies should - be included in the binary package's control file. -

- -

- If some of the found shared libraries should only - warrant a Recommends or Suggests, or if - some warrant a Pre-Depends, this can be achieved - by using the -ddependency-field option - before those executable(s). (Each -d option - takes effect until the next -d.) -

- -

- dpkg-shlibdeps does not directly cause the - output control file to be modified. Instead by default it - adds to the debian/substvars file variable - settings like shlibs:Depends. These variable - settings must be referenced in dependency fields in the - appropriate per-binary-package sections of the source - control file. -

- -

- For example, a package that generates an essential part - which requires dependencies, and optional parts that - which only require a recommendation, would separate those - two sets of dependencies into two different fields. - At the time of writing, an example for this was the - - It can say in its debian/rules: - - dpkg-shlibdeps -dDepends program anotherprogram ... \ - -dRecommends optionalpart anotheroptionalpart - - and then in its main control file debian/control: - - ... - Depends: ${shlibs:Depends} - Recommends: ${shlibs:Recommends} - ... - -

- -

- Sources which produce several binary packages with - different shared library dependency requirements can use - the -pvarnameprefix option to override - the default shlibs: prefix (one invocation of - dpkg-shlibdeps per setting of this option). - They can thus produce several sets of dependency - variables, each of the form - varnameprefix:dependencyfield, - which can be referred to in the appropriate parts of the - binary package control files. -

- - - dpkg-distaddfile - adds a file to -- 2.39.2