From b19fb874de1a4913125c5be18b244e596cf7e847 Mon Sep 17 00:00:00 2001 From: Jonathan Nieder Date: Sun, 12 Aug 2012 13:43:50 -0700 Subject: [PATCH] Clarifications to symbols and shlibs policy subject/verb agreement: s/provide/provides/ Packages with libraries or binaries linking to a shared library must use symbols or shlibs files to compute their dependencies. Packages that dlopen() a shared library should do so as well, but since that is not typical practice and the tools to do that don't exist, it is not made a policy "must" yet. The minimal version for a symbol can be bumped after the version of the package in which the symbol was introduced. Add a footnote explaining why shlibs files cannot be used for libraries with unusual sonames. The shlibs file for a library udeb goes in the corresponding deb. The library deb corresponding to a udeb is supposed to provide a shlibs file, rather than consuming (using) one. Add "for example" when talking about dpkg-shlibdeps -T. This is just an illustration and not meant to be normative. If a library is used both directly and indirectly, the direct dependency still needs to be declared. Backward-compatibility is defined in terms of what reasonable programs and libraries need. In the normal case, symbols files go in dpkg's admindir as package control files. wording fix: "dependency on" avoids some of the ambiguity in "dependency of". --- policy.sgml | 92 +++++++++++++++++++++++++++++------------------------ 1 file changed, 51 insertions(+), 41 deletions(-) diff --git a/policy.sgml b/policy.sgml index 6cb5b0d..0965b76 100644 --- a/policy.sgml +++ b/policy.sgml @@ -5978,25 +5978,30 @@ Built-Using: grub2 (= 1.99-9), loadlin (= 1.6e-1) whether new library interfaces are available and can be called). 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. -

- -

- These two mechanisms differ in the degree of detail that they - provide. A symbols file documents every symbol - that is part of the library ABI and, for each, the version of - the package in which it was introduced. This permits detailed - analysis of the symbols used by a particular package and - construction of an accurate dependency, but it requires the - package maintainer to track more information about the shared - library. A shlibs file, in contrast, only - documents the last time the library ABI changed in any way. It - only provides information about the library as a whole, not - individual symbols. When a package is built using a shared - library with only a shlibs file, the generated + a shlibs file, which provides information on the + package dependencies required to ensure the presence of + interfaces provided by this library. Any package with binaries + or libraries linking to a shared library must use these files + to determine the required dependencies when it is built. Other + packages which use a shared library (for example using + dlopen()) should compute appropriate dependencies + using these files at build time as well. +

+ +

+ The two mechanisms differ in the degree of detail that they + provide. A symbols file documents for each symbol + exported by a library the minimal version of the package any + binary using this symbol will need, which is typically the + version of the package in which the symbol was introduced. + This permits detailed analysis of the symbols used by a + particular package and construction of an accurate dependency, + but it requires the package maintainer to track more information + about the shared library. A shlibs file, in + contrast, only documents the last time the library ABI changed + in any way. It only provides information about the library as a + whole, not individual symbols. When a package is built using a + shared library with only a shlibs file, the generated dependency will require a version of the shared library equal to or newer than the version of the last ABI change. This generates unnecessarily restrictive dependencies compared @@ -6009,7 +6014,11 @@ Built-Using: grub2 (= 1.99-9), loadlin (= 1.6e-1)

shlibs files also have a flawed representation of library SONAMEs, making it difficult to use shlibs - files in some unusual corner cases. + files in some unusual corner cases. + libfooN.shlibs says 'libfoo N' instead of the actual SONAME, + so if the SONAME doesn't match one of the two expected + formats (libfoo-N.so or libfoo.so.N) it can't be represented. +

@@ -6019,9 +6028,9 @@ Built-Using: grub2 (= 1.99-9), loadlin (= 1.6e-1) required by symbols files is not too difficult to maintain. However, maintaining exhaustive symbols information for a C++ library can be quite onerous, so shlibs - files may be more appropriate for most C++ libraries. udebs - must also use shlibs, since the udeb infrastructure - does not use symbols. + files may be more appropriate for most C++ libraries. Libraries + with a corresponding udeb must also provide shlibs, + since the udeb infrastructure does not use symbols.

@@ -6080,8 +6089,8 @@ Built-Using: grub2 (= 1.99-9), loadlin (= 1.6e-1) 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 + compiled libraries or binaries, for example using the + -T option to the dpkg utilities to specify a different substvars file for each binary package. Again, dh_shlibdeps @@ -6109,8 +6118,8 @@ Built-Using: grub2 (= 1.99-9), loadlin (= 1.6e-1) 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 the libraries used + libraries it directly uses, but not the libraries it only uses + indirectly. The dependencies for the libraries used directly will automatically pull in the indirectly-used libraries. dpkg-shlibdeps will handle this logic automatically, but package maintainers need to be aware of @@ -6154,14 +6163,15 @@ Built-Using: grub2 (= 1.99-9), loadlin (= 1.6e-1)

There are two types of ABI changes: ones that are backward-compatible and ones that are not. An ABI change is - backward-compatible if any binary was linked with the previous - version of the shared library will still work correctly with - the new version of the shared library. Adding new symbols to - the shared library is a backward-compatible change. Removing - symbols from the shared library is not. Changing the behavior - of a symbol may or may not be backward-compatible depending on - the change; for example, changing a function to accept a new - enum constant not previously used by the library is generally + backward-compatible if any reasonable program or library that + was linked with the previous version of the shared library + will still work correctly with the new version of the shared + library. Adding new symbols to the shared library is a + backward-compatible change. Removing symbols from the shared + library is not. Changing the behavior of a symbol may or may + not be backward-compatible depending on the change; for + example, changing a function to accept a new enum constant not + previously used by the library is generally backward-compatible, but changing the members of a struct that is passed into library functions is generally not unless the library takes special precautions to accept old versions of @@ -6262,10 +6272,10 @@ Built-Using: grub2 (= 1.99-9), loadlin (= 1.6e-1)

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 + provided by the shared library package as a control file, + 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. @@ -6482,9 +6492,9 @@ Built-Using: grub2 (= 1.99-9), loadlin (= 1.6e-1) 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 + dependency on zlib1g (>= 1:1.1.4), but packages using compressBound would get a dependency - of zlib1g (>= 1:1.2.0). + on zlib1g (>= 1:1.2.0).

-- 2.39.2