From: Jonathan Nieder
Date: Sun, 12 Aug 2012 20:43:50 +0000 (-0700)
Subject: Clarifications to symbols and shlibs policy
X-Git-Url: https://git.donarmstrong.com/?a=commitdiff_plain;ds=sidebyside;h=b19fb874de1a4913125c5be18b244e596cf7e847;p=debian%2Fdebian-policy.git
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".
---
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).