Thanks... -----Original Message----- From: fedora-list-bounces@xxxxxxxxxx [mailto:fedora-list-bounces@xxxxxxxxxx] On Behalf Of Tommy Reynolds Sent: Friday, April 30, 2004 12:53 PM To: For users of Fedora Core releases Subject: Re: Lib Version Uttered Alexander Dalloz <alexander.dalloz@xxxxxxxxxxxxxxxx>, spake thus: > Am Fr, den 30.04.2004 schrieb Tim Clarke um 17:20: > > Alex, pardon my ignorance but how does glibc-*2.3.2 work out to be > > libc6?!? > So libc.so.6 means libc6 means glibc version 6 and is packaged in the > glibc-2.3.2-101.4 RPM. Someone else may give you a more precise and > better informed answer than me. The intent of the whole setup is to allow multiple versions of shared libraries because an application gets built expecting a particular version of the library, perhaps because of ABI issues. To that end, each library includes its name builtin to the shared library itself. So when a program is linked against a library (-lfoo), the linker looks into the shared library and adds its "internal" name into the executables list of shared libraries. If you look, you will usually see a series of symbolic links pointing to the actual shared library itself: glibc.so --> glibc-6.so glibc-6.1 --> glibc-6.1.2.so It is the use of these intermediate symbolic links that makes this work. The "glibc-6.1.2.so" library indentifies itself as "glibc-6.so", by means of that "internal" name I mentioned. So when the program linker binds "glibc.so", it actually finds the library file "glibc-6.1.2.so" whose internal name is "glibc-6.so" and that's the library name placed in the executables list of necessary shared libraries. Now when the application gets executed, the system first runs a shared-program loader that ensures that all prerequisite shared libraries are in memory. The shared program loader (ld.so) looks in the executables shared library table, finds "glibc-6.so" and then links the executable to that file. When a new version of the shared library becomes available, say "glibc-6.1.3.so", all that is necessary is to install the new file and change the symbolic links: glibc.so --> glibc-6.so glibc-6.so --> glibc-6.1.3.so and when the executable program is loaded again, the ld.so looks for shared library file "glibc-6.so" and automatically gets the newer version of the library. When an interface is changed in the shared library, the new release has a different minor number (the "1" in "glibc-6.1.3.so") the new version is installed and the directory listing looks a bit like this: glibc.so --> glibc-6.so glibc-6.so --> glibc-6.2.0.so glibc-6.1.3.so glibc-6.2.0.so It's all a bit confusing but just remember there are _two_ linking times when a shared library is used: 1) when "ld" binds the shared library to the executable and; 2) when "ld.so" attaches the shared library to the executable at run time. Cheers!
