<Li> Known on the Windows platform as "DLL Hell", an incompatible updated library will break executables that depended on the behavior of the previous version of the library if the newer version is incorrectly not backward compatible . </Li> <Li> A program, together with the libraries it uses, might be certified (e.g. as to correctness, documentation requirements, or performance) as a package, but not if components can be replaced . (This also argues against automatic OS updates in critical systems; in both cases, the OS and libraries form part of a qualified environment .) </Li> <P> Static linking is the result of the linker copying all library routines used in the program into the executable image . This may require more disk space and memory than dynamic linking, but is more portable, since it does not require the presence of the library on the system where it runs . Static linking also prevents "DLL Hell", since each program includes exactly the versions of library routines that it requires, with no conflict with other programs . A program using just a few routines from a library does not require the entire library to be installed . </P> <P> As the compiler has no information on the layout of objects in the final output, it cannot take advantage of shorter or more efficient instructions that place a requirement on the address of another object . For example, a jump instruction can reference an absolute address or an offset from the current location, and the offset could be expressed with different lengths depending on the distance to the target . By generating the most conservative instruction (usually the largest relative or absolute variant, depending on platform) and adding relaxation hints, it is possible to substitute shorter or more efficient instructions during the final link . This step can be performed only after all input objects have been read and assigned temporary addresses; the linker relaxation pass subsequently reassigns addresses, which may in turn allow more relaxations to occur . In general, the substituted sequences are shorter, which allows this process to always converge on the best solution given a fixed order of objects; if this is not the case, relaxations can conflict, and the linker needs to weigh the advantages of either option . </P>

What is linker and loader in system programming