CODEWITHSUNDEEP
c++linker
Spandan
Spandan

Reputation: 33

How does a linker produce a library? What are the contents of that library?

Referring to this answer: https://stackoverflow.com/a/6264256/5324086, I found that a linker has even more functionality than just managing absolute addresses for object file symbols.

What does the library produced by linker contain? Is it something other than ... say a C Standard library?

Why does the linker even need to produce a library?

Upvotes: 0

Views: 55

Answers (2)

Matteo Italia
Matteo Italia

Reputation: 126957

Static libraries are just a collection of object files. You can think of them as a tar file containing all the relevant .a files (or, on Windows, as a zip file containing obj files). The linking part of the linker is not involved here (in facts traditionally static libraries on Unix systems are done with the ar utility, which is somehow related to tar). They are completely resolved at compile time, and they are simply used as a way to avoid rebuilding all the time stuff that is long to build or has complex build procedures.

Dynamic libraries are a different beast. They are fully fledged executables that can be loaded by other processes, so the regular linker is needed for the same reasons it is used in normal executables. Instead of providing just a single entrypoint, they export a full symbols table that is used by the loader (or "runtime linker") to allow the host program to locate the required procedures. Generally they also contain relocation information to allow loading at any address in the target address space (or they are compiled in position independent code for this same reason).

Upvotes: 0

Davislor
Davislor

Reputation: 15164

The exact details depend on the type of library (you can search for shared library formats) but the basic components will include the compiled code, plus a symbol table that tells the linker which address corresponds to each name. Note that this is very similar to an object file. Static libraries are basically archives of object files and the compiler links them in a similar way. With dynamic libraries, the OS can look this up whenever it loads a program, and link the symbols then. They won't generally have the same absolute addresses in every program's address space, so these addresses will be relative to where the OS loads the library.

The C standard library (MSVC runtime on Windows) is an example of a library.

Upvotes: 3

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