What is the difference between loading and linking

Efficent utilization of memory. Statically linked program takes constant load time every time it is loaded into the memory Dynamic linking is performed at run time by for execution. If the static loading is used then accordingly If the dynamic loading is used then accordingly static linking is applied. In dynamic linking this is not the case and Static linking is performed by programs individual shared modules can be updated and called linkers as the last step in compiling a recompiled.

This is one of the greatest program. Linkers are also called link editors. However, most programs also need to run functions from the system libraries, and these library functions also need to be loaded. Such a program is statically linked to its libraries, and statically linked executable codes can commence running as soon as they are loaded.

Disadvantage: Every program generated must contain copies of exactly the same common system library functions. In terms of both physical memory and disk-space usage, it is much more efficient to load the system libraries into memory only once. Dynamic linking allows this single loading to happen. Dynamic Linking: Every dynamically linked program contains a small, statically linked function that is called when the program starts.

This static function only maps the link library into memory and runs the code that the function contains. The link library determines what are all the dynamic libraries which the program requires along with the names of the variables and functions needed from those libraries by reading the information contained in sections of the library.

After which it maps the libraries into the middle of virtual memory and resolves the references to the symbols contained in those libraries. Advantage: Memory requirements of the program are reduced. A DLL is loaded into memory only once, whereas more than one application may use a single DLL at the moment, thus saving memory space. Position independent code runs no matter where it is located. It can employ relative rather than absolute addressing.

Although the code is located differently in each address space, locations within the library maintain the same offsets from each other. Addressing using these offsets is called relative addressing, and it is one component of PIC. Another is to collect up all absolute addresses into a table, and within the code reference the variable by its location in the table.

Then by having a separate copy of the table for each address space, the table can be filled out with the absolute addresses appropriate for the space. This occurs across most unix variants and is called the global offset table GOT.

The GOT solves the problem of shared libraries. It could be used to record the absolute addresses of both proceedures and code so that the library can refer to those locations in an position independent way. However, for functions, an additional mechanism is used, the procedure linking table PLT. This is not so much a table as a vector of jumps.

The jumps include pulling the target of the jump from the GOT. A call to one of these vectors is therefore like calling the procedure whose address is found in the GOT table.

This means they don't need to be loaded, just linked, which may be faster. Some OSs such as OSX and sometimes Linux support pre-linking, which is a process where a script runs over the applications on your system before you launch them, and does the linking.

When you launch them, you then don't need to link them. This is important because linking takes a considerable amount of your computer's time when you launch an app, and some apps may be launched multiple times a second, such as gcc , cpp and as during application build process, or filter scripts when indexing your computer's data OSX Spotlight.

Linking is the process of taking some smaller executables and joining them together as a single larger executable. Static linking occurs at compilation time, hence it occurs prior to loading a program. With static linking the external symbols that are used by your program e.

Dynamic linking occurs at run time, so it occurs after or at the time of the loading of a program. With dynamic linking the symbols are resolved either at loading time, or at run time when the symbol is accessed lazy binding. The latter is more common. Now, I have 2 libraries that is finally linked together to generate the executable like.

This process of linking information from lib1. Now, I need to load this into memory in order to run it to see the behaviour of the final executable. The process of loading the final executable like. I hope this would clear the importance of linking and loading however the definitions are not appropriate First, the libraries are loaded, along with all their dependencies and those libraries' dependencies, and so on.

Then the dynamic linker resolves symbols in the loaded libraries. Usually both of these functions are implemented by the same piece of software; on Linux it's ld. Symbols in static libraries are resolved at link time and included in the executable file itself. The stub calls into the OS. If the library is currently not loaded, it gets loaded this step is called dynamic loading.

Then, the stub is modified so that it calls the imported function directly the next time it gets called. This process is called dynamic linking. The component of the OS that performs both steps is called the dynamic linker or the dynamic linking loader.

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Learn more. Difference between dynamic loading and dynamic linking in the OS Ask Question. Asked 3 years, 5 months ago. Active 1 year, 10 months ago. Viewed 17k times. What I understood until now is this. Improve this question. Community Bot 1. So this is a total duplication of this stackoverflow.