Dynamic loading

Question

Does Dynamic loading require special support from the operating system.

Comments

@Reena

Question was " Does Dynamic loading require special support from the operating system. "

So, I think it needs support from OS, otherwise how memory space could be utilized?

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From Galvin (Section 8.1.4) of 7^th edition:

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do you know why it requires special support from OS (i am talking about linking(dynamic))

Answer 1

Dynamic Loading and overlays does not require any special support from the operating system.they can be implemented completely by the user.

Dynamic Linking generally requires Hardware support

Comments

but sir, then why we say that we don't need any kind of OS support in dynamic loading unlike Dynamic linking?

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I think, In Dynamic linking, there might be a lot of protection concerns, in the sense when in the main memory lot of process are running in the main memory than in order to prevent and not modify the data from one process to another, our OS has to do lot of work like we know with limit register and base register. and by this, we can restrict the process to access the data between these two registers.In dynamic link libraries, sometimes a process might ask to access the data which is present in the space(memory) of another process.in these cases, our OS has to be careful.Therefore it requires OS support

Dynamic loading does not require special support from Operating system, it is the responsibility of the programmer to check whether the routine that is to be loaded does not exist in main memory.

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I honestly believe questions like these which depend a lot on implementation should not be asked.

Following lines are from wikipedia dynamic loading page.

Operating system that handle dynamic loading transparently

Dynamic loading was a common technique for IBM's operating systems for System/360 such as OS/360, particularly for I/O subroutines, and for COBOL and PL/I runtime libraries, and continues to be used in IBM's operating systems for z/Architecture, such as z/OS. As far as the application programmer is concerned, the loading is largely transparent, since it is mostly handled by the operating system (or its I/O subsystem). 

Operating systems that do not provide out of box support for dynamic loading, but provides libraries for developer to handle it in their code:

Not all systems support dynamic loading. UNIX-like operating systems such as macOS, Linux, and Solaris provide dynamic loading with the C programming language "dl" library. The Windows operating system provides dynamic loading through the Windows API. 

What you think guys should such questions be asked? Or its that since Unix and Windows today form most part of OS used we should not consider others. But then I bet there must be other questions which can have different answers on Unix and Windows.

Answer 2

I have read some articles on dynamic linking and shared library. And as far as i have understood the concept 'Dynamic loading requires support from kernel. The process goes like following:

prog invoked on bash-> bash forks itself and replaces its address space with the program to run ->The kernel verifies whether the required library resides in the memory. If not, it will load the file into memory and does the relocation of library symbols-> It then invokes the dynamic linker to resolve unresolved symbols of the program (referring to stub) ->Then the control transfers to our program main

If I am wrong please do share your knowledge.