Relocatable Code

Depends on	Memory

Another name for this, which is quite descriptive, is position independent code. A routine is relocatable if it can execute at any address. That means it cannot contain ‘absolute’ (fixed) addresses.

Most modern processors can do this quite easily (although there may need to be some option ‘flags’ set when code is compiled). Basically, addresses are specified in a relative way: for example, ‘loop back 21 lines’ rather than ‘loop back to line number 1234’*.

This is important:

in ‘primitive’ operating systems without memory mapping where code may be loaded at different places
for shared libraries where one copy of the code may appear at different virtual addresses (in different processes).

* Okay, it would be ‘addresses’ or ‘instructions’ really.

Also refer to:	Operating System Concepts, 10th Edition: Chapter 9.1.2, pages 352-353

Max. number:

Max. distance:

About this resource • Application Binary Interface (ABI) • Arrays • Atomicity • Boot • Cache • Cacheability • Caching • Concepts • Containers • Context • Context Switching • Deadlock • Direct Memory Access (DMA) • Environment Variables • Exceptions • File Attributes • Fragmentation • Hypervisor • Interrupts • Operation Ordering • PATH • Pointers • Process Scheduling • Processes • Processor Privilege • Queues • Real Time • Reentrancy • Relocatable Code • Spooling and Buffering • Synchronisation • Thrashing • Threads • Virtual Memory • Virtualisation

Articles on Memory

About this resource • Arrays • Cache • Caching • Direct Memory Access (DMA) • Dirty Bit • Dynamic Memory Allocation • Memory • Memory Barrier • Memory Fault • Memory Leak • Memory Management • Memory Management Unit (MMU) • Memory Mapped Files • Memory Mapping • Memory Mapping Example • Memory Mapping Extra • Memory Pages • Memory Protection • Memory Segmentation • Memory Sizes • Monitoring page behaviour • Page Eviction • Paging • Paging States • Pointer Arithmetic • Pointers • Relocatable Code • Resources • Shared Memory • Structures • Translation Look-aside Buffer (TLB) • Virtual Memory • Write Buffer

Articles on User

"Everything is a File" • Application Binary Interface (ABI) • Arrays • Boot • Buffer Overflow • Containers • Daemons • Disk Partition • Dynamic Memory Allocation • Emulator traps • Environment Variables • Errors • Exceptions • File Attributes • File Locking • File Permissions • Introduction to Operating Systems • Journalling File System • Links • Locks • Man(ual pages in Unix) • Memory Mapped Files • Monitoring • Network File System (NFS) • PATH • Pipes • Pointers • Relocatable Code • Reset • SETUID • Shell • Sockets • Spooling and Buffering • Streams • Structures • Superuser • System Calls • Unix Signals • User • Using Peripherals

Relocatable Code

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