eld Manual

eld Manual—527255-009
3-1
3 Binding of References
This section contains the following topics:
•
Overview -an overview of symbol resolution and code relocation.
•
Presetting Loadfiles - the process of resolving references to DLLs at linktime.
•
To Preset or Not to Preset, and Creation of the LIC - the linker’s rules for
presetting.
•
Handling Unresolved References - what happens if a symbol is not found in any
loadfile in the linker’s search list?
•
Using User Libraries - introduces the libname options.
•
Creating Import Libraries - three types are available.
•
Ignoring Optional Libraries - a command stream toggle is available.
•
Merging Symbols Found in Input Linkfiles - merges the symbol information from
the input files into its output file.
•
Accepting Multiply-Defined Symbols - how to accept multiple definitions for a
symbol?
•
Using the -cross_dll_cleanup option - reduces the total size of a program and the
private DLLs that are used by a process.
•
Specifying Which Symbols to Export, and Creating the Export Digest - to export
global and defined symbols.
•
Public Libraries and DLLs - two types, namely implicit and explicit.
•
The Public Library Registry - lists all public DLLs by name.
•
Finding and Reading The Public DLL Registry (ZREG) File - how the linker finds
the file.
Overview
The primary job of the linker is to bind abstract (symbolic) names to real addresses.
For example, as a programmer you can use the name getfile in one module, while
the linker binds that to “a location 512 bytes from the start of module iosys”. This is
known as symbol resolution.
The other closely related function of
eld is that of relocation. Compilers and
assemblers generally create each file of object code with the program address starting
at zero, an address you are unlikely to be able to use. Furthermore if a program is
created from multiple subprograms, all the subprograms have to be loaded at non-
overlapping addresses. These addressing problems are solved by relocation, the
process of assigning load addresses to the various parts of the program, adjusting the
code and data in the program to reflect the assigned addresses.