http://www.sgi.com/tech/relnotes/6_0rel/c_eoe.html (Silicon Surf Promotional CD, 01/1995)
c_eoe Release Notes
c_eoe Release Notes
1 Introduction
A Dynamic Shared Objects
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6.0 ANSI C Execution Environment Release Notes
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1. Introduction
These notes describe the C Compiler Execution
Environment (c_eoe), version 6.0, from Silicon
Graphics, Inc. The C Compiler EOE contains C
compiler libraries supplied as DSOs (dynamic
shared objects). They support both the 32-bit
and 64-bit MIPSpro compilations modes. DSOs are
discussed in Appendix A and in the dso(5) man
page.
Note: Packaged with this software is a separate
sheet that contains the Software License
Agreement. This software is provided to
you solely under the terms and conditions
of the Software License Agreement.
Please take a few moments to review the
Agreement.
1.1 C_Applications_Prerequisite
If you plan to run any C applications, it is
important to note that you must install the C
Compiler EOE.
1.2 Release_Identification_Information
Following is the release identification
information for the C Compiler Execution
Environment (c_eoe):
Software Product ANSI C EOE
Version 6.0
System Software Requirements IRIX 6.0
1.3 6.0 C Compiler Execution Environment
Subsystems
The 6.0 C Compiler EOE software (c_eoe) includes
these subsystems:
c_eoe Standard C execution
environment
c_eoe.sw Standard C execution
software
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c_eoe.sw.lib Standard C execution
libraries
1.4 Online_Release_Notes
After you install the online documentation for a
product (the relnotes subsystem), you can view
the release notes on your screen.
If you have a graphics system, select ``Release
Notes'' from the Tools submenu of the Toolchest.
This displays the grelnotes(1) graphical browser
for the online release notes.
Refer to the grelnotes(1) man page for
information on options to this command.
If you have a nongraphics system, you can use
the relnotes command. Refer to the relnotes(1)
man page for accessing the online release notes.
1.5 Product_Support
Silicon Graphics, Inc., provides a comprehensive
product support maintenance program for its
products.
If you are in the U.S. or Canada and would like
support for your Silicon Graphics-supported
products, contact the Technical Assistance
Center at 1-800-800-4SGI. If you are outside
these areas, contact the Silicon Graphics
subsidiary or authorized distributor in your
country.
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3.18 ANSI C Execution Environment Release Notes
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Document Number 007-1659-xxx
1. Dynamic_Shared_Objects
A Dynamic Shared Object, or DSO, is an ELF
format object file, very similar in structure to
an executable program but with no "main". It
has a shared component, consisting of shared
text and read-only data; a private component,
consisting of data and the GOT (Global Offset
Table); several sections that hold information
necessary to load and link the object; and a
liblist, the list of other shared objects
referenced by this object. Most of the libraries
supplied by SGI are available as dynamic shared
objects.
A DSO is relocatable at runtime; it can be
loaded at any virtual address. A consequence of
this is that all references to external symbols
must be resolved at runtime. References from
the private region (.e.g. from private data) are
resolved once at load-time; references from the
shared region (e.g. from shared text) must go
through an indirection table (GOT) and hence
have a small performance penalty associated with
them.
Code compiled for use in a shared object is
referred to as Position Independent Code (PIC),
whereas non-PIC is usually referred to as non-
shared. Non-shared code and PIC cannot be mixed
in the same object.
At Runtime, exec loads the main program and then
loads rld, the runtime linking loader, which
finishes the exec operation. Starting with
main's liblist, rld loads each shared object on
the list, reads that object's liblist, and
repeats the operation until all shared objects
have been loaded. Next, rld allocates common
and fixes up symbolic references in each loaded
object. (This is necessary because we don't
know until runtime where the object will be
loaded.) Next, each object's init code is
executed. Finally, control is transferred to
"__start".
For a more complete discussion of DSOs,
including answers to questions frequently asked
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about them, see the dso(5) man page.