HP-UX Linker and Libraries User's Guide

Using HP-UX 10.X Style Initializers
The initializer is called for libraries that are loaded implicitly at program startup, or explicitly with
shl_load or dlopen. When calling initializers for implicitly loaded libraries, the dynamic loader
waits until all libraries have been loaded before calling the initializers. It calls the initializers in
depth-first order - that is, the initializers are called in the reverse order in which the libraries are
searched for symbols. All initializers are called before the main program begins execution. When
calling the initializer for explicitly loaded libraries, the dynamic loader waits until any dependent
libraries are loaded before calling the initializers. As with implicitly loaded libraries, initializers
are called in depth-first order. Note that initializers can be disabled for explicitly loaded libraries
with the BIND_NOSTART flag to shl_load. For more information, see The shl_load Summary.
This section discusses the following topics:
• “Declaring the Initializer with the +I Option” (page 143)
• “Order of Execution of Multiple Initializers” (page 143)
• “Initializer Syntax” (page 144)
• “Example: An Initializer for Each Library” (page 144)
• “Example: A Common Initializer for Multiple Libraries” (page 146)
Declaring the Initializer with the +I Option
To declare the name of the initializer, use the +I linker option when creating the shared library.
The syntax of the +I option is:
+I initializer
where initializer is the initializer's name.
Multiple initializers may be called by repeating the +I initializer option.
For example, to create a shared library named libfoo.so that uses an initializer named init_foo,
use this linker command line:
$ ld -b -o libfoo.so libfoo.o +I init_foo
Order of Execution of Multiple Initializers
Multiple initializers are executed in the same order that they appear on the command line; they
are unloaded in reverse order. (This applies only to the calling order within a shared library, not
across multiple shared libraries.)
NOTE: In PA-32 compatibility mode, initializers are not executed when unloading shared libraries
which were implicitly loaded because the program exits without re-entering the dynamic loader to
unload them. Initializers are called only during the explicit unloading of a shared library.
Initializers behave the same as other symbols; once they are bound they cannot be overridden
with a new symbol through the use of shl_definesym() or by loading a more visible occurrence
of the initializer symbol with the BIND_FIRST flag. What this means is that once the initializer is
executed upon a load, it is guaranteed to be the same initializer that is called on an explicit unload.
Initializer Syntax
void initializer( shl_t handle,
int loading )
Initializers for Shared Libraries 143