User's Manual

if (shl_findsym(&lib_handle, DRAW2D, TYPE_PROCEDURE, (void *) &draw2d))
perror("shl_findsym: error finding function draw2d"), exit(1);
if (shl_findsym(&lib_handle, MAXX, TYPE_DATA, (void *) &maxX))
perror("shl_findsym: error finding data maxX"), exit(1);
if (shl_findsym(&lib_handle, MAXY, TYPE_DATA, (void *) &maxY))
perror("shl_findsym: error finding data maxY"), exit(1);
/*
* Using the routines, draw a line from (0,0) to (maxX,maxY):
*/
(*gopen)(); /* open the graphics device */
(*move2d)(0,0); /* move to pixel 0,0 */
(*draw2d)(*maxX,*maxY); /* draw line to maxX,maxY pixel */
(*gclose)(); /* close the graphics device */
}
Shown below is the compile line for this program, along with the commands to set SHLPATH
appropriately before running the program. SHLPATH is declared and used by load_lib(),
defined in “The shl_load Routine” (page 168) and cxxshl_load Routines example. Notice that
load_lib() is compiled here along with this program. Finally, this example assumes you have
created a graphics library, libgrphdd.so:
$ cc -Aa -o drawline shl_findsym.c load_lib.c -ldld
$ SHLPATH=/usr/lib/libgrphdd.so
$ export SHLPATH
$ drawline
The shl_get and shl_get_r Routines
The shl_get and shl_get_r routines obtain information on the currently loaded libraries.
Syntax
int shl_get( int index,
struct shl_descriptor **desc )
Parameters
Specifies an ordinal number of the shared library in the process. For libraries loaded implicitly
(at startup time), index is the ordinal number of the library as it appeared on the command line.
index
For example, if libc was the first library specified on the ld command line, then libc has an
index of 1. For explicitly loaded libraries, index corresponds to the order in which the libraries
were loaded, starting after the ordinal number of the last implicitly loaded library. Two index
values have special meaning:
Refers to the dynamic loader (dld.so)-1
Refers to the main program itself.-2
A shared library's index can be modified during program execution by either of the following
events:
• The program loads a shared library with the BIND_FIRST modifier to shl_load. This
increments all the shared library indexes by one.
• The program unloads a shared library with shl_unload. Any libraries following the unloaded
library have their index decremented by one.
Returns a pointer to a statically allocated buffer (struct shl_descriptor **) containing a
shared library descriptor. The structure contains these important fields:
desc
The start address (unsigned long) of the shared library text segment.tstart
The end address (unsigned long) of the shared library text segment.tend
The start address (unsigned long) of the shared library data segment.dstart
The end address (unsigned long) of the shared library bss segment. The data
and bss segments together form a contiguous memory block starting at dstart
and ending at dend.
dend
The shl_load Shared Library Management Routines 175