Solaris Application Programming, 1/e - Chapter 4 - Parent Directory

4.5 INFORMATION ABOUT APPLICATIONS 85
Example 4.51 The -r Option for ldd
$ ldd -r someapp
libdl.so.1 => /usr/lib/libdl.so.1
libnsl.so.1 => /usr/lib/libnsl.so.1
libgen.so.1 => /usr/lib/libgen.so.1
libm.so.1 => /usr/lib/libm.so.1
libc.so.1 => /usr/lib/libc.so.1
libsocket.so.1 => /usr/lib/libsocket.so.1
libsunmath.so.1 => (file not found)
libelf.so.1 => /usr/lib/libelf.so.1
libmp.so.2 => /usr/lib/libmp.so.2
/usr/platform/SUNW,Sun-Blade-1000/lib/libc_psr.so.1
symbol not found: sqrtf
(someapp)
symbol not found: sqrtl
(someapp)
The paths where libraries are located are hard-coded into the application at link
time. I will cover the procedure for doing this in more detail in Section 7.2.6 of
Chapter 7. At runtime, it is possible to use the LD_LIBRARY_PATH environment
variable to override where the application finds libraries, or to assist the application
in locating a particular library. So, for the case in Example 4.51, if the LD_
LIBRARY_PATH variable were set to point to a directory containing libsunmath.so,
ldd would report that the application used that version of the library.
Example 4.52 shows an example of setting the LD_LIBRARY_PATH environment
variable under csh. Of course, you can use the same environment variable to
change where the application loads all its libraries from, so be careful when setting
it and do not rely on it as the default mechanism to enable an application
locating its libraries at deployment.
Example 4.52 Example of Setting the LD_LIBRARY_PATH Variable
$ setenv LD_LIBRARY_PATH /export/home/my_libraries/
The LD_LIBRARY_PATH environment variable will override the search path for
both 32-bit and 64-bit applications. To explicitly set search paths for these two
application types you can use the environment variables LD_LIBRARY_PATH_32
and LD_LIBRARY_PATH_64.
It is also possible to set the LD_PRELOAD environment variable to specify a
library that is to be loaded before the application. This enables the use of a different
library in addition to the one shipped with the application. This can be a useful
way to debug the application’s interactions with libraries. I will cover this in
more detail in Section 7.2.10 of Chapter 7.