Section 6.6. Dynamic Linking and Shared Libraries

6.6. Dynamic Linking and Shared Libraries

HP-UX applications that use dynamic linking functions such as shl_load, shl_finsym, and others need to be ported to use Linux dynamic link functions that begin with dl. HP-UX applications that already use the dl* functions need to be checked for proper API use because some dl functions that HP-UX supports are not supported on Linux.

Table 6-10 shows the HP-UX dl* function equivalents to HP-UX shl_* calls as well as other dl* calls present in HP-UX only.

Table 6-10. Dynamic Loading Library Functions Comparison Table

Routines	dl* Routines Present in HP-UX and Linux	Description
shl_load and cxxshl_load	dlopen HP-UX mode: RTLD_LAZY, RTLD_NOW, RTLD_GLOBAL, RTLD_LOCAL, RTLD_GROUP, RTLD_WORLD, RTLD_PARENT Linux flags: RTLD_LAZY, RTLD_NOW, RTLD_GLOBAL, RTLD_LOCAL, RTLD_NODELETE, RTLD_NOLOAD, RTLD_BINDING_MASK, RTLD_DEEPBIND	Loads a shared library.
shl_findsym	dlsym HP-UX handle: RTLD_DEFAULT, RTLD_NEXT, RTLD_SELF Linux handle: RTLD_DEFAULT, RTLD_NEXT	Finds the address of a global symbol in a shared library.
shd_get	dlget (HP-UX only)	Gets information about currently loaded library.
shl_gethandle	dlmodinfo (HP-UX only)	Gets descriptor information about a loaded shared library.
shl_definesym	No equivalent	Adds a new symbol to the global shared library symbol table.
shl_getsymbols	No equivalent	Returns a list of symbols in a shared library.
shl_unload	dlclose	Unloads the shared library.
None	dlerror	Returns a pointer to information about the last dlopen, dlsym, or dlclose error.
None	dladdr HP-UX DI_info structure: const char *dli_fname; void *dli_fbase; const char *dli_sname; void *dli_saddr; size_t dli_size; int dli_bind; int dli_type;	Translates address to symbolic information.
	Linux DI_info structure: const char *dli_fname; void *dli_fbase; const char *dli_sname; void *dli_saddr; size_t dli_size;
	dlgetname (HP-UX only)	Retrieves the name of a loaded module given a load model descriptor.

In Linux, a program that uses dynamic linking is linked with the libld.so library, -ldl. The libraries it loads do not need to be linked in during the build process. Chapter 3 contains example code that compiles on Linux using dl* routines.

6.6.1. GNU libtool

If portability is important to your program, you should consider using GNU libtool to build and install libraries. libtool masks the complexity of using shared libraries with a consistent, portable interface. For more information, visit www.gnu.org/software/libtool/libtool.html.