LD.SO(1) BSD Reference Manual LD.SO(1)
ld.so - run-time link-editor
ld.so is a self-contained, position independent program image providing run-time support for loading and link-editing shared objects into a process's address space. It uses the data structures (see link(5)) con- tained within dynamically linked programs to determine which shared li- braries are needed and loads them at a convenient virtual address using the mmap(2) system call. After all shared libraries have been successfully loaded, ld.so proceeds to resolve external references from both the main program and all objects loaded. A mechanism is provided for initialization routines to be called, on a per-object basis, giving a shared object an opportunity to perform any extra set-up, before execution of the program proper begins. ld.so is itself a shared object that is initially loaded by the kernel. To quickly locate the required shared objects in the filesystem, ld.so may use a "hints" file, prepared by the ldconfig(8) utility, in which the full path specification of the shared objects can be looked up by hashing on the 3-tuple <library-name, major-version-number, minor-version- number>. ld.so recognises a number of environment variables that can be used to modify its behaviour as follows: LD_LIBRARY_PATH A colon separated list of directories, overriding the default search path for shared libraries. This variable is ignored for set-user-ID and set-group-ID executables. LD_PRELOAD A colon separate list of library names to load before any of the regular libraries are loaded. This variable is ignored for set- user-ID and set-group-ID executables. LD_BIND_NOW Specifies that the dynamic linker should process all relocations before transferring control to the program. Normally, the pro- cedure linkage table entries are handled lazily, avoiding symbol lookup and relocation for unused functions. This variable is ig- nored for set-user-ID and set-group-ID executables. LD_WARN_NON_PURE_CODE When set, issue a warning whenever a link-editing operation re- quires modification of the text segment of some loaded object. This is usually indicative of an incorrectly built library. <not yet supported> LD_SUPPRESS_WARNINGS When set, no warning messages of any kind are issued. Normally, a warning is given if a satisfactorily versioned library could not be found. <not yet supported> LD_TRACE_LOADED_OBJECTS When set, causes ld.so to exit after loading the shared objects and printing a summary which includes the absolute pathnames of all objects, to standard output. LD_TRACE_LOADED_OBJECTS_FMT1 LD_TRACE_LOADED_OBJECTS_FMT2 When set, these variables are interpreted as format strings a la printf(3) to customize the trace output and are used by ldd(1)'s -f option and allows ldd(1) to be operated as a filter more con- veniently. The following conversions can be used: %a The main program's name (also known as "__progname"). %A The value of the environment variable LD_TRACE_LOADED_OBJECTS_PROGNAME. <not yet supported> %o The library name. %m The library's major version number. %n The library's minor version number. %p The full pathname as determined by ld.so's library search rules. %x The library's load address. Additionally, \n and \t are recognised and have their usual mean- ing. <not yet supported> LD_NO_INTERN_SEARCH When set, ld.so does not process any internal search paths that were recorded in the executable. <not yet supported> LD_NORANDOM When set, do not load shared objects or libraries dependent ob- jects in random order. This variable is ignored for set-user-ID and set-group-ID executables. LD_NOSTD_PATH <not yet supported> When set, do not include a set of built-in standard directory paths for searching. This might be useful when running on a system with a completely non-standard filesystem layout. LD_DEBUG When set, be verbose about what ld.so does. LD_NOPREBIND When set, ignore any prebind data associated with the program or libraries. LD_PREBINDVALIDATE When set, perform symbol relocation of the given binary and the associated libraries, compare the results against the prebind values, then exit.
/var/run/ld.so.hints library location hints built by ldconfig(8)
ld(1), link(5), ldconfig(8)
The shared library model employed first appeared in SunOS 4.0. MirOS BSD #10-current June 27, 1995 1
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