ld-elf.so.2 man page on DragonFly

Man page or keyword search:  
man Server   44335 pages
apropos Keyword Search (all sections)
Output format
DragonFly logo
[printable version]

RTLD(1)			  BSD General Commands Manual		       RTLD(1)

NAME
     ld-elf.so.1, ld-elf.so.2, rtld, _rtld_functrace — run-time link-editor

SYNOPSIS
     int
     _rtld_functrace(const char *callerso, const char *calleeso,
	 const char *calleefun, void *stack);

DESCRIPTION
     ld-elf.so.1 is a self-contained shared object providing run-time support
     for loading and link-editing shared objects into a process' address
     space.  It is also commonly known as the dynamic linker.  It uses the
     data structures contained within dynamically linked programs to determine
     which shared libraries are needed and loads them using the mmap(2) system
     call.

     After all shared libraries have been successfully loaded, ld-elf.so.1
     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.  This is useful for C++ libraries that contain static construc‐
     tors.

     ld-elf.so.1 itself is loaded by the kernel together with any dynamically-
     linked program that is to be executed.  The kernel transfers control to
     the dynamic linker.  After the dynamic linker has finished loading, relo‐
     cating, and initializing the program and its required shared objects, it
     transfers control to the entry point of the program.

     To locate the required shared objects in the filesystem, ld-elf.so.1 may
     use a “hints” file prepared by the ldconfig(8) utility.

     ld-elf.so.1 recognizes 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 is
		      ignored for set-user-ID and set-group-ID programs.

     LD_PRELOAD	      A list of shared libraries, separated by colons and/or
		      white space, to be linked in before any other shared
		      libraries.  If the directory is not specified then the
		      directories specified by LD_LIBRARY_PATH will be
		      searched first followed by the set of built-in standard
		      directories.  This is ignored for set-user-ID and set-
		      group-ID programs.

     LD_BIND_NOW      When set to a nonempty string, causes ld-elf.so.1 to
		      relocate all external function calls before starting
		      execution of the program.	 Normally, function calls are
		      bound lazily, at the first call of each function.
		      LD_BIND_NOW increases the start-up time of a program,
		      but it avoids run-time surprises caused by unexpectedly
		      undefined functions.

     LD_TRACE_LOADED_OBJECTS
		      When set to a nonempty string, causes ld-elf.so.1 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 conveniently.  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

		      %o    The library name.

		      %m    The library's major version number.

		      %p    The full pathname as determined by rtld's library
			    search rules.

		      %x    The library's load address.

		      Additionally, ‘\n’ and ‘\t’ are recognized and have
		      their usual meaning.

     If a shared object preloaded by the LD_PRELOAD mechanism contains a pub‐
     lic symbol “_rtld_functrace”, ld-elf.so.1 will transfer control to this
     function each time it needs to resolve an unbound function symbol.	 By
     returning a non-zero value, _rtld_functrace() can advise the linker to
     keep tracing the specified combination of caller shared object and called
     function; returning 0 will prevent _rtld_functrace() to be called for
     this combination again.

     When implementing a custom _rtld_functrace() function, be aware of the
     possibility that _rtld_functrace() might be called for functions called
     on its behalf, or that multiple threads could enter _rtld_functrace() at
     the same time.

DIFFERENCES BETWEEN .1 and .2
     ABI changes have been made to support TLS allocation and initialization
     and to give threading libraries a chance to complete initialization of
     the TCB prior to the calling of the _init() functions for the dynamically
     loaded libraries.

FILES
     /var/run/ld-elf.so.hints

EXAMPLES
     To set up an _rtld_functrace() for printing out the functions as they are
     called, this code can be used:

	   #include <string.h>

	   static int nl = 10;

	   int
	   _rtld_functrace(const char *callerso, const char *calleeso,
	       const char *calleefun, void *stack)
	   {
		   write(2, "calling ", 8);
		   write(2, calleefun, strlen(calleefun));
		   write(2, &nl, 1);
		   return 1;
	   }

     If put in a file named ft.c and compiled with

	   $ cc -shared ft.c -o ft.so

     setting LD_PRELOAD to the path of ft.so will activate it.

SEE ALSO
     ld(1), ldd(1), elf(5), ldconfig(8)

BSD			       February 21, 2011			   BSD
[top]

List of man pages available for DragonFly

Copyright (c) for man pages and the logo by the respective OS vendor.

For those who want to learn more, the polarhome community provides shell access and support.

[legal] [privacy] [GNU] [policy] [cookies] [netiquette] [sponsors] [FAQ]
Tweet
Polarhome, production since 1999.
Member of Polarhome portal.
Based on Fawad Halim's script.
....................................................................
Vote for polarhome
Free Shell Accounts :: the biggest list on the net