diff options
Diffstat (limited to 'ldso/man/ld.so.texi')
| -rw-r--r-- | ldso/man/ld.so.texi | 411 |
1 files changed, 0 insertions, 411 deletions
diff --git a/ldso/man/ld.so.texi b/ldso/man/ld.so.texi deleted file mode 100644 index 4e5fb841b..000000000 --- a/ldso/man/ld.so.texi +++ /dev/null @@ -1,411 +0,0 @@ -\input texinfo @c -*-texinfo-*- -@c %**start of header -@setfilename ld.so.info -@settitle ld.so : Dynamic-Link Library support -@c %**end of header - -@ifinfo -This file documents the dynamic-link support libraries and utilities for the -Linux OS, version 1.8.1. - -Copyright 1996 Michael Deutschmann - -This document is subject to the GNU General Public License as published by -the Free Software foundation, version 2 or later (your choice). - -Note: The software described in this document is under a different copyright -and license. - -@end ifinfo - -@titlepage -@title ld.so -@subtitle Dynamic Link library support for the Linux OS. -@author David Engel -@author Eric Youngdale -@author Peter Macdonald -@author Hongjiu Lu -@author Mitch D'Souza -@author Michael Deutschmann (this documentation) - -@page -Copyright @copyright{} 1996 Michael Deutschmann - -This document is subject to the GNU General Public License as published by -the Free Software foundation, version 2 or later (your choice). - -Note: The software described in this document is under a different copyright -and license. -@end titlepage - -@ifinfo -@node Top -@top - -The @code{ld.so} module provides dynamic linked library support in Linux. -This file documents @code{ld.so} and its companion software. - -@menu -* intro:: Introduction - -* ld.so:: The dynamic linker core program -* ldd:: A utility to print out dependencies -* ldconfig:: A utility to maintain the cache and symlinks -* libdl:: Manual dynamic linking library -@end menu - -@end ifinfo - -@node intro -@unnumbered Introduction - -The @code{ld.so} suite contains special files and utilities needed for linux -to handle @dfn{dynamic libraries}. - -Ordinary static libraries (@file{lib*.a} files) are included into executables -that use their functions. A file that only uses static libraries needs less -intelligence to load, but takes up more space. If many executables use the -same library, there can be much wastage of storage space, since multiple -copies of the library functions are scattered across the executables. -However, static libraries are easier to make. - -Dynamic libraries (@file{lib*.so*} files) are not copied into executables --- -the executable is written in such a way that it will automatically load the -libraries. In linux, the executable will first load the special library -@code{ld.so} or @code{ld-linux.so}, which contains the intelligence -to load further dynamic libraries. Since multiple files end up getting -executable data from the same file, dynamic libraries are also known as -shared libraries. - -Linux executables come in two flavors, @sc{elf} and a.out. - -a.out is the original executable format used by Linux. It has somewhat less -overhead than @sc{elf}. However creating shared libraries for a.out is -@emph{very} involved, and each a.out shared library must be explicitly -registered. - -@sc{elf} is a more recent format, which supports a much simpler method of -creating libraries. @sc{elf} libraries may also be linked manually -(@pxref{libdl}). - -Since many library authors prefer @sc{elf} and no longer release shared a.out -libraries, a.out is moribund on Linux. This version of the @code{ld.so} can -be compiled to support only @sc{elf}, or to support both formats. (The last -release of ld.so to support a.out alone was 1.8.0.) - -@node ld.so -@chapter @code{ld.so}: Dynamic linker core - -@code{ld.so} works behind the scenes to handle dynamic libraries in Linux. -Users will almost never have to deal with it directly, but in special cases -one can send instructions to it through environment variables. Also, if -something is wrong with your libraries (usually an incorrect version) ld.so -will give error messages. - -Actually @code{ld.so} is the a.out linker. The new @sc{elf} executables are -handled by a related program @code{ld-linux.so}. - -@menu -* files:: Configuration files used by the suite -* environment:: Environment settings that tweak @code{ld.so} -* errors:: Complaints @code{ld.so} might make -@end menu - -@node files -@section Configuration Files - -@table @file -@item /etc/ld.so.cache -A file created by @code{ldconfig} and used to speed linking. It's structure -is private to the suite. - -@item /etc/ld.so.conf -A simple list of directories to scan for libraries, in addition to -@file{/usr/lib} and @file{/lib}, which are hardwired. It may contain -comments started with a @samp{#}. - -@item /etc/ld.so.preload -A list of libraries to preload. This allows preloading libraries for -setuid/setgid executables securely. It may contain comments. -@end table - -@node environment -@section Environment Variables - -@table @code -@item LD_AOUT_LIBRARY_PATH -@itemx LD_LIBRARY_PATH -These variables supply a library path for finding dynamic libraries, in the -standard colon seperated format. These variables are ignored when executing -setuid/setgid programs, because otherwise they would be a security hazard. -@code{ld.so} will use @code{LD_AOUT_LIBRARY_PATH} and @code{ld-linux.so} will -use @code{LD_LIBRARY_PATH}. - -@item LD_AOUT_PRELOAD -@itemx LD_PRELOAD -These variables allow an extra library not specified in the executable to be -loaded. Generally this is only useful if you want to override a function. -These are also ignored when running setuid/setgid executables. @code{ld.so} -will use @code{LD_AOUT_PRELOAD} and @code{ld-linux.so} will use -@code{LD_PRELOAD}. - -@item LD_NOWARN -If non-empty, errors about incompatible minor revisions are suppressed. - -@item LD_KEEPDIR -If non-empty, allow executables to specify absolute library names. This -option is deprecated. -@c FIXME: -@c The following are things I noticed in the ld-linux.so source. -@c I don't really understand 'em. Could someone help me? -@c -@c @item LD_BIND_NOW -@c This option is used by the @code{ld-linux.so} only. I don't know -@c what it does. (I suspect, looking at the code, that it specifies -@c "RTLD_NOW" rather than "RTLD_LAZY" mode for the shared libraries.) -@c -@c @item LD_TRACE_LOADED_OBJECTS -@c @itemx LD_WARN -@c These seem to have something to do with the communication between the -@c @code{ld-linux.so} and @code{ldd}. I don't know more. -@end table - -@node errors -@section Errors - -@table @samp -@item Can't find library @var{library} -The executable required a dynamically linked library that ld.so cannot find. -Your symbolic links may be not set right, or you may have not installed a -library needed by the program. - -@item Can't load library @var{library} -The library is corrupt. - -@item Incompatible library @var{library} -@itemx Require major version @var{x} and found @var{y} -Your version of the library is incompatible with the executable. Recompiling -the executable, or upgrading the library will fix the problem. - -@item using incompatible library @var{library} -@itemx Desire minor version >= @var{x} and found @var{y}. -Your version of the library is older than that expected by the executable, -but not so old that the library interface has radically changed, so the -linker will attempt to run anyway. There is a chance that it will work, but -you should upgrade the library or recompile the software. The environment -variable @code{LD_NOWARN} can be used to supress this message. - -@item too many directories in library path -The linker only supports up to 32 library directories. You have too many. - -@item dynamic linker error in @var{blah} -The linker is having trouble handling a binary - it is probably corrupt. - -@item can't map cache file @var{cache-file} -@itemx cache file @var{cache-file} @var{blah} -The linker cache file (generally @file{/etc/ld.so.cache}) is corrupt or -non-existent. These errors can be ignored, and can be prevented by -regenerating the cache file with @code{ldconfig}. -@end table - -@node ldd -@chapter @code{ldd}: Dependency scanner - -@code{ldd} is a utility that prints out the dynamic libraries that an -executable is linked to. - -Actually @code{ldd} works by signalling ld.so to print the dependencies. -For a.out executables this is done by starting the executable with -@code{argc} equal to 0. The linker detects this and prints the dependencies. -(This can cause problems with @emph{very} old binaries, which would run as -normal only with an inappropriate @code{argc}.) - -For @sc{elf} executables, special environment variables are used to tell the -linker to print the dependencies. - -@code{ldd} has a few options: - -@table @samp -@item -v -Print the version number of @code{ldd} itself - -@item -V -Print the version number of the dynamic linker - -@item -d -Report missing functions. This is only supported for @sc{elf} executables. - -@item -r -Report missing objects. This is also only available for @sc{elf} -executables. -@end table - -@node ldconfig -@chapter @code{ldconfig}: Setup program - -This utility is used by the system administrator to automatically set up -symbolic links needed by the libraries, and also to set up the cache file. - -@code{ldconfig} is run after new dynamic libraries are installed, and if the -cache file or links are damaged. It is also run when upgrading the -@code{ld.so} suite itself. - -The @file{/lib} and @file{/usr/lib} directories, and any listed in the file -@file{/etc/ld.so.conf} are scanned by default unless @samp{-n} is used. -Additional directories may be specified on the command line. - -It has the following options: - -@table @samp -@item -D -Enter debug mode. Implies @samp{-N} and @samp{-X}. - -@item -v -Verbose. Print out links created and directories scanned. - -@item -n -Check directories specified on the commandline @emph{only}. - -@item -N -Do not regenerate the cache. - -@item -X -Do not rebuild symbolic links. - -@item -l -Set up symbolic links for only libraries presented on the command line. - -@item -p -Print out the library pathnames in the cache file (@file{/etc/ld.so.cache}) -@end table - -@node libdl -@chapter User dynamic linking library - -The @code{ld.so} package includes a small library of functions -(@code{libdl}) to allow manual dynamic linking. Normally programs are linked -so that dynamic functions and objects are automagically available. These -functions allow one to manually load and access a symbol from a library. -They are only available for @sc{elf} executables. - -@menu -* using libdl:: General points -* functions:: How to use the functions -* example:: A sample program -@end menu - -@node using libdl -@section Overview - -To access this library, add the flag @samp{-ldl} to your compile command when -linking the executable. You also must include the header file -@code{dlfcn.h}. You may also need the flag @samp{-rdynamic}, which enables -resolving references in the loaded libraries against your executable. - -Generally, you will first use @code{dlopen} to open a library. Then you use -@code{dlsym} one or more times to access symbols. Finally you use -@code{dlclose} to close the library. - -These facilities are most useful for language interpreters that provide -access to external libraries. Without @code{libdl}, it would be neccessary -to link the interpreter executable with any and all external libraries -needed by the programs it runs. With @code{libdl}, the interpreter only -needs to be linked with the libraries it uses itself, and can dynamically -load in additional ones if programs need it. - -@node functions -@section Functions - -@deftypefun void *dlopen ( const char @var{filename}, int @var{flags} ) - -This function opens the dynamic library specified by @var{filename} -and returns an abstract handle, which can be used in subsequent calls to -@code{dlsym}. The function will respect the @code{LD_ELF_LIBRARY_PATH} and -@code{LD_LIBRARY_PATH} environment variables. - -@end deftypefun - -The following flags can be used with @code{dlopen}: - -@deftypevr Macro int RTLD_LAZY -Resolve symbols in the library as they are needed. -@end deftypevr - -@deftypevr Macro int RTLD_NOW -Resolve all symbols in the library before returning, and fail if not all can -be resolved. This is mutually exclusive with @code{RTLD_LAZY}. -@end deftypevr - -@deftypevr Macro int RTLD_GLOBAL -Make symbols in this library available for resolving symbols in other -libraries loaded with @code{dlopen}. -@end deftypevr - -@deftypefun int dlclose ( void *@var{handle} ) - -This function releases a library handle. - -Note that if a library opened twice, the handle will be the same. However, -a reference count is used, so you should still close the library as many -times as you open it. - -@end deftypefun - -@deftypefun void *dlsym (void *@var{handle},char *@var{symbol-name}) - -This function looks up the name @var{symbol-name} in the library and returns -it in the void pointer. - -If there is an error, a null pointer will be returned. However, it is -possible for a valid name in the library to have a null value, so -@code{dlerror} should be used to check if there was an error. - -@end deftypefun - -@deftypefun {libdl function} {const char} *dlerror( void ) - -This function is used to read the error state. It returns a human-readable -string describing the last error, or null, meaning no error. - -The function resets the error value each time it is called, so the result -should be copied into a variable. If the function is called more than once -after an error, the second and subsequent calls will return null. - -@end deftypefun - -@node example -@section Example program - -Here is an example program that prints the cosine of two by manually linking -to the math library: - -@example -@c The following was snarfed verbatim from the dlopen.3 man file. -#include <stdio.h> -#include <dlfcn.h> - -int main(int argc, char **argv) @{ - void *handle; - double (*cosine)(double); - char *error; - - handle = dlopen ("/lib/libm.so", RTLD_LAZY); - if (!handle) @{ - fputs (dlerror(), stderr); - exit(1); - @} - - cosine = dlsym(handle, "cos"); - if ((error = dlerror()) != NULL) @{ - fputs(error, stderr); - exit(1); - @} - - printf ("%f\\n", (*cosine)(2.0)); - dlclose(handle); -@} -@end example - -@contents - -@bye |