dyld - the dynamic link editor

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SYNOPSIS

DESCRIPTION

DYLD_LIBRARY_PATH

This is set to a colon separated list of directories to change which libraries a program uses. Then for each library install name recorded in the executable, bundles and dependent libraries the program uses, the last component of the install name is appended with each of the directories in DYLD_LIBRARY_PATH in turn. The first file that is found is then used for the library. If none is found then the install name as recorded is used. This allows such things as testing new versions of existing dynamic shared libraries. The recorded library install name can be seen with the -L option to otool.1

DYLD_INSERT_LIBRARIES

This is set to a colon separated list of dynamic library filenames to add additional libraries to a program when run. The libraries listed in the list are loaded before the libraries recorded in the executable, bundles and dependent libraries. This allows such things as testing new modules of existing dynamic shared libraries by creating a temporary dynamic shared library with just the new modules.

DYLD_PRINT_LIBRARIES

When this is set the dynamic link editor writes to file descriptor 2 (normally standard error) the filenames of the libraries the program is using. This is useful to make sure that the use of DYLD_LIBRARY_PATH is getting what you want.

DYLD_MEM_PROTECT

When this is set it causes the dynamic link editor to change the protection of the memory it uses for its data structures when it is not operating on them. It is possible for an errant program to mistakenly write on the data structures of dynamic link editor. This is used to help track down the point the program does it's mistaken write. This will then cause the program to crash at the first occurrence of a write making the error easier to track down. Unfortunately this can't be done in the debugger as the debugger's interface to the dynamic link editor will cause the dynamic link editor's memory to remain writable. But can produce a very useful core file.

DYLD_EBADEXEC_ONLY

When this is set it causes the dynamic link editor to do all of the work needed to launch the program without launching it. This will either print the cause why the program could not be launch or print a message saying the program could be launched. This can be used a supplement to the program ebadexec.1 to determine why a program can't be launched. For programs that should not have any undefined symbols when launched the DYLD_BIND_AT_LAUNCH can also be set to check this (see below).

DYLD_BIND_AT_LAUNCH

When this is set it causes the dynamic link editor to bind all undefined symbols the program needs at launch time. This includes function symbols that can are normally lazily bound at the time of their first call.

DYLD_DEAD_LOCK_HANG

When this is set it causes the dynamic link editor to enter a loop that hangs the program if a thread doing a dynamic link editor operation attempts to start another dynamic link editor operation before completing the first. This allows a debugger to be attached to such processes instead of letting this error to cause the program to exit so the problem can be fixed.

DYLD_PREBIND_DEBUG

When set it causes the dynamic link editor to print diagnostics as to the launching of programs and libraries build prebound. This allows determining why a program is not being launch prebound. The recorded library time stamps can be seen with the -Lv option to otool.1

For secure programs that are UNIX set uid or set gid, the searching of libraries with the environment variable and the insertion of libraries will not be done, unless the program is run as the real user. For secure programs the dynamic link editor clears out the value of DYLD_LIBRARY_PATH. This is so that if a program is exec.2 from a secure program it too will not have it's libraries searched for. For staticly linked secure programs that exec.2 other programs that might being using the dynamic link editor they too should clear out the value of DYLD_LIBRARY_PATH.

SEE ALSO

Created by unroff & hp-tools. © somebody (See intro for details). All Rights Reserved. Last modified 11/5/97