link system

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Environment
This section describes several environment variables that affect how GCC operates. Some of them work by specifying directories or prefixes to
use when searching for various kinds of files. Some are used to specify other aspects of the compilation environment.
Note that you can also specify places to search using options such as -B, -I and -L. These take precedence over
places specified using environment variables, which in turn take precedence over those specified by the configuration of GCC .
LIBRARY_PATH
The value of LIBRARY_PATH is a colon-separated list of directories, much like PATH . When configured as a native
compiler, GCC tries the directories thus specified when searching for special linker files, if it can't find them using
GCC_EXEC_PREFIX . Linking using GCC also uses these directories when searching for ordinary libraries for the
-l option (but directories specified with -L come first).
The linker uses the following search paths to locate required shared libraries:
1.
Any directories specified by -rpath-link options.
2.
Any directories specified by -rpath options. The difference between -rpath and -rpath-link is that directories
specified by -rpath options are included in the executable and used at runtime, whereas the -rpath-link option is only
effective at link time. Searching -rpath in this way is only supported by native linkers and cross linkers which have been configured with the
--with-sysroot option.
3.
On an ELF system, if the -rpath and "rpath-link" options were not used, search the contents of the environment
variable "LD_RUN_PATH". It is for the native linker only.
4.
On SunOS, if the -rpath option was not used, search any directories specified using -L options.
5.
For a native linker, the contents of the environment variable "LD_LIBRARY_PATH".
6.
For a native ELF linker, the directories in "DT_RUNPATH" or "DT_RPATH" of a shared library are searched for shared
libraries needed by it. The "DT_RPATH" entries are ignored if "DT_RUNPATH" entries exist.
7.
The default directories, normally /lib and /usr/lib.
8.
For a native linker on an ELF system, if the file /etc/ld.so.conf exists, the list of directories found in that file.
If the required shared library is not found, the linker will issue a warning and continue with the link.
               
               
               

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