@c Copyright (C) 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2000, 2001 Free Software Foundation, Inc. @c This is part of the GCC manual. @c For copying conditions, see the file gcc.texi. @node Collect2 @chapter @code{collect2} GCC uses a utility called @code{collect2} on nearly all systems to arrange to call various initialization functions at start time. The program @code{collect2} works by linking the program once and looking through the linker output file for symbols with particular names indicating they are constructor functions. If it finds any, it creates a new temporary @samp{.c} file containing a table of them, compiles it, and links the program a second time including that file. @findex __main @cindex constructors, automatic calls The actual calls to the constructors are carried out by a subroutine called @code{__main}, which is called (automatically) at the beginning of the body of @code{main} (provided @code{main} was compiled with GNU CC)@. Calling @code{__main} is necessary, even when compiling C code, to allow linking C and C++ object code together. (If you use @option{-nostdlib}, you get an unresolved reference to @code{__main}, since it's defined in the standard GCC library. Include @option{-lgcc} at the end of your compiler command line to resolve this reference.) The program @code{collect2} is installed as @code{ld} in the directory where the passes of the compiler are installed. When @code{collect2} needs to find the @emph{real} @code{ld}, it tries the following file names: @itemize @bullet @item @file{real-ld} in the directories listed in the compiler's search directories. @item @file{real-ld} in the directories listed in the environment variable @code{PATH}. @item The file specified in the @code{REAL_LD_FILE_NAME} configuration macro, if specified. @item @file{ld} in the compiler's search directories, except that @code{collect2} will not execute itself recursively. @item @file{ld} in @code{PATH}. @end itemize ``The compiler's search directories'' means all the directories where @command{gcc} searches for passes of the compiler. This includes directories that you specify with @option{-B}. Cross-compilers search a little differently: @itemize @bullet @item @file{real-ld} in the compiler's search directories. @item @file{@var{target}-real-ld} in @code{PATH}. @item The file specified in the @code{REAL_LD_FILE_NAME} configuration macro, if specified. @item @file{ld} in the compiler's search directories. @item @file{@var{target}-ld} in @code{PATH}. @end itemize @code{collect2} explicitly avoids running @code{ld} using the file name under which @code{collect2} itself was invoked. In fact, it remembers up a list of such names---in case one copy of @code{collect2} finds another copy (or version) of @code{collect2} installed as @code{ld} in a second place in the search path. @code{collect2} searches for the utilities @code{nm} and @code{strip} using the same algorithm as above for @code{ld}.