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@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

a hard coded linker file name, if GCC was configured with the

@option{--with-ld} option.

@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}.