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