gccint.info: Collect2

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`collect2'

   GNU CC uses a utility called `collect2' on nearly all systems to
arrange to call various initialization functions at start time.
   The program `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 `.c' file containing a table of them, compiles it, and
links the program a second time including that file.
   The actual calls to the constructors are carried out by a subroutine
called `__main', which is called (automatically) at the beginning of
the body of `main' (provided `main' was compiled with GNU CC).  Calling
`__main' is necessary, even when compiling C code, to allow linking C
and C++ object code together.  (If you use `-nostdlib', you get an
unresolved reference to `__main', since it's defined in the standard
GCC library.  Include `-lgcc' at the end of your compiler command line
to resolve this reference.)
   The program `collect2' is installed as `ld' in the directory where
the passes of the compiler are installed.  When `collect2' needs to
find the _real_ `ld', it tries the following file names:
   * `real-ld' in the directories listed in the compiler's search
     directories.
   * `real-ld' in the directories listed in the environment variable
     `PATH'.
   * The file specified in the `REAL_LD_FILE_NAME' configuration macro,
     if specified.
   * `ld' in the compiler's search directories, except that `collect2'
     will not execute itself recursively.

* `ld' in `PATH'.

   "The compiler's search directories" means all the directories where
`gcc' searches for passes of the compiler.  This includes directories
that you specify with `-B'.
   Cross-compilers search a little differently:
   * `real-ld' in the compiler's search directories.
   * `TARGET-real-ld' in `PATH'.
   * The file specified in the `REAL_LD_FILE_NAME' configuration macro,
     if specified.
   * `ld' in the compiler's search directories.
   * `TARGET-ld' in `PATH'.
   `collect2' explicitly avoids running `ld' using the file name under
which `collect2' itself was invoked.  In fact, it remembers up a list
of such names--in case one copy of `collect2' finds another copy (or
version) of `collect2' installed as `ld' in a second place in the
search path.
   `collect2' searches for the utilities `nm' and `strip' using the
same algorithm as above for `ld'.