Using and Porting GNU CC
Using and Porting GNU CC
collect2
Many target systems do not have support in the assembler and linker for
``constructors''---initialization functions to be called before the
official ``start'' of main. On such systems, GNU CC uses a
utility called collect2 to arrange to call these 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.
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.
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.