NAME

crt0.o, gcrt0.o, mcrt0.o, frt0.o, gfrt0.o, mfrt0.o − execution startup routines

DESCRIPTION

The C and Pascal compilers link in files crt0.o, gcrt0.o, or mcrt0.o to provide startup capabilities and environment for program execution.  All are identical except that gcrt0.o and mcrt0.o provide additional functionality for gprof(1) and prof(1) profiling support respectively. Similarly, the FORTRAN compiler links in either frt0.o, gfrt0.o, or mfrt0.o. 

The following symbols are defined in these routines:

__argc_value A variable of type int containing the number of arguments. 

__argv_value An array of character pointers to the arguments themselves. 

_environ An array of character pointers to the environment in which the program will run. This array is terminated by a null pointer. 

_SYSTEM_ID A variable of type int containing the system id value for an executable program. 

DEPENDENCIES

Series 300/400

The symbols above are shown as they are visible from C.  To access them from assembly language, add an additional underscore to the beginning of the symbol.  For example, an assembly language program refers to __argc_value as ___argc_value. 

Series 300/400 startup files also define the following symbols which are listed as when used from assembly language.  The state of these variables can be determined from C by using other library routines (see is_hw_present(3C)).

flag_68010 A variable of type short.  Non-zero if the processor is a 68010; zero if not. 

float_soft A variable of type short.  Zero if the HP98635 floating-point card is present; non-zero if it is not present.

float_loc A constant defining the location in memory of the HP98635 floating-point card.

flag_68881 A variable of type short.  Non-zero if the HP68881 floating-point coprocessor is present; zero if it is not present.

flag_fpa A variable of type short.  Non-zero if the HP98248 floating-point card is present; zero if it is not present.

fpa_loc A constant defining the location in memory of the HP98248 floating-point card.

Series 700/800

All compilers on Series 700 and 800 use the crt0.o, gcrt0.o, or mcrt0.o file; the files frt0.o, gfrt0.o, and mfrt0.o do not exist. 

The Series 700 and 800 start-up files also define the following additional symbols:

$START$ Execution start address. 

_start A secondary startup routine for C programs, called from $START$, which in turn calls main.  This routine is contained in the C library rather than the crt0.o file.  For Pascal and FORTRAN programs, this symbol labels the beginning of the outer block (main program) and is generated by the compilers. 

$global$ The initial address of the program’s data pointer.  The startup code loads this address into general register 27. 

$UNWIND_START The beginning of the stack unwind table. 

$UNWIND_END The end of the stack unwind table. 

$RECOVER_START The beginning of the try/recover table. 

$RECOVER_END The end of the try/recover table. 

The crt0.o file defines a null procedure for _mcount, so programs compiled with profiling can be linked without profiling. 

The linker defines the following two symbols:

__text_start The beginning address of the program’s text area. 

__data_start The beginning address of the program’s data area. 

AUTHOR

The features described in this entry originated from AT&T UNIX System III. 

SEE ALSO

cc(1), f77(1), ld(1), pc(1), prof(1), gprof(1), pc(1), profil(2), exec(2), is_hw_present(3C), monitor(3C). 

Hewlett-Packard Company  —  HP-UX Release 9.0: August 1992