man Pages(4): File Formats

filehdr(4)

NAME | SYNOPSIS | DESCRIPTION | SEE ALSO

NAME

filehdr- file header for common object files

SYNOPSIS

#include <filehdr.h>

DESCRIPTION

Every common object file begins with a 20-byte header. The following C struct declaration is used:

struct  filehdr
{
	unsigned short	f_magic ;	/* magic number */
	unsigned short	f_nscns ;	/* number of sections */
	long		f_timdat ;	/* time & date stamp */
	long		f_symptr ;	/* file ptr to symtab */
	long		f_nsyms ;	/* number of symtab entries */
	unsigned short	f_opthdr ;	/* sizeof(opt and header) */
	unsigned short	f_flags ;	/* flags */
};

f_symptr is the byte offset into the file at which the symbol table can be found. Its value can be used as the offset in fseek(3S) to position an I/O stream to the symbol table. The UNIX system optional header is 28 bytes. The valid magic numbers are given below:

#define	I386MAGIC	0514	/* i386 Computer */
#define	WE32MAGIC	0560	/* 3B2, 3B5, and 3B15 computers */
#define	N3BMAGIC	0550	/* 3B20 computer */
#define	NTVMAGIC	0551	/* 3B20 computer */
#define	VAXWRMAGIC	0570	/* VAX writable text segments */
#define	VAXROMAGIC	0575	/* VAX read only sharable
			text segments */

The value in f_timdat is obtained from the time(2) system call. Flag bits currently defined are:

#define	F_RELFLG	0000001	/* relocation entries stripped */
#define	F_EXEC	0000002	/* file is executable */
#define	F_LNNO	0000004	/* line numbers stripped */
#define	F_LSYMS	0000010	/* local symbols stripped */
#define	F_AR16WR	0000200	/* 16-bit DEC host */
#define	F_AR32WR	0000400	/* 32-bit DEC host */
#define	F_AR32W	0001000	/* non-DEC host */
#define	F_BM32ID	0160000	/* WE32000 family ID field */
#define	F_BM32B	0020000	/* file contains WE 32100 code */
#define	F_BM32MAU	0040000	/* file reqs MAU to execute */
#define	F_BM32RST	0010000	/* this object file contains restore
			work around [3B5/3B2 only] */