filehdr(FP)                    6 January 1993                    filehdr(FP)


 Name

    filehdr - file header for common object files

 Syntax


    #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 ;        /* # symtab entries */
       unsigned short      f_opthdr ;       /* sizeof(opt hdr) */
       unsigned short      f_flags ;        /* flags */
       } ;

    fsymptr 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(S) 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 I286SMAGIC      0512 /* 80286 computers-small model programs */
       #define I286LMAGIC      0522 /* 80286 computers-large model programs */
       #define I386MAGIC       0514 /* 80386 computers */
       #define FBOMAGIC        0560 /* 3B2 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 */

    The value in ftimdat is obtained from the time(S) 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_MINMAL        0000020 /* minimal object file */
       #define F_UPDATE        0000040 /* update file, ogen produced */
       #define F_SWABD         0000100 /* file is "pre-swabbed" */
       #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_PATCH         0002000 /* "patch" list in opt hdr */
       #define F_80186         010000  /* contains 80186 instructions */
       #define F_80286         020000  /* contains 80286 instructions */
       #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 */


 See also

    a.out(FP), fseek(S), time(S)