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filehdr(5) [ultrix man page]

filehdr(5)							File Formats Manual							filehdr(5)

Name
       filehdr - file header for RISC object files

Syntax
       #include < filehdr.h>

Description
       Every RISC 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 pointer to symbolic header */
	  long		  f_nsyms;     /* sizeof(symbolic header) */
	  unsigned short  f_opthdr;    /* sizeof(optional header) */
	  unsigned short  f_flags;     /* flags */
       };

       The byte offset into the file at which the symbolic header can be found is f_symptr.  Its value can be used as the offset in to position an
       I/O stream to the symbolic header.  The ULTRIX system optional header is 56 bytes.  The valid magic numbers are given below:
       #define MIPSEBMAGIC 0x0160 /* objects for big-endian machines */
       #define MIPSELMAGIC 0x0162 /* objects for little-endian machines */
       #define MIPSEBUMAGIC 0x0180 /* ucode objects for big-endian machines */
       #define MIPSELUMAGIC 0x0182 /* ucode objects for little-endian machines */
       RISC object files can be loaded and examined on machines differing from the object's target byte sex.  Therefore,  for  object  file  magic
       numbers, the byte-swapped values have define constants associated with them:
       #define SMIPSEBMAGIC 0x6001
       #define SMIPSELMAGIC 0x6201
       The value in f_timdat is obtained from the system call.	Flag bits used in RISC objects 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 */

See Also
       time(2), fseek(3s), a.out(5)

								       RISC								filehdr(5)

Check Out this Related Man Page

reloc(5)							File Formats Manual							  reloc(5)

Name
       reloc - relocation information for a MIPS object file

Syntax
       #include <reloc.h>

Description
       Object  files  have one relocation entry for each relocatable reference in the text or data.  If relocation information is present, it will
       be in the following format:

       struct	reloc
       {
	  long	    r_vaddr ;	       /* (virtual) address of reference */
	  long	    r_symndx ;	       /* index into symbol table */
	  ushort    r_type ;	       /* relocation type */
	  unsigned  r_symndx:24,       /* index into symbol table */
		    r_reserved:3,
		    r_type:4,	       /* relocation type */
		    r_extern:1;        /* if 1 symndx is an index into the
					  external symbol table, else symndx
					  is a section # */
       } ;

       /* Relocation types */

       #define	R_ABS	    0
       #define	R_REFHALF   1
       #define	R_REFWORD   2
       #define	R_JMPADDR   3
       #define	R_REFHI     4
       #define	R_REFLO     5
       #define	R_GPREL     6
       #define	R_LITERAL   7

       /* Section numbers */

       #define	R_SN_NULL   0
       #define	R_SN_TEXT   1
       #define	R_SN_RDATA  2
       #define	R_SN_DATA   3
       #define	R_SN_SDATA  4
       #define	R_SN_SBSS   5
       #define	R_SN_BSS    6
       #define	R_SN_INIT   7
       #define	R_SN_LIT8   8
       #define	R_SN_LIT4   9

       The link editor reads each input section and performs relocation.  The relocation entries direct how references found within the input sec-
       tion are treated.

       If  is zero, it is a local relocation entry and then is a section number (R_SN_*).  For these entries, the starting address for the section
       referenced by the section number is used in place of an external symbol table entry's value.  The assembler and	loader	always	use  local
       relocation entries if the item to be relocated is defined in the object file.

       For  every  external  relocation (except R_ABS) a signed constant is added to the symbol's virtual address that the relocation entry refers
       to.  This constant is assembled at the address being relocated.

       R_ABS	      The reference is absolute and no relocation is necessary.  The entry will be ignored.

       R_REFHALF      A 16-bit reference to the symbol's virtual address.

       R_REFWORD      A 32-bit reference to the symbol's virtual address.

       R_JMPADDR      A 26-bit jump instruction reference to the symbol's virtual address.

       R_REFHI	      A reference to the high 16 bits of the symbol's virtual address.	The  next  relocation  entry  must  be	the  corresponding
		      R_REFLO entry, so the proper value of the constant to be added to the symbol's virtual address can be reconstructed.

       R_REFLO	      A reference to low 16 bits to the symbol's virtual address.

       R_GPREL	      A 16-bit offset to the symbol's virtual address from the global pointer register.

       R_LITERAL      A 16-bit offset to the literal's virtual address from the global pointer register.

       Relocation  entries  are generated automatically by the assembler and automatically used by the link editor.  Link editor options exist for
       both preserving and removing the relocation entries from object files.

       The number of relocation entries for a section is found in the field of the section header.  This field is a C language short and can over-
       flow  with  large objects.  If this field overflows, the section header field has the S_NRELOC_OVFL bit set.  In this case, the true number
       of relocation entries is found in the field of the first relocation entry for that section.  That relocation entry has a type of R_ABS,	so
       it is ignored when the relocation takes place.

See Also
       as(1), ld(1), a.out(5), syms(5), scnhdr(5)

								       RISC								  reloc(5)
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