reloc(5) [ultrix 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)

Check Out this Related Man Page

MACH-O(5)							File Formats Manual							 MACH-O(5)

NAME

       Mach-O - Mach-O assembler and link editor output

SYNOPSIS

       #include <mach-o/loader.h>
       #include <mach-o/nlist.h>
       #include <mach-o/stab.h>
       #include <mach-o/reloc.h>

DESCRIPTION

       The  object  files  produced  by the assembler and link editor are in Mach-O (Mach object) file format.	The file name a.out is the default
       output file name of the assembler as(1) and the link editor ld(1) The format of the object file however is not 4.3BSD a.out format  as  the
       name  suggests,	but  rather  Mach-O  format.  The link editor will make a.out executable if the resulting format is an executable type and
       there were no errors and no unresolved external references.

       The complete description of a Mach-O file is given in a number of include files.  The file <mach-o/loader.h> describes the headers,  <mach-
       o/nlist.h> describes the symbol table entries with <mach-o/stab.h> supplementing it, and <mach-o/reloc.h> describes the relocation entries.

       The  actual  instructions and data used by the program represented by a Mach-O file are the contents of its sections.  Sections are grouped
       together in segments.  Each section carries with it, in its header, the information as to which segment it belongs in.  When  a	file  type
       that  is  executable  is  created  the sections are placed in their proper segment and all the segment headers are created and the segments
       themselves are padded out to the segment alignment (typically the target pagesize).  For the object file type produced by an assembler  (or
       by the link editor for further linking) all the sections are placed in one segment for compactness.

       When  the  kernel executes a Mach-O file it maps in the object file's segments, the dynamic link editor (if used) and creates the thread(s)
       for execution.  Any part of the object file that is not part of a segment is not mapped in for execution.  For executable using the dynamic
       link  editor  the  headers  and other link edit information is needed to execute the file.  These parts include the relocation entries, the
       symbol table and the string table.  These parts are mapped in with the use of the link editor's -seglinkedit option which creates a segment
       that contains these parts.  These parts can be stripped down with the -S option to ld(1) or various options to strip(1).

SEE ALSO

       as(1), ld(1), nm(1), gdb(1), stab(5), strip(1)

Apple Computer, Inc.						 October 22, 2001							 MACH-O(5)

Linux and UNIX Man Pages

reloc(5) [ultrix man page]

Check Out this Related Man Page