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scnhdr(4)
NAME
  scnhdr - Section header for an object file

SYNOPSIS
  #include <scnhdr.h>

DESCRIPTION
  Every object file has a group of section headers to specify the layout of
  the data within the file.  Each section within an object file has its own
  header.  The C structure is as follows:

  struct scnhdr
  {
   char s_name[8]; /* section name */
   long s_paddr; /* physical address, aliased s_nlib */
   long s_vaddr; /* virtual address */
   long s_size; /* section size */
   long s_scnptr; /* file ptr to raw data for section */
   long s_relptr; /* file ptr to relocation */
   long s_lnnoptr; /* special purpose */
   unsigned short s_nreloc; /* number of reloc entries */
   unsigned short s_nlnno; /* unused */
   int s_flags; /* flags */
  };

  File pointers are byte offsets into the file; they can be used as the
  offset in a call to FSEEK (see ldfcn(4)).  If a section is initialized, the
  file contains the actual bytes.  An uninitialized section is somewhat
  different.  It has a size, symbols defined in it, and symbols that refer to
  it.  But it can have no relocation entries or data.  Consequently, an
  uninitialized section has no raw data in the object file, and the values
  for s_scnptr, s_relptr, and s_nreloc are zero.

  The entries that refer to line numbers (s_lnnoptr, and s_nlnno) are not
  related to line number information.  See the header file sym.h for the
  entries to get to the line number table.  The entries that were for line
  numbers are reserved and should be set to zero.

  The number of relocation entries for a section is found in the s_nreloc
  field of the section header. Being a `C' language short, this field can
  overflow with large objects.	If this field overflows, the section header
  s_flags field has the SM S_NRELOC_OVFL bit set.  In this case, the true
  number of relocation entries is found in the r_vaddr field of the first
  relocation entry for that section.  That relocation entry has a type of SM
  R_ABS, so it is ignored when the relocation takes place.

RELATED INFORMATION
  ld(1), fseek(3), a.out(4), reloc(4).

Index for Section 4

Alphabetical listing for S

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