syms(FP)                       6 January 1993                       syms(FP)


 Name

    syms - common object file symbol table format

 Syntax


    #include  <syms.h>


 Description

    Common object files contain information to support symbolic software
    testing (see sdb(CP)).  Line number entries, linenum(FP), and extensive
    symbolic information permit testing at the C source level.  Every object
    file's symbol table is organized as shown below.

              File name 1.
                      Function 1.
                              Local symbols for function 1.
                      Function 2.
                              Local symbols for function 2.
                      ...
                      Static externs for file 1.

              File name 2.
                      Function 1.
                              Local symbols for function 1.
                      Function 2.
                              Local symbols for function 2.
                      ...
                      Static externs for file 2.
              ...

              Defined global symbols.
              Undefined global symbols.

    The entry for a symbol is a fixed-length structure.  The members of the
    structure hold the name (null padded), its value, and other information.
    The C structure follows:


    #define  SYMNMLEN      8
    #define  FILNMLEN      14
    #define  DIMNUM        4

    struct  syment
    {
        union                                 /* all ways to get symbol name */
        {
            char        _n_name[SYMNMLEN];    /* symbol name */
            struct
            {
                long    _n_zeroes;            /* == 0L when in string table */
                long    _n_offset;            /* location of name in table */
            } _n_n;
            char        *_n_nptr[2];          /* allows overlaying */
        } _n;
        long            n_value;              /* value of symbol */
        short           n_scnum;              /* section number */
        unsigned short  n_type;               /* type and derived type */
        char            n_sclass;             /* storage class */
        char            n_numaux;             /* number of aux entries */
    };

    #define  n_name     _n._n_name
    #define  n_zeroes   _n._n_n._n_zeroes
    #define  n_offset   _n._n_n._n_offset
    #define  n_nptr     _n._n_nptr[1]


    Meaningful values and their explanations are given in both syms.h and
    Common Object File Format (COFF).  To interpret the entries see these
    sources.  Some symbols require more information than a single entry; they
    are followed by auxiliary entries that are the same size as a symbol
    entry.  The format follows.

       union auxent
       {
           struct
           {
               long        x_tagndx;
               union
               {
                   struct
                   {
                       unsigned short  x_lnno;
                       unsigned short  x_size;
                   } x_lnsz;
                   long    x_fsize;
               } x_misc;
               union
               {
                   struct
                   {
                       long    x_lnnoptr;
                       long    x_endndx;
                   }   x_fcn;
                   struct
                   {
                       unsigned short  x_dimen[DIMNUM];
                   }   x_ary;
               }   x_fcnary;
               unsigned short  x_tvndx;
           }   x_sym;

           union
           {
               char    x_fname[FILNMLEN];
               struct
               {
                   long x_zero;
                   long x_offset;
               }   x_longname;
           }   x_file;

           struct
           {
               long    x_scnlen;
               unsigned short  x_nreloc;
               unsigned short  x_nlinno;
           }   x_scn;

           struct
           {
               long            x_tvfill;
               unsigned short  x_tvlen;
               unsigned short  x_tvran[2];
           }   x_tv;
       };


    Indexes of symbol table entries begin at zero.

 Notes

    On machines on which ints are equivalent to longs, all longs have their
    type changed to int.  Thus the information about which symbols are
    declared as longs and which as ints does not show up in the symbol table.

 See also

    a.out(FP), linenum(FP), sdb(CP)