STAB(5)                                                                STAB(5)



NAME
       stab - symbol table types

SYNOPSIS
       #include <stab.h>

DESCRIPTION
       _S_t_a_b_._h  defines  some values of the n_type field of the symbol table of
       a.out files.  These are the types for permanent symbols (i.e. not local
       labels,  etc.)   used  by  the old debugger _s_d_b and the Berkeley Pascal
       compiler _p_c(1).  Symbol table entries can be  produced  by  the  _._s_t_a_b_s
       assembler  directive.  This allows one to specify a double-quote delim‐
       ited name, a symbol type, one char and one short of  information  about
       the symbol, and an unsigned long (usually an address).  To avoid having
       to produce an explicit label for the address field, the  _._s_t_a_b_d  direc‐
       tive  can  be  used  to implicitly address the current location.  If no
       name is needed, symbol table entries can be generated using the  _._s_t_a_b_n
       directive.   The  loader promises to preserve the order of symbol table
       entries produced by _._s_t_a_b directives.  As  described  in  _a_._o_u_t(5),  an
       element of the symbol table consists of the following structure:

       /*
        * Format of a symbol table entry.
        */
       struct nlist {
               union {
                        char  *n_name; /* for use when in-core */
                        long  n_strx;  /* index into file string table */
               } n_un;
               unsigned char  n_type;  /* type flag */
               char           n_other; /* unused */
               short          n_desc;  /* see struct desc, below */
               unsigned n_value;       /* address or offset or line */
       };

       The  low  bits  of  the n_type field are used to place a symbol into at
       most  one  segment,  according  to  the  following  masks,  defined  in
       <_a_._o_u_t_._h>.  A symbol can be in none of these segments by having none of
       these segment bits set.

       /*
        * Simple values for n_type.
        */
       #define N_UNDF  0x0   /* undefined */
       #define N_ABS   0x2   /* absolute */
       #define N_TEXT  0x4   /* text */
       #define N_DATA  0x6   /* data */
       #define N_BSS   0x8   /* bss */

       #define N_EXT   01    /* external bit, or’ed in */

       The n_value field of a symbol is relocated by the linker, _l_d(1)  as  an
       address  within the appropriate segment.  N_value fields of symbols not
       in any segment are unchanged by the linker.  In  addition,  the  linker
       will discard certain symbols, according to rules of its own, unless the
       n_type field has one of the following bits set:

       /*
        * Other permanent symbol table entries have some of the N_STAB bits set.
        * These are given in <stab.h>
        */
       #define N_STAB        0xe0/* if any of these bits set, don’t discard */


       This allows up to 112 (7 ∗ 16) symbol types, split between the  various
       segments.   Some  of these have already been claimed.  The old symbolic
       debugger, _s_d_b, uses the following n_type values:

       #define N_GSYM  0x20  /* global symbol: name,,0,type,0 */
       #define N_FNAME 0x22  /* procedure name (f77 kludge): name,,0 */
       #define N_FUN   0x24  /* procedure: name,,0,linenumber,address */
       #define N_STSYM 0x26  /* static symbol: name,,0,type,address */
       #define N_LCSYM 0x28  /* .lcomm symbol: name,,0,type,address */
       #define N_RSYM  0x40  /* register sym: name,,0,type,register */
       #define N_SLINE 0x44  /* src line: 0,,0,linenumber,address */
       #define N_SSYM  0x60  /* structure elt: name,,0,type,struct_offset */
       #define N_SO    0x64  /* source file name: name,,0,0,address */
       #define N_LSYM  0x80  /* local sym: name,,0,type,offset */
       #define N_SOL   0x84  /* #included file name: name,,0,0,address */
       #define N_PSYM  0xa0  /* parameter: name,,0,type,offset */
       #define N_ENTRY 0xa4  /* alternate entry: name,linenumber,address */
       #define N_LBRAC 0xc0  /* left bracket: 0,,0,nesting level,address */
       #define N_RBRAC 0xe0  /* right bracket: 0,,0,nesting level,address */
       #define N_BCOMM 0xe2  /* begin common: name,, */
       #define N_ECOMM 0xe4  /* end common: name,, */
       #define N_ECOML 0xe8  /* end common (local name): ,,address */
       #define N_LENG  0xfe  /* second stab entry with length information */

       where the comments give _s_d_b conventional use for _._s_t_a_bs and the n_name,
       n_other,  n_desc, and n_value fields of the given n_type.  _S_d_b uses the
       n_desc field to hold a type specifier in the form used by the  Portable
       C  Compiler, _c_c(1); see the header file _p_c_c_._h for details on the format
       of these type values.

       The Berkeley Pascal compiler, _p_c(1), uses the following n_type value:

       #define N_PC    0x30  /* global pascal symbol: name,,0,subtype,line */

       and uses the following subtypes to do type checking  across  separately
       compiled files:
               1       source file name
               2       included file name
               3       global label
               4       global constant
               5       global type
               6       global variable
               7       global function
               8       global procedure
               9       external function
               10      external procedure
               11      library variable
               12      library routine

SEE ALSO
       as(1), ld(1), dbx(1), a.out(5)

BUGS
       More basic types are needed.



4th Berkeley Distribution        May 19, 1986                          STAB(5)