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      NNNNAAAAMMMMEEEE
           stab - symbol table types

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      DDDDEEEESSSSCCCCRRRRIIIIPPPPTTTTIIIIOOOONNNN
           _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 ddddbbbbxxxx
           debugger.  Symbol table entries can be produced by the _s_t_a_b_s
           assembler directive.  This allows one to specify a double-
           quote delimited 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 directive
           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(_4), 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 */



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           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 ddddbbbbxxxx symbolic debugger uses the following
           n_type values:

           /* This file gives definitions supplementing <a.out.h>
            * for permanent symbol table entries.
            * These must have one of the N_STAB bits on,
            * and are subject to relocation according to the masks in <a.out.h>.
            *
            * for symbolic debugger, dbx(1):
            */
           #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 */
           /*
            * for the berkeley pascal compiler, pc(1):
            */
           #define   N_PC 0x30      /* global pascal symbol: name,,0,subtype,line */

           _D_b_x uses the n_desc field to hold a type specifier in the
           form used by the Portable C Compiler, _c_c(1), in which a base



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           type is qualified in the following structure:

           struct desc {
                   short  q6:2,
                          q5:2,
                          q4:2,
                          q3:2,
                          q2:2,
                          q1:2,
                          basic:4;
           };

           There are four qualifications, with q1 the most significant
           and q6 the least significant:
                0    none
                1    pointer
                2    function
                3    array
           The sixteen basic types are assigned as follows:
                0    undefined
                1    function argument
                2    character
                3    short
                4    int
                5    long
                6    float
                7    double
                8    structure
                9    union
                10   enumeration
                11   member of enumeration
                12   unsigned character
                13   unsigned short
                14   unsigned int
                15   unsigned long

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           as(1), ld(1), dbx(1), a.out(4)

















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