4.4BSD/usr/share/man/cat5/stab.0
STAB(5) BSD Programmer's Manual STAB(5)
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ssttaabb - symbol table types
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The file <_s_t_a_b_._h> defines some of the symbol table _n___t_y_p_e field values
for a.out files. These are the types for permanent symbols (i.e. not lo-
cal labels, etc.) used by the old debugger _s_d_b and the Berkeley Pascal
compiler pc(1). Symbol table entries can be produced by the _._s_t_a_b_s as-
sembler directive. This allows one to specify a double-quote delimited
name, a symbol type, one char and one short of information about the sym-
bol, and an unsigned long (usually an address). To avoid having to pro-
duce 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.out(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___t_y_p_e 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___v_a_l_u_e field of a symbol is relocated by the linker, ld(1) as an ad-
dress within the appropriate segment. _N___v_a_l_u_e 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___t_y_p_e
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 de-
bugger, _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_b _s and the _n___n_a_m_e,
_n___o_t_h_e_r, _n___d_e_s_c, and _n___v_a_l_u_e fields of the given _n___t_y_p_e. _S_d_b uses the
_n___d_e_s_c field to hold a type specifier in the form used by the Portable C
Compiler, cc(1); see the header file _p_c_c_._h for details on the format of
these type values.
The Berkeley Pascal compiler, pc(1), uses the following _n___t_y_p_e 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
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as(1), ld(1), dbx(1), a.out(5)
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More basic types are needed.
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The ssttaabb file appeared in 4.0BSD.
4th Berkeley Distribution June 5, 1993 2