stab(4)stab(4)NAMEstab - Symbol table types
SYNOPSIS
#include <stab.h>
DESCRIPTION
The stab.h header file defines some values of the n_type field of the
symbol table of a.out files. These are the types for permanent symbols
(that is, not local labels, etc.) used by the old debugger sdb. Symbol
table entries can be produced by the 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 directive can be used to implicitly address the
current location. If no name is needed, symbol table entries can be
generated using the directive. The loader promises to preserve the
order of symbol table entries produced by directives. An element of the
symbol table consists of the following structure:
/* SYMBOL INFORMATION ENTRY* This is used for defined symbols, imports
and stabs. The type (kind)* of the associated symbols load command
determines which.*/ typedef struct symbol_info_t {
union {mo_offset_t symbol_name;
mo_ptr_t symbol_nameP;
} si_name;
mo_short_t si_package_index;
mo_short_t si_type;
mo_short_t si_flags;
mo_byte_t si_reserved byte;
mo_byte_t si_sc_type;
union {mo_addr_t def_val; /* defined section, offset */
mo_long_t imp_val; /* index in import list */
mo_long_t lit_val; /* literal value */
mo_vm_addr_t abs_val; /* absolute value */
} si_value;
} symbol_info_t;
The low bits of the si_sc_type field are used to place a symbol into at
most one segment, according to the following masks. A symbol can be in
none of these segments by having none of these segment bits set.
* Simple values for si_sc_type. */ #define N_UNDF 0x0 /* unde‐
fined */ #define N_ABS 0x2 /* absolute */
#define N_TEXT 0x4 /* text */ #define N_DATA 0x6 /* data */
#define N_BSS 0x8 /* bss */ #define N_EXT 01 /* exter‐
nal bit, or'ed in */
The n_value field of a symbol is relocated by the linker, ld, as an
address within the appropriate segment. The 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
si_sc_type field has one of the following bits set:
#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, sdb, uses the following n_type values:
#define N_GSYM 0x20 /* global symbol: name,,0,type,0 */
#define N_FNAME 0x22 /* procedurename(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 /* sourcefilename: name,,0,0,address */
#define N_LSYM 0x80 /* local sym: name,,0,type,offset */
#define N_SOL 0x84 /* #includedfilename: 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,nestinglevel,address */
#define N_RBRAC 0xe0 /* right bracket: 0,,0,nestinglevel,address */
#define N_BCOMM 0xe2 /* begincommon: name,, */
#define N_ECOMM 0xe4 /* endcommon: name,, */
#define N_ECOML 0xe8 /* endcommon(local name): ,,address */
#define N_LENG 0xfe /* secondstabentrywithlengthinformation */
The comments give sdb conventional use for n_name, n_other, n_desc, and
n_value fields of the given n_type. The sdb debugger uses the n_desc
field to hold a type specifier in the form used by the Portable C Com‐
piler, cc.
The Berkeley Pascal compiler, pc, uses the following si_sc_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: Source filename Included filename Global label Global
constant Global type Global variable Global function Global procedure
External function External procedure Library variable "12" Library rou‐
tine
SEE ALSO
Commands: as(1), ld(1)stab(4)
