stab(5)stab(5)Namestab - symbol table types
Syntax
#include <stab.h>
Description
The file defines some values of the n_type field of the symbol table of
files. These are the types for permanent symbols (that is, not local
labels, and so on) used by the debugger and the Berkeley Pascal com‐
piler Symbol table entries can be produced by the assembler directive,
which allows you 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
.stabd directive can be used to implicitly address the current loca‐
tion. If no name is needed, symbol table entries can be generated
using the .stabn directive. The loader promises to preserve the order
of symbol table entries produced by .stab directives. As described in
an element of the symbol table consists of the following structure:
/*
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 one
segment, maximum, according to the following masks defined in If none
of the segment bits are set, a symbol cannot be in any of these seg‐
ments.
* 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, 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 dis‐
card 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 C compiler
generates the following n_type values, where the comments give the use
for .stabs and the n_name, n_other, n_desc, and n_value fields of the
given n_type:
#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 /* struct 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 /* alt entry: name,linenumber,address */
#define N_LBRAC 0xc0 /* lft bracket: 0,,0,nesting level,address */
#define N_RBRAC 0xe0 /* rt 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 */
The n_desc holds a type specifier in the form used by the Portable C
Compiler, in which a base 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 4 qualifications, with q1 the most significant and q6 the
least significant:
0 None
1 Pointer
2 Function
3 Array
The 16 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
The same information is encoded in a more useful form in the symbolic
string. The symbol's name is followed by a colon, which is followed by
a description of the symbol's type. This begins with one of the fol‐
lowing letters:
c Constant
f Local function
F Function name
G Global variable
p Argument (by value)
P External procedure
r Register variable
s Static variable
t Typedef name
T Local variable
v Argument (by ref)
V Local static variable
No letter
Local dynamic variable
This is followed by the variable's type, where type is any of the fol‐
lowing:
integer Same as previously defined type integer
integer=type Define type integer to have form type
*type Pointer to type
rtype;low;high; Range of type from low to high
arangetype Array with bounds range of type
ename:value,; Enumerated type. The phrase "name:value," repeats as
needed.
ssizename:type,offset,size;;
Structure. The size is the number of bytes in the com‐
plete structure. The phrase "name:type,offset,size;"
repeats as needed, giving the offset from the start of
the structure (in bits) and the size in bits of each
member.
usizename:type,offset,size;;
Union. Analogous to structure entry.
Stype Set of type.
ftype,integer;type,class;
Function returning type with integer parameters,
described by the repeating "type,class;" phrase.
pinteger;type,class;
Procedure-like function
dtype File of type
The Berkeley Pascal compiler, uses the following n_type value:
#define N_PC 0x30 /* global pascal symbol: name,,0,subtype,line */
The complier 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 Alsoas(1), cc(1), dbx(1), ld(1), pc(1), a.out(5)
VAX stab(5)
