stab.5

来自「<B>Digital的Unix操作系统VAX 4.2源码</B>」· 5 代码 · 共 297 行

.SCCSID: @(#)stab.5	2.1	3/10/87
.TH stab 5 VAX
.SH Name
stab \- symbol table types
.SH Syntax
.B "#include <stab.h>"
.SH Description
.NXB "stab file" "format"
.NXA "a.out file" "stab file"
The
.PN stab.h
file
defines some values of the n_type field of the symbol table of
.PN a.out
files.
These are the types for permanent symbols
(that is, not local labels, and so on)
used by the debugger
.PN dbx
and the Berkeley Pascal compiler 
.MS pc 1 .
Symbol table entries can be produced by the 
.PN .stabs
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).
.PP
To avoid having to produce an explicit label for the address field,
the .stabd
directive can be used to implicitly address the current location.
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 
.MS a.out 5 ,
an element of the symbol table
consists of the following structure:
.EX 0
/*
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 */
};
.EE
.PP
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 
.PN <a.out.h> .
If none of the segment bits are set, a symbol cannot be in any of these
segments.
.EX 0
* 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 */
.EE
.PP
The n_value field of a symbol is relocated by the linker,
.PN ld ,
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:
.EX 0
/*
* 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 */
.EE
.PP
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
.IR .stab s
and the n_name, n_other, n_desc, and n_value fields
of the given n_type: 
.EX 0
#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 */
.EE
.PP
The
n_desc holds a type specifier in the form used
by the Portable C Compiler,
.MS cc 1 ,
in which a base type is qualified in the following structure:
.EX 0
struct desc {
	short	q6:2,
		q5:2,
		q4:2,
		q3:2,
		q2:2,
		q1:2,
		basic:4;
};
.EE
.PP
There are 4 qualifications, with q1 the most significant and q6 the least
significant:
.sp 4p
.RS 3
.PD 0
.IP 0 5
None
.IP 1
Pointer
.IP 2
Function
.IP 3
Array
.RE
.PD
.PP
The 16 basic types are assigned as follows:
.sp 4p
.PD 0
.RS 3
.IP 0 5
Undefined
.IP 1
Function argument
.IP 2
Character
.IP 3
Short
.IP 4
Int
.IP 5
Long
.IP 6
Float
.IP 7
Double
.IP 8
Structure
.IP 9
Union
.IP 10
Enumeration
.IP 11
Member of enumeration
.IP 12
Unsigned character
.IP 13
Unsigned short
.IP 14
Unsigned int
.IP 15
Unsigned long
.RE
.PD 
.PP
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 following letters:
.sp 4p
.RS 3
.PD 0
.IP c
Constant
.IP f
Local function
.IP F
Function name
.IP G
Global variable
.IP p
Argument (by value)
.IP P
External procedure
.IP r
Register variable
.IP s
Static variable
.IP t 5 
Typedef name
.IP T
Local variable
.IP v
Argument (by ref)
.IP V
Local static variable
.IP "No letter"
Local dynamic variable
.RE
.PD
.PP
This is followed by the variable's type, where \fItype\fR is any of
the following:
.IP \fIinteger\fR 16
Same as previously defined type \fIinteger\fR
.IP \fIinteger\fR=\fItype\fR
Define type \fIinteger\fR to have form \fItype\fI
.IP *\fItype\fR
Pointer to \fItype\fR
.IP r\fItype\fR;\fIlow\fR;\fIhigh\fR;
Range of \fItype\fR from \fIlow\fR to \fIhigh\fR
.IP a\fIrangetype\fR
Array with bounds \fIrange\fR of \fItype\fR
.IP e\fIname:value\fR,;
Enumerated type.  The phrase "\fIname\fR:\fIvalue\fR," repeats as needed.
.IP s\fIsizename\fR:\fItype,offset,size\fR;;
.br
Structure.  The \fIsize\fR is the number of bytes in the
complete structure.  The phrase "\fIname:\fItype,offset,size\fR;"
repeats as needed, giving the \fIoffset\fR from the start of the
structure (in bits) and the \fIsize\fR in bits of each member.
.IP u\fIsizename\fR:\fItype,offset,size\fR;;
Union.  Analogous to structure entry.
.IP S\fItype\fR
Set of \fItype\fR.
.IP f\fItype,integer\fR;\fItype,class\fR;	
Function returning \fItype\fR with \fIinteger\fR parameters, described
by the repeating "\fItype,class\fR;" phrase.
.IP p\fIinteger\fR;\fItype,class\fR;
Procedure\-like function
.IP d\fItype\fR
File of \fItype\fR
.RE
.PP
The Berkeley Pascal compiler,
.MS pc 1 ,
uses the following n_type value:
.PP
.EX
#define	N_PC	0x30	/* global pascal symbol: name,,0,subtype,line */
.EE
.PP
The complier uses the following subtypes to do type checking across separately
compiled files:
.sp 4p
.RS 3
.PD 0
.IP 1 5
Source file name
.IP 2
Included file name
.IP 3
Global label
.IP 4
Global constant
.IP 5
Global type
.IP 6
Global variable
.IP 7
Global function
.IP 8
Global procedure
.IP 9
External function
.IP 10
External procedure
.IP 11
Library variable
.IP 12
Library routine
.PD
.SH See Also
as(1), cc(1), dbx(1), ld(1), pc(1), a.out(5)
.NXE "stab file" "format"