Path: utzoo!mnetor!uunet!husc6!yale!cmcl2!brl-adm!adm!feldman%vger@gswd-vms.Gould.COM
From: feldman%vger@gswd-vms.Gould.COM (Mike Feldman)
Newsgroups: comp.unix.wizards
Subject: any comp.dbx.wizards out there?
Message-ID: <11139@brl-adm.ARPA>
Date: 6 Jan 88 19:05:25 GMT
Sender: news@brl-adm.ARPA
Lines: 166

/*
 * Question:
 * From dbx, when 'foo_type' is a typedef'd structure, and foo is a foo_type,
 * if I tell dbx to print foo, where does it gets it's information as to
 * where the fields are in foo?
 *
 * Answer:
 * dbx gets its information from the compiler through the .stab information
 * that is generated when you specify the "-g" option.  For example, in the
 * following test program:
 */

#define BIG_NUM	8

typedef struct {
	int	array1[BIG_NUM];
	char	a, b, c, d, e;
	int	array2[BIG_NUM];
} foo_type;

foo_type foo;

main(argc,argv)
 int argc;
 char *argv[];
{
	printf("hello world\n");
}

/*
 * The following .stab info is generated for "foo_type" and "foo" (this can
 * be seen by running "nm -pa" on the executable file generated by the
 * compiler.  The following is a truncated list.)
 *
 * 00410410 - 00 0000    SO t3.c
 * 00000000 - 00 0000  LSYM int:t1=r1;-2147483648;2147483647;
 * 00000000 - 00 0000  LSYM char:t2=r2;0;127;
 * 00000000 - 00 0000  LSYM long:t3=r1;-2147483648;2147483647;
 * 00000000 - 00 0000  LSYM short:t4=r1;-32768;32767;
 * 00000000 - 00 0000  LSYM unsigned char:t5=r1;0;255;
 * 00000000 - 00 0000  LSYM unsigned short:t6=r1;0;65535;
 * 00000000 - 00 0000  LSYM unsigned long:t7=r1;0;-1;
 * 00000000 - 00 0000  LSYM unsigned int:t8=r1;0;-1;
 * 00000000 - 00 0000  LSYM float:t9=r1;4;0;
 * 00000000 - 00 0000  LSYM double:t10=r1;8;0;
 * 00000000 - 00 0000  LSYM void:t11=11
 * 00000000 - 00 0000  LSYM ???:t12=1
 * 00000000 - 00 0048  LSYM foo_type:t13=s72array1:14=ar1;0;7;1,0,256;a:2,256,8;b:2,264,8;c:2,272,8;d:2,280,8;e:2,288,8;array2:15=ar1;0;7;1,320,256;;
 * 00000000 - 00 0048  GSYM foo:G13
 * 00410410 - 00 0004   FUN main:F1
 * 00000060 - 00 0004  PSYM argc:p1
 * 00000064 - 00 0001  PSYM argv:p16=*17=*2
 * 00410410 - 00 000e SLINE 
 * 00410418 - 00 000f SLINE 
 * 00410434 - 00 0010 SLINE 
 * 00410218  t -lg
 *
 * The "foo_type" and "foo" stabs can be broken down as (read from
 * bottom to top):
 *
 * 00000000 - 00 0048  LSYM
   ^        ^ ^  ^     ^
   |        | |  |     |
   |        | |  |     - local symbol (from n_type field)
   |        | |  - n_desc field
   |        | - n_other field
   |        - says we have .stab info used by dbx
   - n_value field, which is the value of the symbol or its size if it's
     a common or stab offset.

 * foo_type:t13=s72
   ^        ^^ ^^^
   |        || |||
   |        || ||- size of record is 72 bytes
   |        || |- there's a record being constructed
   |        || - type definition to follow
   |        |- number associated with this new type
   |        - says this is the creation of a new type
   - name of symbol

 *   array1:14=ar1;0;7;1,0,256;
     ^      ^ ^^^^ ^ ^ ^ ^ ^
     |      | |||| | | | | |
     |      | |||| | | | | - length (in bits) of this field
     |      | |||| | | | - bit offset of this field in the record
     |      | |||| | | - the array type is type 1 (int)
     |      | |||| | - upper bound
     |      | |||| - lower bound
     |      | |||- the subscript type is type 1 (int)
     |      | ||- it has a subscript
     |      | |- this is an array
     |      | - type definition to follow
     |      - the type of this field is type 14
     - the name of this field in the record

 *   a:2,256,8;
     ^ ^ ^   ^
     | | |   |
     | | |   - length (in bits) of this field
     | | - bit offset of this field in the record
     | - type associated with this field is type 2 (char)
     - name of this field in the record
 *
 * (the next 5 elements of the record are just variations of the first 2...)
 *
 *   b:2,264,8;
 *   c:2,272,8;
 *   d:2,280,8;
 *   e:2,288,8;
 *   array2:15=ar1;0;7;1,320,256;;
 *
 * 00000000 - 00 0048  GSYM
   ^        ^ ^  ^     ^
   |        | |  |     |
   |        | |  |     - global symbol (from n_type field)
   |        | |  - n_desc field
   |        | - n_other field
   |        - says we have .stab info used by dbx
   - n_value field, which is the value of the symbol or its size if it's
     a common or stab offset.
 * foo:G13
   ^   ^^
   |   ||
   |   |- type of this symbol is 13 (foo_type)
   |   - this symbol is an external variable
   - name of symbol
 *
 */

/*
 * Question:
 * While I'm on the subject, I find that a lot of the time I just want
 * to see array1[10] to array1[15].  Short of either typeing out
 * print commands for each of these fields, or typeing out the entire
 * array, is there a way to just print part of a large array from dbx with
 * one print command?  Thanks.
 *
 * Answer:
 * Aliases come in handy for these problems.  You could do several
 * things here:
 * (1) alias foo 'print foo.array1[10], foo.array1[11], ..., foo.array1[15]'
 *       You could add this alias to your .dbxinit file and have it
 *       get initialized every time you enter dbx.  This will give
 *       you all the elements of the array you specify.
 *
 * (2) alias foo  'foo0 ; foo3 ; foo6'
 *     alias foo0 'print foo.array1[0], foo.array1[1], foo.array1[2]'
 *     alias foo3 'print foo.array1[3], foo.array1[4], foo.array1[5]'
 *     alias foo6 'print foo.array1[6], foo.array1[7]'
 *       Same thing but with different granularity.
 *
 * (3) alias foo(x) 'print foo.array1[x]'
 *       This is better when you're looking at different elements
 *       that may be scattered throughout the array.  To get foo.array1[2],
 *       just say "foo(2)".
 *
 * We've also been thinking of making an enhancement to allow you
 * to specify "foo.array1[0..4]".  However, it has to wait in the
 * enhancement queue, which follows closely behind the problem
 * queue.  (Whatever happened to "it's the thought that counts"...)
 *
 * Gerry Cullen
 * gcullen@midas
 * Gould Computer Systems, Inc.
 * Ft. Lauderdale, Florida
 */