🚀 go-pugleaf

I have run into a bug in GDB 4.5 on a Decstation 5000/20 running Mach
3.0 (MK77 + UX39).  It is not able to print structs that contain a
void pointer as the first field.  Also, ptype does not print the type
definition correctly.  The 'bug' exists in both a locally modified
version built using a 'Mach configuration' and in a version that I
believe was built using GCC 2.1/2.2 and the distributed 'decstation'
configuration.  I used the latter version to produce the log included
below.

I have enclosed a sample program and a log of GDB session that
demonstrate the bug.  The sample program was compiled with GCC 2.3.2 and
the following command: gcc -ansi -Wall -g -o foo foo.c

I have also enclosed a partial dump of the program's symbol table.

I suspect that GDB is guessing that a struct with a void * as the first
member is an 'enum' rather than 'struct'.  This is based on the code in
parse_symbol in the file gdb/mipsread.c.  Here is the code fragment from
mipsread.c for GDB versions 4.5.

                    /* First count the number of fields. */
                    for (tsym = sh+1; tsym->st != stEnd; tsym++)
                        if (tsym->st == stMember) {
                            if (nfields == 0 && type_code == TYPE_CODE_UNDEF)
                                /* If the type of the member is Nil (or Void)
                                   assume the tag is an enumeration. */
                                if (tsym->index == indexNil)
                                    type_code = TYPE_CODE_ENUM;
                                else {
                                    ecoff_swap_tir_in (bigend,
                                                       &ax[tsym->index].a_ti,
                                                       &tir);
                                    if (tir.bt == btNil || tir.bt == btVoid)
                                        type_code = TYPE_CODE_ENUM;
                                }
                            nfields++;
                            if (tsym->value > max_value)
                                max_value = tsym->value;
                        }

After calling ecoff_swap_tir_in it checks whether the base type of the file
is btNil.  The nm-dump reports the void pointer fields as 'btNil *'.  Should
the code in parse_symbol be checking for a type qualifier?

If I have correctly figured out the problem, it still exists in version 4.7.

					Peter Stout
					(pds@cs.cmu.edu)

----- Begin Program
typedef struct queue {
	void *p1;
	void *p2;
} queue_t;

typedef struct _foo {
	char *p1;
	void *p2;
} foo_t;

typedef struct _bar {
	void *p1;
	char *p2;
} bar_t;

typedef struct _baz {
	char *p1;
	char *p2;
} baz_t;

void main(int argc, char **argv)
{
    extern volatile void exit(int);
    queue_t	q;
    foo_t	foo;
    bar_t	bar;
    baz_t	baz;
    char	temp[16] = "\001\002\004\010";

    q.p1 = temp;
    foo.p2 = &temp[1];
    bar.p1 = &temp[2];
    baz.p2 = &temp[3];

    exit(*(char *)q.p1 + *(char *)foo.p2 + *(char *)bar.p1 + *baz.p2);
}
----- End Program

----- Begin Log
pds:pds> /usr/misc/bin/gdb foo
GDB is free software and you are welcome to distribute copies of it
 under certain conditions; type "show copying" to see the conditions.
There is absolutely no warranty for GDB; type "show warranty" for details.
GDB 4.5, Copyright 1992 Free Software Foundation, Inc...
(gdb) ptype queue_t
type = struct queue {
    struct queue p1;
    struct queue p2;
}
(gdb) ptype foo
No symbol "foo" in current context.
(gdb) ptype foo_t
type = struct _foo {
    char *p1;
    void *p2;
}
(gdb) ptype bar_t
type = struct _bar {
    struct _bar p1;
    struct _bar p2;
}
(gdb) ptype baz_t
type = struct _baz {
    char *p1;
    char *p2;
}
(gdb) quit

If you attempt to print a variable of type queue_t or bar_t GDB goes
into (infinite) recursion until you type ^C.

----- End Log

----- Begin Symbol Table (nm -a -p foo)
Symbols from foo:

Name                  Value   Class        Type           Size  Indx  Section

../../../../../src/mk/user/libmach/mips/crt0.ss|00000000|File    |ref=7             |      |  0|Text    
__start             |00400140|Proc    |end=6 btNil       |      |  1|Text    
$32                 |00400194|Label   |                  |      |  2|Text    
$33                 |004001c0|Label   |                  |      |  3|Text    
$34                 |004001e4|Label   |                  |      |  4|Text    
__start             |000000bc|End     |ref=1             |      |  5|Text    
../../../../../src/mk/user/libmach/mips/crt0.ss|00000000|End     |ref=0             |      |  6|Text    
foo.c               |00000000|File    |ref=40            |      |  7|Text    
queue               |00000008|Block   |ref=12            |      |  8|Info    
p1                  |00000000|Member  |btNil *           |      |  9|Info    
p2                  |00000020|Member  |btNil *           |      | 10|Info    
                    |00000000|End     |ref=8             |      | 11|Info    
queue_t             |00000000|Typdef  |struct queue      |      | 12|Info    
_foo                |00000008|Block   |ref=17            |      | 13|Info    
p1                  |00000000|Member  |char *            |      | 14|Info    
p2                  |00000020|Member  |btNil *           |      | 15|Info    
                    |00000000|End     |ref=13            |      | 16|Info    
foo_t               |00000000|Typdef  |struct _foo       |      | 17|Info    
_bar                |00000008|Block   |ref=22            |      | 18|Info    
p1                  |00000000|Member  |btNil *           |      | 19|Info    
p2                  |00000020|Member  |char *            |      | 20|Info    
                    |00000000|End     |ref=18            |      | 21|Info    
bar_t               |00000000|Typdef  |struct _bar       |      | 22|Info    
_baz                |00000008|Block   |ref=27            |      | 23|Info    
p1                  |00000000|Member  |char *            |      | 24|Info    
p2                  |00000020|Member  |char *            |      | 25|Info    
                    |00000000|End     |ref=23            |      | 26|Info    
baz_t               |00000000|Typdef  |struct _baz       |      | 27|Info    
main                |00400200|Proc    |end=32 btNil      |      | 28|Text    
argc                |00000000|Param   |int               |      | 29|Abs     
argv                |00000004|Param   |char **           |      | 30|Abs     
                    |0000001c|Block   |ref=38            |      | 31|Text    
q                   |ffffffc8|Local   |struct queue      |      | 32|Abs     
foo                 |ffffffd0|Local   |struct _foo       |      | 33|Abs     
bar                 |ffffffd8|Local   |struct _bar       |      | 34|Abs     
baz                 |ffffffe0|Local   |struct _baz       |      | 35|Abs     
temp                |ffffffe8|Local   |char [16]         |      | 36|Abs     
                    |000000b4|End     |ref=31            |      | 37|Text    
main                |000000c8|End     |ref=28            |      | 38|Text    
foo.c               |00000000|End     |ref=7             |      | 39|Text    

symbols for libgcc and libc deleted.

----- End Symbol Table