Sven Rudolph writes in email to me:
> > Package: gdb
> > Version: 4.12
> >
> > As you can see below, when setting a memory breakpoint on a structure
> > member GDB uses the address of the start of the structure by mistake.
> > Applying *& to the member (to take its address and then dereference
> > it) gives correct results.
>
> (typescript deleted)
>
> You used commands that don't even exist in the current version of gdb,
> so i cannot reproduce this problem. I'm not a gdb expert, so please
> try to reproduce this problem on a current gdb (or close the bug) .
These commands have equivalents in gdb 4.14-1. However, the
equivalents don't appear to work for me at all. See the transcript
below.
Please can we keep this bug open until (a) the memory watchpoints,
which are a useful feature, work and (b) we see that the original bug
is fixed.
Ian.
-chiark:~/junk> cat t.c
struct foo { int a,b; };
void fong(struct foo *p, int x) { p->b=x; }
int main(int argc, char **argv) {
struct foo f;
f.a= 2;
f.b= 3;
fong(&f,4);
f.b=5;
fong(&f,6);
}
-chiark:~/junk> gcc -g t.c
-chiark:~/junk> gdb a.out
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 4.14 (i486-debian-linux), Copyright 1995 Free Software Foundation, Inc...
(gdb) break main
Breakpoint 1 at 0x1093: file t.c, line 7.
(gdb) run
Starting program: /u/ian/junk/a.out
Breakpoint 1, main (argc=1, argv=0xbffff858) at t.c:7
7 f.a= 2;
(gdb) step
8 f.b= 3;
(gdb) step
9 fong(&f,4);
(gdb) print f
$1 = {a = 2, b = 3}
(gdb) watch f.b
Hardware watchpoint 2: f.b
(gdb) watch f.a
Hardware watchpoint 3: f.a
(gdb) watch *&f.b
Hardware watchpoint 4: *&f.b
(gdb) info watchpoints
Num Type Disp Enb Address What
1 breakpoint keep y 0x00001093 in main at t.c:7
breakpoint already hit 1 time
2 hw watchpoint keep y f.b
3 hw watchpoint keep y f.a
4 hw watchpoint keep y *&f.b
(gdb) cont
Continuing.
warning: Hardware watchpoint 3: Could not insert watchpoint
warning: Hardware watchpoint 4: Could not insert watchpoint
ptrace: Unknown error -1.
Cannot insert breakpoints.
The same program may be running in another process.
(gdb) quit
The program is running. Quit anyway (and kill it)? (y or n) y
-chiark:~/junk>
