Re: Checking if addess is on stack?

[Eli Zaretskii <eliz@gnu.org>]

> From: Vladimir Prus <ghost@cs.msu.su>
> Date: Thu, 20 Apr 2006 19:31:37 +0400
> Cc: gdb@sources.redhat.com
> 
> (gdb) watch *ptr
> Hardware watchpoint 2: *ptr
> (gdb) c
> Continuing.
> Hardware watchpoint 2 deleted because the program has left the block
> in which its expression is valid.
> 
> Program exited normally.
> (gdb)
> 
> I don't watch watchpoint 2 to be deleted in this case.

You could put 2 watchpoints instead of one, as in the session attached
at the end of this message.  (Yes, I know that it triggers outside
`main', but that's what we have now.)

> I want to set breakpoint at address, and be it automatically removed when 
> leaving function, if and only if the address is on function stack.

Doing this in all cases would be a misfeature, for the reasons I tried
to explain: users normally expect us to stop the program when any one
of the variables which contribute to an expression's value are
modified.

> In current gdb, I can either:
> 1. Set watchpoint on expression, and it will be always deleted, like in above 
> case.
> 2. Set watchpoint on address, and it won't be ever deleted.

I suggested a possible enhancement to watchpoints to do better, but
someone will have to code it (assuming that people agree with my
suggestion).


D:\usr\eli\data>gdb ./dbw.exe
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This GDB was configured as "i686-pc-mingw32"...
(gdb) b set
Breakpoint 1 at 0x401293: file dbw.c, line 3.
(gdb) r
Starting program: D:\usr\eli\data/./dbw.exe

Breakpoint 1, set (ptr=0x22ff74) at dbw.c:3
3           *ptr = 10;
(gdb) watch *ptr
Hardware watchpoint 2: *ptr
(gdb) p/x ptr
$1 = 0x22ff74
(gdb) watch *(int *)$1
Hardware watchpoint 3: *(int *) $1
(gdb) c
Continuing.
Hardware watchpoint 2: *ptr

Old value = 2
New value = 10
Hardware watchpoint 4: *(int *) $1

Old value = 2
New value = 10
set (ptr=0x22ff74) at dbw.c:4
4       }
(gdb) c
Continuing.

Watchpoint 2 deleted because the program has left the block in
which its expression is valid.
main () at dbw.c:15
15          modify(&i);
(gdb) c
Continuing.
Hardware watchpoint 4: *(int *) $1

Old value = 10
New value = 15
modify (ptr=0x22ff74) at dbw.c:9
9       }
(gdb) c
Continuing.
Hardware watchpoint 4: *(int *) $1

Old value = 15
New value = 0
0x77c39ebb in msvcrt!_cexit ()
(gdb) c
Continuing.
Hardware watchpoint 4: *(int *) $1

Old value = 0
New value = -1
0x7c81caa9 in KERNEL32!ExitProcess () from C:\WINDOWS\system32\kernel32.dll
(gdb) c
Continuing.

Program exited normally.
(gdb)