This patch steals an idea from Apple's gdb fork, namely "watch -location".
I wrote this from scratch but in the end it looks pretty similar to what
they did.
In my experience, I generally don't want gdb's scope-tracking logic for
watchpoint expressions. Instead, I'm usually just interested in some
bit of memory. I find myself typing this a lot:
print &expr
watch *$
This patch adds an option to "watch" to let me do this more directly.
(FWIW, this is a frequently-asked question on #gdb.)
I did not add an MI option for this (something Apple did do).
It didn't seem necessary to me.
I also didn't add Python API for this. I'm on the fence about whether
it is needed.
A doc review is needed, and of course I'd appreciate other comments.
Built and regtested on x86-64 (compile farm).
New tests included.
Tom
b/gdb/ChangeLog:
2010-08-11 Tom Tromey <tromey@redhat.com>
* breakpoint.c (watch_command_1): Add 'just_location' argument.
(watch_command_wrapper): Update.
(watch_maybe_just_location): New function.
(watch_command): Update.
(rwatch_command_wrapper): Update.
(rwatch_command): Update.
(awatch_command_wrapper): Update.
(awatch_command): Update.
b/gdb/doc/ChangeLog:
2010-08-11 Tom Tromey <tromey@redhat.com>
* gdb.texinfo (Set Watchpoints): Document -location option.
b/gdb/testsuite/ChangeLog:
2010-08-11 Tom Tromey <tromey@redhat.com>
* gdb.base/watchpoint.exp (test_watchpoint_and_breakpoint): Delete
watchpoint.
(test_watch_location): New proc.
(test_watchpoint_in_big_blob): Delete watchpoint.
* gdb.base/watchpoint.c (func5): New function.
(main): Call it.
diff --git a/gdb/breakpoint.c b/gdb/breakpoint.c
index 4affe0a..11c88b6 100644
--- a/gdb/breakpoint.c
+++ b/gdb/breakpoint.c
@@ -98,8 +98,6 @@ static void clear_command (char *, int);
static void catch_command (char *, int);
-static void watch_command (char *, int);
-
static int can_use_hardware_watchpoint (struct value *);
static void break_command_1 (char *, int, int);
@@ -173,12 +171,6 @@ static void hbreak_command (char *, int);
static void thbreak_command (char *, int);
-static void watch_command_1 (char *, int, int);
-
-static void rwatch_command (char *, int);
-
-static void awatch_command (char *, int);
-
static void do_enable_breakpoint (struct breakpoint *, enum bpdisp);
static void stop_command (char *arg, int from_tty);
@@ -7981,7 +7973,7 @@ watchpoint_exp_is_const (const struct expression *exp)
hw_read: watch read,
hw_access: watch access (read or write) */
static void
-watch_command_1 (char *arg, int accessflag, int from_tty)
+watch_command_1 (char *arg, int accessflag, int from_tty, int just_location)
{
struct breakpoint *b, *scope_breakpoint = NULL;
struct expression *exp;
@@ -8086,7 +8078,15 @@ watch_command_1 (char *arg, int accessflag, int from_tty)
exp_valid_block = innermost_block;
mark = value_mark ();
fetch_subexp_value (exp, &pc, &val, NULL, NULL);
- if (val != NULL)
+
+ if (just_location)
+ {
+ exp_valid_block = NULL;
+ val = value_addr (val);
+ release_value (val);
+ value_free_to_mark (mark);
+ }
+ else if (val != NULL)
release_value (val);
tok = arg;
@@ -8188,7 +8188,24 @@ watch_command_1 (char *arg, int accessflag, int from_tty)
b->exp = exp;
b->exp_valid_block = exp_valid_block;
b->cond_exp_valid_block = cond_exp_valid_block;
- b->exp_string = savestring (exp_start, exp_end - exp_start);
+ if (just_location)
+ {
+ struct type *t = value_type (val);
+ CORE_ADDR addr = value_as_address (val);
+ char *name;
+
+ t = check_typedef (TYPE_TARGET_TYPE (check_typedef (t)));
+ name = type_to_string (t);
+
+ b->exp_string = xstrprintf ("* (%s *) %s", name,
+ core_addr_to_string (addr));
+ xfree (name);
+
+ /* The above expression is in C. */
+ b->language = language_c;
+ }
+ else
+ b->exp_string = savestring (exp_start, exp_end - exp_start);
b->val = val;
b->val_valid = 1;
if (cond_start)
@@ -8215,7 +8232,8 @@ watch_command_1 (char *arg, int accessflag, int from_tty)
scope_breakpoint->related_breakpoint = b;
}
- value_free_to_mark (mark);
+ if (!just_location)
+ value_free_to_mark (mark);
/* Finally update the new watchpoint. This creates the locations
that should be inserted. */
@@ -8305,37 +8323,59 @@ can_use_hardware_watchpoint (struct value *v)
void
watch_command_wrapper (char *arg, int from_tty)
{
- watch_command (arg, from_tty);
+ watch_command_1 (arg, hw_write, from_tty, 0);
+}
+
+/* A helper function that looks for the "-location" argument and then
+ calls watch_command_1. */
+
+static void
+watch_maybe_just_location (char *arg, int accessflag, int from_tty)
+{
+ int just_location = 0;
+ if (strncmp (arg, "-location", sizeof ("-location") - 1) == 0)
+ {
+ arg += sizeof ("-location") - 1;
+ /* Handle "watch -location" as if there were an expression, and
+ let watch_command_1 issue an error. */
+ if (*arg == '\0' || isspace (*arg))
+ {
+ ep_skip_leading_whitespace (&arg);
+ just_location = 1;
+ }
+ }
+
+ watch_command_1 (arg, accessflag, from_tty, just_location);
}
static void
watch_command (char *arg, int from_tty)
{
- watch_command_1 (arg, hw_write, from_tty);
+ watch_maybe_just_location (arg, hw_write, from_tty);
}
void
rwatch_command_wrapper (char *arg, int from_tty)
{
- rwatch_command (arg, from_tty);
+ watch_command_1 (arg, hw_read, from_tty, 0);
}
static void
rwatch_command (char *arg, int from_tty)
{
- watch_command_1 (arg, hw_read, from_tty);
+ watch_maybe_just_location (arg, hw_read, from_tty);
}
void
awatch_command_wrapper (char *arg, int from_tty)
{
- awatch_command (arg, from_tty);
+ watch_command_1 (arg, hw_access, from_tty, 0);
}
static void
awatch_command (char *arg, int from_tty)
{
- watch_command_1 (arg, hw_access, from_tty);
+ watch_maybe_just_location (arg, hw_access, from_tty);
}
diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo
index 7abb9ed..5d2815f 100644
--- a/gdb/doc/gdb.texinfo
+++ b/gdb/doc/gdb.texinfo
@@ -3699,7 +3699,7 @@ watchpoints, which do not slow down the running of your program.
@table @code
@kindex watch
-@item watch @var{expr} @r{[}thread @var{threadnum}@r{]}
+@item watch @r{[}-location@r{]} @var{expr} @r{[}thread @var{threadnum}@r{]}
Set a watchpoint for an expression. @value{GDBN} will break when the
expression @var{expr} is written into by the program and its value
changes. The simplest (and the most popular) use of this command is
@@ -3716,13 +3716,20 @@ change the value of @var{expr}, @value{GDBN} will not break. Note
that watchpoints restricted to a single thread in this way only work
with Hardware Watchpoints.
+Ordinarily a watchpoint respects the scope of variables in @var{expr}
+(see below). The @code{-location} argument tells @value{GDBN} to
+instead watch the memory referred to by @var{expr}. In this case,
+@value{GDBN} will evaluate @var{expr}, take the address of the result,
+and watch that memory. If the expression's result does not have an
+address, then @value{GDBN} will print an error.
+
@kindex rwatch
-@item rwatch @var{expr} @r{[}thread @var{threadnum}@r{]}
+@item rwatch @r{[}-location@r{]} @var{expr} @r{[}thread @var{threadnum}@r{]}
Set a watchpoint that will break when the value of @var{expr} is read
by the program.
@kindex awatch
-@item awatch @var{expr} @r{[}thread @var{threadnum}@r{]}
+@item awatch @r{[}-location@r{]} @var{expr} @r{[}thread @var{threadnum}@r{]}
Set a watchpoint that will break when @var{expr} is either read from
or written into by the program.
diff --git a/gdb/testsuite/gdb.base/watchpoint.c b/gdb/testsuite/gdb.base/watchpoint.c
index 8c212c1..9ef9253 100644
--- a/gdb/testsuite/gdb.base/watchpoint.c
+++ b/gdb/testsuite/gdb.base/watchpoint.c
@@ -126,6 +126,17 @@ func4 ()
global_ptr++;
}
+void
+func5 ()
+{
+ int val = 0, val2 = 23;
+ int *x = &val;
+
+ /* func5 breakpoint here */
+ x = &val2;
+ val = 27;
+}
+
int main ()
{
#ifdef usestubs
@@ -203,5 +214,7 @@ int main ()
func4 ();
+ func5 ();
+
return 0;
}
diff --git a/gdb/testsuite/gdb.base/watchpoint.exp b/gdb/testsuite/gdb.base/watchpoint.exp
index 6029b5b..edc7ea0 100644
--- a/gdb/testsuite/gdb.base/watchpoint.exp
+++ b/gdb/testsuite/gdb.base/watchpoint.exp
@@ -615,6 +615,8 @@ proc test_watchpoint_and_breakpoint {} {
kfail "gdb/38" "next after watch x"
}
}
+
+ gdb_test_no_output "delete \$bpnum" "delete watch x"
}
}
@@ -628,6 +630,19 @@ proc test_constant_watchpoint {} {
gdb_test_no_output "delete \$bpnum" "delete watchpoint `7 + count'"
}
+proc test_watch_location {} {
+ gdb_breakpoint [gdb_get_line_number "func5 breakpoint here"]
+ gdb_continue_to_breakpoint "func5 breakpoint here"
+
+ gdb_test "watch -location *x" "atchpoint .*: .*" "watch -location .x"
+
+ gdb_test "continue" \
+ "Continuing.*\[Ww\]atchpoint .*: .*New value = 27.*" \
+ "continue with watch -location"
+
+ gdb_test_no_output "delete \$bpnum" "delete watch -location"
+}
+
proc test_inaccessible_watchpoint {} {
global gdb_prompt
@@ -678,6 +693,8 @@ proc test_watchpoint_in_big_blob {} {
gdb_test "watch buf" ".*atchpoint \[0-9\]+: buf"
gdb_test "cont" "Continuing.*atchpoint \[0-9\]+: buf\r\n\r\nOld value = .*testte\".*" "watchpoint on buf hit"
+
+ gdb_test_no_output "delete \$bpnum" "delete watch buf"
}
# Start with a fresh gdb.
@@ -853,6 +870,8 @@ if [initialize] then {
}
test_constant_watchpoint
+
+ test_watch_location
}
# Restore old timeout