Re: [RFA] Fix verification of changed values for big values.

[Thiago Jung Bauermann <bauerman@br.ibm.com>]

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On Thu 24 Dec 2009 02:41:25 Joel Brobecker wrote:
> > gdb/
> > 	* valarith.c (value_equal_contents): New function.
> > 	* value.h (value_equal_contents): Declare.
> > 	* breakpoint.c (watchpoint_check): Use value_equal_contents
> > 	instead of value_equal.
> 
> OK, with just one little request.

Thanks!

> > -/* Check watchpoint condition.  */
> >
> >  static int
> >  watchpoint_check (void *p)
> 
> Can you add a short description of what the function does? We would
> like all functions to be documented...  In particular, since P is
> declared as a void *, it's probably going to be useful to explain
> what the real type is supposed to be.

The purpose of the function is rather simple, so I didn't have much to say.
I added this description:

/* Evaluate watchpoint condition expression and check if its value changed.  */

> > +/* Compare values based on their raw contents. Useful for arrays since
> 
>                                                  ^ Missing space

Fixed.

> > +    send_gdb "cont\n"
> > +    gdb_expect {
> > +	-re "Continuing.*\[Ww\]atchpoint.*buf.*Old value = .*$gdb_prompt $" {
> > +	    pass "watchpoint on buf hit"
> > +	}
> 
> I am wondering if this could be written more simply, by using gdb_test?
> 
> gdb_test "cont" "Continuing.*\[Ww\]atchpoint.*buf.*Old value = .*" [...]
> 
> ? Otherwise, we try to avoid the use of send_gdb/gdb_expect, as it
> forces you to handle by hand all possible failure conditions. You can

You're right. IIRC I used gdb_expect because I wanted to explicitly check
for the gdb prompt in my regex, to avoid it being too greedy. But I changed
the testcase a little bit and now I don't need that anymore.

This is what I committed.
-- 
[]'s
Thiago Jung Bauermann
IBM Linux Technology Center


gdb/
	* valarith.c (value_equal_contents): New function.
	* value.h (value_equal_contents): Declare.
	* breakpoint.c (watchpoint_check): Use value_equal_contents
	instead of value_equal.

gdb/testsuite/
	* gdb.base/watchpoint.exp (test_watchpoint_in_big_blob): New function.
	(top level): Call test_watchpoint_in_big_blob.
	* gdb.base/watchpoint.c (buf): Change size to value too big for hardware
	watchpoints.
	(func3): Write to buf.

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Index: gdb/gdb/breakpoint.c
===================================================================
--- gdb.orig/gdb/breakpoint.c	2009-12-28 10:10:40.000000000 -0200
+++ gdb/gdb/breakpoint.c	2009-12-28 11:46:36.000000000 -0200
@@ -3174,7 +3174,7 @@ watchpoints_triggered (struct target_wai
 #define BP_TEMPFLAG 1
 #define BP_HARDWAREFLAG 2
 
-/* Check watchpoint condition.  */
+/* Evaluate watchpoint condition expression and check if its value changed.  */
 
 static int
 watchpoint_check (void *p)
@@ -3245,8 +3245,12 @@ watchpoint_check (void *p)
       struct value *new_val;
 
       fetch_watchpoint_value (b->exp, &new_val, NULL, NULL);
+
+      /* We use value_equal_contents instead of value_equal because the latter
+	 coerces an array to a pointer, thus comparing just the address of the
+	 array instead of its contents.  This is not what we want.  */
       if ((b->val != NULL) != (new_val != NULL)
-	  || (b->val != NULL && !value_equal (b->val, new_val)))
+	  || (b->val != NULL && !value_equal_contents (b->val, new_val)))
 	{
 	  if (new_val != NULL)
 	    {
Index: gdb/gdb/testsuite/gdb.base/watchpoint.c
===================================================================
--- gdb.orig/gdb/testsuite/gdb.base/watchpoint.c	2009-12-28 10:10:40.000000000 -0200
+++ gdb/gdb/testsuite/gdb.base/watchpoint.c	2009-12-28 11:32:04.000000000 -0200
@@ -30,7 +30,7 @@ int ival2 = -1;
 int ival3 = -1;
 int ival4 = -1;
 int ival5 = -1;
-char buf[10];
+char buf[30] = "testtesttesttesttesttesttestte";
 struct foo
 {
   int val;
@@ -95,6 +95,7 @@ func3 ()
   x = 1;				/* second x assignment */
   y = 1;
   y = 2;
+  buf[26] = 3;
 }
 
 int
Index: gdb/gdb/testsuite/gdb.base/watchpoint.exp
===================================================================
--- gdb.orig/gdb/testsuite/gdb.base/watchpoint.exp	2009-12-28 10:10:40.000000000 -0200
+++ gdb/gdb/testsuite/gdb.base/watchpoint.exp	2009-12-28 11:46:01.000000000 -0200
@@ -678,6 +678,13 @@ proc test_inaccessible_watchpoint {} {
     }
 }
     
+proc test_watchpoint_in_big_blob {} {
+    global gdb_prompt
+
+    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"
+}
+
 # Start with a fresh gdb.
 
 gdb_exit
@@ -842,6 +849,8 @@ if [initialize] then {
     }
 
     test_watchpoint_and_breakpoint
+
+    test_watchpoint_in_big_blob
 }
 
 # Restore old timeout
Index: gdb/gdb/valarith.c
===================================================================
--- gdb.orig/gdb/valarith.c	2009-12-28 10:10:40.000000000 -0200
+++ gdb/gdb/valarith.c	2009-12-28 11:47:45.000000000 -0200
@@ -1397,6 +1397,24 @@ value_equal (struct value *arg1, struct 
     }
 }
 
+/* Compare values based on their raw contents.  Useful for arrays since
+   value_equal coerces them to pointers, thus comparing just the address
+   of the array instead of its contents.  */
+
+int
+value_equal_contents (struct value *arg1, struct value *arg2)
+{
+  struct type *type1, *type2;
+
+  type1 = check_typedef (value_type (arg1));
+  type2 = check_typedef (value_type (arg2));
+
+  return (TYPE_CODE (type1) == TYPE_CODE (type2)
+	  && TYPE_LENGTH (type1) == TYPE_LENGTH (type2)
+	  && memcmp (value_contents (arg1), value_contents (arg2),
+		     TYPE_LENGTH (type1)) == 0);
+}
+
 /* Simulate the C operator < by returning 1
    iff ARG1's contents are less than ARG2's.  */
 
Index: gdb/gdb/value.h
===================================================================
--- gdb.orig/gdb/value.h	2009-12-28 10:10:40.000000000 -0200
+++ gdb/gdb/value.h	2009-12-28 10:10:56.000000000 -0200
@@ -563,6 +563,8 @@ extern struct internalvar *lookup_intern
 
 extern int value_equal (struct value *arg1, struct value *arg2);
 
+extern int value_equal_contents (struct value *arg1, struct value *arg2);
+
 extern int value_less (struct value *arg1, struct value *arg2);
 
 extern int value_logical_not (struct value *arg1);