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

Thiago Jung Bauermann
2009-12-23T23:43:39Z

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Hi,

This is a resubmission of a patch I posted long ago:

http://sourceware.org/ml/gdb-patches/2009-05/msg00670.html

It's good on its own, but is also important for ranged watchpoints in our
ppc476 support patches. Here's my original explanation:

Right now, GDB calls value_equal when comparing the old and new values
of a watchpoint. IMO this is not correct, since that function will call
coerce_array and effectively just compare the addresses of arrays being
watched.

This patch introduces a new value comparison function which works in the
mentioned case, and a testcase which fails without the patch and passes
with it.

Tromey had approved it here:

http://sourceware.org/ml/gdb-patches/2009-06/msg00076.html

But I don't know if approvals expire or not, so...

This version addresses Tromey's comments.
--
[]'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 2009-12-23 17:39:55.000000000 -0200
+++ gdb/gdb/breakpoint.c 2009-12-23 17:56:27.000000000 -0200
@@ -3174,7 +3174,6 @@ watchpoints_triggered (struct target_wai
#define BP_TEMPFLAG 1
#define BP_HARDWAREFLAG 2

-/* Check watchpoint condition. */

static int
watchpoint_check (void *p)
@@ -3245,8 +3244,12 @@ 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 2009-12-23 17:39:55.000000000 -0200
+++ gdb/gdb/testsuite/gdb.base/watchpoint.c 2009-12-23 17:40:03.000000000 -0200
@@ -30,7 +30,7 @@ int ival2 = -1;
int ival3 = -1;
int ival4 = -1;
int ival5 = -1;
-char buf[10];
+char buf[30];
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 2009-12-23 17:39:55.000000000 -0200
+++ gdb/gdb/testsuite/gdb.base/watchpoint.exp 2009-12-23 17:40:03.000000000 -0200
@@ -678,6 +678,24 @@ proc test_inaccessible_watchpoint {} {
}
}

+proc test_watchpoint_in_big_blob {} {
+ global gdb_prompt
+
+ gdb_test "watch buf" ".*atchpoint \[0-9\]+: buf"
+ send_gdb "cont\n"
+ gdb_expect {
+ -re "Continuing.*\[Ww\]atchpoint.*buf.*Old value = .*$gdb_prompt $" {
+ pass "watchpoint on buf hit"
+ }
+ -re "Continuing.*$gdb_prompt $" {
+ fail "watchpoint on buf hit"
+ }
+ -re ".*$gdb_prompt $" { fail "watchpoint on buf hit" ; return }
+ timeout { fail "watchpoint on buf hit (timeout)" ; return }
+ eof { fail "watchpoint on buf hit (eof)" ; return }
+ }
+}
+
# Start with a fresh gdb.

gdb_exit
@@ -842,6 +860,8 @@ 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 2009-12-23 17:44:23.000000000 -0200
+++ gdb/gdb/valarith.c 2009-12-23 17:53:15.000000000 -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 2009-12-23 17:53:47.000000000 -0200
+++ gdb/gdb/value.h 2009-12-23 17:58:36.000000000 -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);