[Bug python/13111] New: "-var-update" command incorrect when using pretty printers
developer at audioranger dot com
sourceware-bugzilla@sourceware.org
Fri Aug 19 15:46:00 GMT 2011
http://sourceware.org/bugzilla/show_bug.cgi?id=13111
Bug #: 13111
Summary: "-var-update" command incorrect when using pretty
printers
Product: gdb
Version: 7.3
Status: NEW
Severity: minor
Priority: P2
Component: python
AssignedTo: unassigned@sourceware.org
ReportedBy: developer@audioranger.com
Classification: Unclassified
The gdb/mi command "-var-update" may return an incorrect value for
"type_changed" when pretty-printers are used.
Consider the following example. The struct "printMePretty" should be
pretty-printed by using the Python TestPrinter class from below. It should be
printed as an integer "array" (it doesn't actually makes sense here, it's just
for testing) if the structure's "printAsInt" member is true, and as a floating
point "array" otherwise.
****************** File: main.cpp *****************
struct printMePretty
{
bool printAsInt;
int intMember;
float floatMember;
printMePretty() :
printAsInt(true),
intMember(0xFF),
floatMember(3.1415)
{ }
};
void main()
{
printMePretty pretty;
pretty.printAsInt = false;
}
****************** File: printer.py *****************
[...]
class TestPrinter:
class _iterator:
def __init__(self, val):
self.val = val
self.index = 0
def __iter__(self):
return self
def next(self):
if self.index == 1:
raise StopIteration
if self.val['printAsInt']:
childValue = self.val['intMember']
else:
childValue = self.val['floatMember']
self.index += 1
return ('Value', childValue)
def __init__(self, val):
self.val = val
def children(self):
return self._iterator(self.val)
def display_hint(self):
return 'array'
****************** End of file *****************
Using Eclipse CDT to trace gdb/mi commands, one encounters the following until
the line "pretty.printAsInt = false;":
-var-create --thread 1 --frame 0 - * pretty
^done,name="var1",numchild="0",value="{...}",type="printMePretty",thread-id="1",displayhint="array",dynamic="1",has_more="1"
-var-list-children var1 0 1
^done,numchild="1",displayhint="array",children=[child={name="var1.Value",exp="Value",numchild="0",type="int",thread-id="1"}],has_more="0"
OK, so "var1.Value" has type "int". Now, stepping over the line
"pretty.printAsInt = false;" results in:
-var-update 1 var1
^done,changelist=[{name="var1.Value",value="3.1415",in_scope="true",type_changed="false",displayhint="array",dynamic="1",has_more="0"}]
It now says that "var1.Value" would have a "value" of "3.1415" - that's
obviously a strange value for an "int" (since "type_changed" reports "false" -
I suppose it should actually report that the type has changed to "float").
This seems like a bug within gdb to me. The same problem may also apply if a
pretty-printer's toString() method returns gdb.Values which have different
gdb.Types, depending on the data members of the structure which should be
pretty-printed.
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