Re: Robustifying pretty-printers

Phil Muldoon
2009-06-15T12:28:51Z

> In fact, there's yet another case:
>
> class StdStringPrinter:
> "Print a std::basic_string of some kind"
>
> def __init__(self, encoding, val):
> self.encoding = encoding
> self.val = val
>
> def to_string(self):
> # Look up the target encoding as late as possible.
> encoding = self.encoding
> if encoding == 0:
> encoding = gdb.parameter('target-charset')
> elif encoding == 1:
> encoding = gdb.parameter('target-wide-charset')
> elif isinstance(encoding, WideEncoding):
> encoding = encoding.value
> return self.val['_M_dataplus']['_M_p'].string(encoding)
>
> I am not quite sure where the 'string' method is defined, so the
> question is -- assuming I know the expected size of the string.
> How do I make the 'string' method not to fetch more than that?
>

I'll answer a particular question in your email: counted string support
should hopefully arrive soon. This comprises of two patches currently
working through the review process over on the archer mailing list.

The approved first part is here:

http://sourceware.org/ml/archer/2009-q2/msg00017.html

The second part is more to do with null character preservation and
emission, but has some counted string dependencies. It is currently
going through review here:

http://sourceware.org/ml/archer/2009-q2/msg00111.html

When these have been accepted there, I'll submit them to the gdb-patches
for additional review, and then hopefully into GDB head pretty soon.

In the std:string example, it would be modified to use counted strings
like so:

diff --git a/gdb/python/lib/gdb/libstdcxx/v6/printers.py
b/gdb/python/lib/gdb/libstdcxx/v6/printers.py
index 2bd2593..6bf4f3b 100644
--- a/gdb/python/lib/gdb/libstdcxx/v6/printers.py
+++ b/gdb/python/lib/gdb/libstdcxx/v6/printers.py
@@ -468,7 +468,17 @@ class StdStringPrinter:
encoding = gdb.parameter('target-charset')
elif isinstance(encoding, WideEncoding):
encoding = encoding.value
- return self.val['_M_dataplus']['_M_p'].string(encoding)
+ type = self.val.type
+ if type.code == gdb.TYPE_CODE_REF:
+ type = type.target ()
+
+ ptr = self.val ['_M_dataplus']['_M_p']
+ realtype = type.unqualified ().strip_typedefs ()
+ reptype = gdb.lookup_type (str (realtype) + '::_Rep').pointer ()
+ header = ptr.cast(reptype) - 1
+ len = header.dereference ()['_M_length']
+
+ return self.val['_M_dataplus']['_M_p'].string (encoding, length = len)

But the optional string length parameter could be used in other
examples, too.

Regards

Phil