[Bug python/17728] New: gdb.LazyString is confused by typedefs

[jwakely.gcc at gmail dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=17728

Bug ID: 17728
Summary: gdb.LazyString is confused by typedefs
Product: gdb
Version: 7.8
Status: NEW
Severity: normal
Priority: P2
Component: python
Assignee: unassigned at sourceware dot org
Reporter: jwakely.gcc at gmail dot com

tmp$ cat > str.cc
struct Foo {
Foo() : str("foo"), len(3) { }
const char* str;
int len;
};

struct Bar {
Bar() : str("bar"), len(3) { }
typedef const char* pointer;
pointer str;
int len;
};

int main()
{
Foo foo;
Bar bar;
return 0;
}
tmp$ cat > a.out-gdb.py
import gdb

class StrPrinter:
"Print a stringy thingie"

def __init__ (self, val):
self.val = val

def to_string (self):
s = self.val['str']
l = self.val['len']
return s.lazy_string(length = l)

def display_hint(self):
return 'string'

def str_lookup_function(val):
lookup_tag = val.type.tag
if lookup_tag == "Foo" or lookup_tag == "Bar":
return StrPrinter(val)
return None

gdb.current_objfile().pretty_printers.append(str_lookup_function)
tmp$ g++ -g str.cc
tmp$ ~/gcc/gdb/7.8.50/bin/gdb
GNU gdb (GDB) 7.8.50.20141216-cvs
Copyright (C) 2014 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law. Type "show copying"
and "show warranty" for details.
This GDB was configured as "x86_64-unknown-linux-gnu".
Type "show configuration" for configuration details.
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>.
Find the GDB manual and other documentation resources online at:
<http://www.gnu.org/software/gdb/documentation/>.
For help, type "help".
Type "apropos word" to search for commands related to "word".
(gdb) set auto-load safe-path /
(gdb) file a.out
Reading symbols from a.out...done.
(gdb) start
Temporary breakpoint 1 at 0x4005b8: file str.cc, line 16.
Starting program: /tmp/a.out

Temporary breakpoint 1, main () at str.cc:16
16 Foo foo;
(gdb) n
17 Bar bar;
(gdb) p foo
$1 = "foo"
(gdb) n
18 return 0;
(gdb) p bar
$2 = "\x4006b4\003\000\000\000\000\000\000\000\x4006b0"
(gdb)

The LazyString seems to be confused by the fact that Bar::str is declared with
a typedef, so it prints the contents of &bar.str instead of bar.str

The only solution I've found is to strip the typedef first:

def to_string (self):
s = self.val['str']
s = s.cast(s.type.strip_typedefs())
l = self.val['len']
return s.lazy_string(length = l)

[jwakely.gcc at gmail dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=17728

--- Comment #1 from Jonathan Wakely <jwakely.gcc at gmail dot com> ---
This seems odd:

(gdb) python print StrPrinter(gdb.parse_and_eval('foo')).to_string().type
const char
(gdb) python print StrPrinter(gdb.parse_and_eval('bar')).to_string().type
Bar::pointer

https://sourceware.org/gdb/onlinedocs/gdb/Lazy-Strings-In-Python.html says type
"will always be a pointer type" but the lazy string for foo is not a pointer.
The lazy string for bar is a typedef for a pointer, but doesn't work correctly.

Also odd:

(gdb) python print StrPrinter(gdb.parse_and_eval('foo')).to_string().value()
102 'f'
(gdb) python print StrPrinter(gdb.parse_and_eval('bar')).to_string().value()
0x4006b4 "bar"

The LazyString.value() method shows the right thing for bar, but not for foo
(which is at least consistent with the .type attribute which says that foo's
type is just a char not a char*)

[cvs-commit at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=17728

--- Comment #2 from cvs-commit at gcc dot gnu.org <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Doug Evans <***@sourceware.org>:

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=34b433203b5f56149c27a8dfea21a921392cb158

commit 34b433203b5f56149c27a8dfea21a921392cb158
Author: Doug Evans <***@google.com>
Date: Wed Mar 15 15:35:13 2017 -0700

Fix various python lazy string bugs.

gdb/ChangeLog:

PR python/17728, python/18439, python/18779
* python/py-lazy-string.c (lazy_string_object): Clarify use of LENGTH
member. Change type of TYPE member to PyObject *. All uses updated.
(stpy_convert_to_value): Fix handling of TYPE_CODE_PTR.
(gdbpy_create_lazy_string_object): Flag bad length values.
Handle TYPE_CODE_ARRAY with possibly different user-provided length.
Handle typedefs in incoming type.
(stpy_lazy_string_elt_type): New function.
(gdbpy_extract_lazy_string): Call it.
* python/py-value.c (valpy_lazy_string): Flag bad length values.
Fix handling of TYPE_CODE_PTR. Handle TYPE_CODE_ARRAY. Handle
typedefs in incoming type.

gdb/testsuite/ChangeLog:

PR python/17728, python/18439, python/18779
* gdb.python/py-value.c (main) Delete locals sptr, sn.
* gdb.python/py-lazy-string.c (pointer): New typedef.
(main): New locals ptr, array, typedef_ptr.
* gdb.python/py-value.exp: Move lazy string tests to ...
* gdb.python/py-lazy-string.exp: ... here. Add more tests for pointer,
array, typedef lazy strings.

[pmuldoon at redhat dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=17728

Phil Muldoon <pmuldoon at redhat dot com> changed:

What |Removed |Added
----------------------------------------------------------------------------
Status|NEW |WAITING
CC| |pmuldoon at redhat dot com

--- Comment #3 from Phil Muldoon <pmuldoon at redhat dot com> ---
Can we close this bug, Doug?

[tromey at sourceware dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=17728

Tom Tromey <tromey at sourceware dot org> changed:

What |Removed |Added
----------------------------------------------------------------------------
Status|WAITING |RESOLVED
CC| |tromey at sourceware dot org
Resolution|--- |FIXED

--- Comment #4 from Tom Tromey <tromey at sourceware dot org> ---
I tried the original test case and it is fixed.