[Bug python/11417] New: lazy string of zero length requires a valid pointer

[Bug python/11417] New: lazy string of zero length requires a valid pointer

[zilla at kayari dot org]

I don't know if this behaviour is intentional, but it used to work when I was
using gdb.Value.string and fails with gdb.Value.lazy_string

I have a pretty printer for a string-like C++ class holding a char pointer and a
length.  The pointer can be NULL, in which case the length will be 0.

struct Str {
    Str(const char* s = 0) : str(s), len(s ? strlen(s) : 0) { }
    const char* str;
    int len;
};

Previously my pretty printer looked like:

class StrPrinter:
    "Print a Str"

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

    def to_string (self):
        return '"' + self.val['str'].string('', 'ignore', self.val['len']) + '"'

If the pointer was null this printed ""

(gdb) p/r null
$5 = {str = 0x0, len = 0}
(gdb) p null
$6 = ""

(this despite the docs for Value.string saying "The string is assumed to be
terminated by a zero of the appropriate width.")

I changed the printer to:

class Str2Printer:
    "Print a Str2"

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

    def to_string (self):
        return self.val['str'].lazy_string('', self.val['len'])

I like that I don't need to add double-quotes now, but it seems I now need to
handle NULL explicitly because lazy string doesn't like NULL even when the
length is zero:

(gdb) p/r null2
$2 = {str = 0x0, len = 0}
(gdb) p null2
$3 = Traceback (most recent call last):
  File "/home/wakelj/src/tests/pretty/str-gdb.py", line 23, in to_string
    return self.val['str'].lazy_string('', self.val['len'])
MemoryError: Cannot create a lazy string from a GDB-side string.

Are these differences between Value.string and Value.lazy_string intentional?

-- 
           Summary: lazy string of zero length requires a valid pointer
           Product: gdb
           Version: 7.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: python
        AssignedTo: unassigned at sourceware dot org
        ReportedBy: zilla at kayari dot org
                CC: gdb-prs at sourceware dot org


http://sourceware.org/bugzilla/show_bug.cgi?id=11417

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[Bug python/11417] lazy string of zero length requires a valid pointer

[pmuldoon at redhat dot com]

------- Additional Comments From pmuldoon at redhat dot com  2010-03-24 17:23 -------
This looks bogus. The lazy string code seems to be incorrectly identifying the
string as a GDB side string (ie not in the inferior, has no address in the
inferior and is stored in GDB).  Patch forthcoming.

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
         AssignedTo|unassigned at sourceware dot|pmuldoon at redhat dot com
                   |org                         |
             Status|UNCONFIRMED                 |ASSIGNED
     Ever Confirmed|                            |1


http://sourceware.org/bugzilla/show_bug.cgi?id=11417

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[Bug python/11417] lazy string of zero length requires a valid pointer

[pmuldoon at redhat dot com]

------- Additional Comments From cvs-commit at gcc dot gnu dot org  2010-04-08 10:28 -------
Subject: Bug 11417

CVSROOT:	/cvs/src
Module name:	src
Changes by:	pmuldoon@sourceware.org	2010-04-08 10:28:42

Modified files:
	gdb            : ChangeLog 
	gdb/python     : py-lazy-string.c 
	gdb/testsuite  : ChangeLog 
	gdb/testsuite/gdb.python: py-value.c py-value.exp 

Log message:
	2010-04-08  Phil Muldoon  <pmuldoon@redhat.com>
	
	PR python/11417
	
	* python/py-lazy-string.c (stpy_convert_to_value): Check for
	a NULL address.
	(gdbpy_create_lazy_string_object): Allow strings with a NULL
	address and a zero length.
	
	2010-04-08  Phil Muldoon  <pmuldoon@redhat.com>
	
	* gdb.python/py-value: Add null string variable.
	(test_lazy_string): Test zero length, NULL address lazy
	strings.

Patches:
http://sourceware.org/cgi-bin/cvsweb.cgi/src/gdb/ChangeLog.diff?cvsroot=src&r1=1.11587&r2=1.11588
http://sourceware.org/cgi-bin/cvsweb.cgi/src/gdb/python/py-lazy-string.c.diff?cvsroot=src&r1=1.2&r2=1.3
http://sourceware.org/cgi-bin/cvsweb.cgi/src/gdb/testsuite/ChangeLog.diff?cvsroot=src&r1=1.2226&r2=1.2227
http://sourceware.org/cgi-bin/cvsweb.cgi/src/gdb/testsuite/gdb.python/py-value.c.diff?cvsroot=src&r1=1.4&r2=1.5
http://sourceware.org/cgi-bin/cvsweb.cgi/src/gdb/testsuite/gdb.python/py-value.exp.diff?cvsroot=src&r1=1.7&r2=1.8


------- Additional Comments From pmuldoon at redhat dot com  2010-04-08 10:30 -------
Commited fix upstream, see comment #2.

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|                            |FIXED
   Target Milestone|7.1                         |7.2


http://sourceware.org/bugzilla/show_bug.cgi?id=11417

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