Package: gdb
Version: 6.8-3
Severity: important
gdb incorrectly prints some objects passed to functions as value.
i.e. for a c-string holder, data pointer is displayed as pointing on itself (or
this), although it points to a valid allocated mem zone.
I put a demonstrating program below :
bdu...@linux1:/tmp$ cat test.cpp
#include <iostream>
#include <cstring>
using namespace std;
class PTString
{
char * data;
public:
PTString(const char * s) {
data = strdup(s);
}
PTString(const PTString& p) {
data = strdup(p.data);
}
operator const char * () const { return data; }
};
void Do(PTString aStr)
{
PTString lStr = aStr;
int a = 1;
++a;
}
int main()
{
PTString test = "foo";
Do(test);
cout << test << endl;
return 0;
}
when I run gdb on it, aStr displays incorrectly (I had to cut garbage to write
in console-based editor)
but if I cast aStr.data to a char**, it works around the problem, as gdb thinks
data is pointing on itself, it dereferences it to real memory zone. See below.
bdu...@linux1:/tmp$ g++ -g2 test.cpp
bdu...@linux1:/tmp$ gdb a.out
GNU gdb 6.8-debian
Copyright (C) 2008 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 "i486-linux-gnu"...
(gdb) b Do
Breakpoint 1 at 0x8048726: file test.cpp, line 24.
(gdb) r
Starting program: /tmp/a.out
Breakpoint 1, Do (aStr={data = 0xbf8af8a0 "\030\020[...garbage cut...]\001"})
at test.cpp:24
24 PTString lStr = aStr;
(gdb) n
26 int a = 1;
(gdb) p lStr
$1 = {data = 0x9d81028 "foo"}
(gdb) p *(char **)(aStr.data)
$2 = 0x9d81018 "foo"
(gdb) p aStr.data
$3 = 0xbf8af8a0 "\030\020[...garbage cut...]\001"
(gdb) c
Continuing.
foo
Program exited normally.
-- System Information:
Debian Release: 5.0.2
APT prefers stable
APT policy: (500, 'stable')
Architecture: i386 (i686)
Kernel: Linux 2.6.26-2-686 (SMP w/1 CPU core)
Locale: LANG=en_US, LC_CTYPE=en_US (charmap=ISO-8859-1)
Shell: /bin/sh linked to /bin/bash
Versions of packages gdb depends on:
ii libc6 2.7-18 GNU C Library: Shared libraries
ii libexpat1 2.0.1-4 XML parsing C library - runtime li
ii libncurses5 5.7+20081213-1 shared libraries for terminal hand
ii libreadline5 5.2-3.1 GNU readline and history libraries
gdb recommends no packages.
Versions of packages gdb suggests:
pn gdb-doc <none> (no description available)
-- no debconf information
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