find command with gdb v7.0

find command with gdb v7.0

[James Pandavan]

Hi,

I wanted to try out the new find command wivh gdb v7.0. I used the 
example given in this page 
(http://sourceware.org/gdb/current/onlinedocs/gdb_11.html#SEC91). I just 
added one line (line no 5) to the example given. It looks like the 
search doesn't start at given location.

In the attached output, you can see that the find command says it 
couldn't find the first word or part of it, but is able to find the 
second word. Is it a bug, or am I doing something wrong?

(gdb) find greet,+100,"greetings"
Pattern not found.
(gdb) find greet,+100,"ings"
Pattern not found.

Thanks,
James Pandavan

---------------------------------------------------------------------------------------------------------- 


GNU gdb (GDB) 7.0-ubuntu
Copyright (C) 2009 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-linux-gnu".
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>...
Reading symbols from 
/tmp/gdb/gdb_7.0-0ubuntu1_amd64/data/usr/bin/a.out...done.
(gdb) break main
Breakpoint 1 at 0x4005f4: file test.cpp, line 5.
(gdb) list 3,12
3 int main()
4 {
5 char * greet="greetings gentleman";
6 static char hello[] = "hello-hello";
7 static struct { char c; short s; int i; }
8 __attribute__ ((packed)) mixed
9 = { 'c', 0x1234, 0x87654321 };
10 printf ("%s\n", hello);
11 return(0);
12 }
(gdb) run

Breakpoint 1, main () at test.cpp:5
5 char * greet="greetings gentleman";
(gdb) n
10 printf ("%s\n", hello);
(gdb) p greet
$1 = 0x4006fc "greetings gentleman"
(gdb) find greet,+100,"greetings"
Pattern not found.
(gdb) find greet,+100,"ings"
Pattern not found.
(gdb) find greet,+100,"gentleman"
0x400706
1 pattern found.
(gdb)

Re: find command with gdb v7.0

[Paul Pluzhnikov]

On Tue, Oct 27, 2009 at 3:07 AM, James Pandavan
<james.pandavan@googlemail.com> wrote:

> I wanted to try out the new find command wivh gdb v7.0. I used the example
> given in this page
> (http://sourceware.org/gdb/current/onlinedocs/gdb_11.html#SEC91). I just
> added one line (line no 5) to the example given. It looks like the search
> doesn't start at given location.
>
> In the attached output, you can see that the find command says it couldn't
> find the first word or part of it, but is able to find the second word. Is
> it a bug, or am I doing something wrong?
>
> (gdb) find greet,+100,"greetings"
> Pattern not found.
> (gdb) find greet,+100,"ings"
> Pattern not found.

This currently searches for a sequence of bytes 'i', 'n', 'g', 's', '\0'.

There is in fact no such sequence of bytes in your program, which is why
you get "not found" answer. I'll grant you that it is not what one might
reasonably expect, and the manual doesn't explicitly say the terminating
NUL is included in the search pattern.

I think removing the trailing NUL is a better fix; one could always put
it back with

  find greet,+100,"gentleman",'\0'

if one is really interested in the string with terminating NUL, whereas
currently you'd have to spell each byte separately, which is rather
inconvenient:

  (gdb) p greet
  $1 = 0x4005a8 "greetings gentleman"

  (gdb) find greet,+100,'g','r','e','e','t','i','n','g','s'
  0x4005a8
  1 pattern found.

Feel free to open a GDB enhancement request for this.

>
> Thanks,
> James Pandavan
>
> ----------------------------------------------------------------------------------------------------------
>
> GNU gdb (GDB) 7.0-ubuntu
> Copyright (C) 2009 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-linux-gnu".
> For bug reporting instructions, please see:
> <http://www.gnu.org/software/gdb/bugs/>...
> Reading symbols from
> /tmp/gdb/gdb_7.0-0ubuntu1_amd64/data/usr/bin/a.out...done.
> (gdb) break main
> Breakpoint 1 at 0x4005f4: file test.cpp, line 5.
> (gdb) list 3,12
> 3 int main()
> 4 {
> 5 char * greet="greetings gentleman";
> 6 static char hello[] = "hello-hello";
> 7 static struct { char c; short s; int i; }
> 8 __attribute__ ((packed)) mixed
> 9 = { 'c', 0x1234, 0x87654321 };
> 10 printf ("%s\n", hello);
> 11 return(0);
> 12 }
> (gdb) run
>
> Breakpoint 1, main () at test.cpp:5
> 5 char * greet="greetings gentleman";
> (gdb) n
> 10 printf ("%s\n", hello);
> (gdb) p greet
> $1 = 0x4006fc "greetings gentleman"
> (gdb) find greet,+100,"greetings"
> Pattern not found.
> (gdb) find greet,+100,"ings"
> Pattern not found.
> (gdb) find greet,+100,"gentleman"
> 0x400706
> 1 pattern found.
> (gdb)
>
>
>
>
>



-- 
Paul Pluzhnikov

Re: find command with gdb v7.0

[Doug Evans]

On Tue, Oct 27, 2009 at 11:36 AM, Paul Pluzhnikov
<ppluzhnikov@google.com> wrote:
< [...] the manual doesn't explicitly say the terminating
> NUL is included in the search pattern.

Well, it does, but perhaps it's in a place that's easily missed.

> I think removing the trailing NUL is a better fix; one could always put
> it back with
>
>  find greet,+100,"gentleman",'\0'

Or "gentleman\0".

Re: find command with gdb v7.0

[James Pandavan]

Doug Evans wrote:
> On Tue, Oct 27, 2009 at 11:36 AM, Paul Pluzhnikov
> <ppluzhnikov@google.com> wrote:
> < [...] the manual doesn't explicitly say the terminating
>   
>> NUL is included in the search pattern.
>>     
>
> Well, it does, but perhaps it's in a place that's easily missed.
>
>   
I could see the '\0' termination assumption for c/c++ mentioned in the 
doc now. Don't know how I missed it before. Thanks.