[Bug c/36970] New: GCC should display a warning when trying to free a static array

[Bug c/36970] New: GCC should display a warning when trying to free a static array

[nair dot sajish at gmail dot com]

On Tue, Jul 01, 2008 at 11:37:05AM +0000, Joseph S. Myers wrote:
> On Tue, 1 Jul 2008, Michael Meissner wrote:
> 
> > On Tue, Jul 01, 2008 at 11:50:58AM +0200, Denys Vlasenko wrote:
> > > On Tuesday 01 July 2008 09:24, Sajish V wrote:
> > > > Thanks for the reply, Denys.
> > > > My question was, why doesn't gcc catch it during compilation? It is clear
> > > > that we are trying to free a variable from stack. Shouldn't gcc flag an
> > > > error for this during compilation?
> > 
> > It could.  Nobody has written the code to do so, and as they say patches are
> > welcome (assuming you have done the paperwork to legally contribute to GCC).
> > Have you filed a feature request via bugzilla so that it can be tracked?
> 
> An error is inappropriate; undefined behavior only occurs on execution of 
> the call to free, not on compilation of the program.  A warning would be 
> fine (as would converting the call to free into an abort).

True enough from a standards point of view.  Obviously having a warning would
allow some invalid code to be detected at compilation time.

-- 
Michael Meissner
email: gnu@the-meissners.org
http://www.the-meissners.org

><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><

Thanks for the reply, Denys.
My question was, why doesn't gcc catch it during compilation? It is clear that
we are trying to free a variable from stack. Shouldn't gcc flag an error for
this during compilation?
Regards,
Sajish.



----- Original Message ----
From: Denys Vlasenko <vda.linux@googlemail.com>
To: gcc@gcc.gnu.org
Cc: Sajish V <emailsaju@yahoo.com>
Sent: Tuesday, July 1, 2008 2:44:06 PM
Subject: Re: free (static_array)

On Tuesday 01 July 2008 08:38, Sajish V wrote:
> Hi All, 
> Can you please let me know why GCC does not crib when we try to free a static array?
> main ()
> { 
>      char array[100];
>      free (array);
> }
> The above code compiles without any hitch. 
> Thanks,
> Sajish.

# ./a.out
*** glibc detected *** ./a.out: free(): invalid pointer: 0xffa8b530 ***
======= Backtrace: =========
/lib/libc.so.6[0xf7ecb7a7]
/lib/libc.so.6(__libc_free+0x79)[0xf7ecc0ad]
./a.out[0x804834e]
/lib/libc.so.6(__libc_start_main+0x138)[0xf7e8da74]
./a.out[0x80482b5]
======= Memory map: ========
08048000-08049000 r-xp 00000000 08:06 1315925                           
/.local/tmp/a.out
08049000-0804a000 rwxp 00000000 08:06 1315925                           
/.local/tmp/a.out
0804a000-0806b000 rwxp 0804a000 00:00 0                                  [heap]
f7e6f000-f7e76000 r-xp 00000000 08:05 46193                             
/app/gcc-3.3.3/lib/libgcc_s.so.1
f7e76000-f7e77000 rwxp 00006000 08:05 46193                             
/app/gcc-3.3.3/lib/libgcc_s.so.1
f7e77000-f7e78000 rwxp f7e77000 00:00 0
f7e78000-f7f60000 r-xp 00000000 08:0

--
vda

><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><

Hi All, 
Can you please let me know why GCC does not crib when we try to free a static
array?
main ()
{ 
     char array[100];
     free (array);
}
The above code compiles without any hitch. 
Thanks,
Sajish.


-- 
           Summary: GCC should display a warning when trying to free a
                    static array
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: enhancement
          Priority: P3
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: nair dot sajish at gmail dot com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36970

[Bug c/36970] GCC should display a warning when trying to free a static array

[rguenth at gcc dot gnu dot org]

-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|0                           |1
           Keywords|                            |diagnostic
   Last reconfirmed|0000-00-00 00:00:00         |2008-07-30 08:43:26
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36970

[Bug c/36970] GCC should display a warning when trying to free a static array

[jakub at gcc dot gnu dot org]

-- 

jakub at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         AssignedTo|unassigned at gcc dot gnu   |jakub at gcc dot gnu dot org
                   |dot org                     |
             Status|NEW                         |ASSIGNED
   Last reconfirmed|2008-07-30 08:43:26         |2008-07-30 13:27:50
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36970

[Bug c/36970] GCC should display a warning when trying to free a static array

[jakub at gcc dot gnu dot org]

------- Comment #1 from jakub at gcc dot gnu dot org  2008-07-31 08:04 -------
Subject: Bug 36970

Author: jakub
Date: Thu Jul 31 08:02:49 2008
New Revision: 138362

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=138362
Log:
        PR c/36970
        * builtins.c (maybe_emit_free_warning): New function.
        (expand_builtin): Process BUILT_IN_FREE even at -O0.  Call
        maybe_emit_free_warning for BUILT_IN_FREE.

        * gcc.dg/free-1.c: New test.
        * gcc.dg/free-2.c: New test.

Added:
    trunk/gcc/testsuite/gcc.dg/free-1.c
    trunk/gcc/testsuite/gcc.dg/free-2.c
Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/builtins.c
    trunk/gcc/testsuite/ChangeLog


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36970

[Bug c/36970] GCC should display a warning when trying to free a static array

[jakub at gcc dot gnu dot org]

------- Comment #2 from jakub at gcc dot gnu dot org  2008-07-31 08:52 -------
Implemented on the trunk.


-- 

jakub at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|                            |FIXED


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36970