[Bug malloc/14981] New: mtrace realloc

[Bug malloc/14981] New: mtrace realloc

[joost.vandevondele at mat dot ethz.ch]

http://sourceware.org/bugzilla/show_bug.cgi?id=14981

             Bug #: 14981
           Summary: mtrace realloc
           Product: glibc
           Version: unspecified
            Status: NEW
          Severity: normal
          Priority: P2
         Component: malloc
        AssignedTo: unassigned@sourceware.org
        ReportedBy: joost.vandevondele@mat.ethz.ch
    Classification: Unclassified


The following program causes mtrace.pl to report memory leaks.

> cat test.c
void main()
{ 
  int* i;
  mtrace();
  i=malloc(sizeof(int));
  i=realloc(i,0);
  muntrace();
} 

mtrace ./t.dat 

Memory not freed:
-----------------
           Address     Size     Caller
0x0000000000a96460      0x4  at 0x400678

It looks like mtrace.pl is not considering realloc(x,0) equivalent to a free.

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[Bug malloc/14981] mtrace realloc

[joost.vandevondele at mat dot ethz.ch]

http://sourceware.org/bugzilla/show_bug.cgi?id=14981

Joost VandeVondele <joost.vandevondele at mat dot ethz.ch> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |joost.vandevondele at mat
                   |                            |dot ethz.ch

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[Bug malloc/14981] mtrace realloc

[bugdal at aerifal dot cx]

http://sourceware.org/bugzilla/show_bug.cgi?id=14981

Rich Felker <bugdal at aerifal dot cx> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |bugdal at aerifal dot cx

--- Comment #1 from Rich Felker <bugdal at aerifal dot cx> 2012-12-23 02:31:08 UTC ---
This program has a memory leak. On glibc, malloc(0) and realloc(i, 0) both
return a unique pointer that cannot be dereferenced. Failure to free this
pointer is a memory leak.

realloc(i, 0) is only equivalent to free(i) on implementations where malloc(0)
returns 0.

I suspect you're confused by the language in POSIX that says "If size is 0 and
ptr is not a null pointer, the object pointed to is freed." This does not
preclude a memory leak. Note that POSIX later says "If size is 0, either a null
pointer or a unique pointer that can be successfully passed to free() shall be
returned." The confusion stems from the fact that POSIX has misleadingly
reworded the specification of free to refer to "changing the size of an
object", a concept which ISO C intentionally avoids. In the ISO C language, a
successful realloc _always_ frees the original object, and returns a pointer to
a new object with the same contents (up to the minimum of the old and new
size).

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[Bug malloc/14981] mtrace realloc

[schwab@linux-m68k.org]

http://sourceware.org/bugzilla/show_bug.cgi?id=14981

--- Comment #2 from Andreas Schwab <schwab@linux-m68k.org> 2012-12-23 08:36:20 UTC ---
In glibc realloc(0,s) == malloc(s), and realloc(i,0) == (free(i),0) for i != 0.

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[Bug malloc/14981] mtrace realloc

[joseph at codesourcery dot com]

http://sourceware.org/bugzilla/show_bug.cgi?id=14981

--- Comment #3 from joseph at codesourcery dot com <joseph at codesourcery dot com> 2012-12-23 16:31:05 UTC ---
Regarding realloc with size 0, see also 
<http://www.open-std.org/jtc1/sc22/wg14/www/docs/dr_400.htm>.  Some of the 
problems with its semantics arose out of a change in C99 to the wording 
that was used in C90.

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[Bug malloc/14981] mtrace realloc

[schwab@linux-m68k.org]

http://sourceware.org/bugzilla/show_bug.cgi?id=14981

Andreas Schwab <schwab@linux-m68k.org> changed:

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

--- Comment #4 from Andreas Schwab <schwab@linux-m68k.org> 2013-01-03 10:20:41 UTC ---
Fixed in 2.18.

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[Bug malloc/14981] mtrace realloc

[jackie.rosen at hushmail dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=14981

Jackie Rosen <jackie.rosen at hushmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jackie.rosen at hushmail dot com

--- Comment #5 from Jackie Rosen <jackie.rosen at hushmail dot com> ---
*** Bug 260998 has been marked as a duplicate of this bug. ***
Seen from the domain http://volichat.com
Page where seen: http://volichat.com/adult-chat-rooms
Marked for reference. Resolved as fixed @bugzilla.

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[Bug malloc/14981] mtrace realloc

[schwab at sourceware dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=14981

Andreas Schwab <schwab at sourceware dot org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|jackie.rosen at hushmail dot com   |

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[Bug malloc/14981] mtrace realloc

[fweimer at redhat dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=14981

Florian Weimer <fweimer at redhat dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
              Flags|                            |security-

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