[Tcl-bugs] [ tcl-Patches-1259431 ] Check for 0 byte allocation in ckalloc

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Patches item #1259431, was opened at 2005-08-15 02:03
Message generated for change (Comment added) made by dkf
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Category: 40. Memory Allocation
Group: None
Status: Open
Resolution: None
Priority: 2
Submitted By: Mo DeJong (mdejong)
Assigned to: Jeffrey Hobbs (hobbs)
Summary: Check for 0 byte allocation in ckalloc

Initial Comment:
I ran into a little problem where a bug in code to call
ckalloc ended up trying to allocate 0 bytes. That
crashed in the Win32 malloc when compiled with
Mingw. I can't see any reason to allow a zero byte
allocation, and it seems like adding a test like the
following could not hurt. Any objections?

--- generic/tclCkalloc.c        19 Jan 2003 07:21:18
-0000      1.19
+++ generic/tclCkalloc.c        15 Aug 2005 00:59:24 -0000
@@ -373,6 +373,10 @@
     if (validate_memory)
         Tcl_ValidateAllMemory (file, line);

+    if (size == 0) {
+        panic("attempt to ckalloc 0 bytes, %s line
%d", size, file, line);
+    }
+
     result = (struct mem_header *)
TclpAlloc((unsigned)size +
                               sizeof(struct
mem_header) + HIGH_GUARD_SIZE);
     if (result == NULL) {


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>Comment By: Donal K. Fellows (dkf)
Date: 2005-08-15 16:03

Message:
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The core currently checks (in Tcl_Alloc()) to see whether a
NULL low-level alloc result is coming from asking for zero
bytes; if so, it *doesn't* panic. This indicates that
panic-ing on zero-alloc is probably wrong.

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

Comment By: Joe Mistachkin (mistachkin)
Date: 2005-08-15 02:33

Message:
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user_id=113501

I don't think we should take this patch, it breaks
compatibility with malloc(), which is technically allowed to
allocate a "zero byte item" and return it.

The ANSI C standard states that this is "implementation
defined"; however, we should probably just treat it as a one
byte request.


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