[Python-Dev] Wg: Re: [Python-checkins] cpython (3.4): Issue #23446: Use PyMem_New instead of PyMem_Malloc to avoid possible integer

 == == == == == == Weitergeleitete Nachricht == == == == == == 
Absender : Stefan Krah<ste...@bytereef.org>
Empfänger : "Victor Stinner"<vict...@gmail.com>
Datum : So, 01 Mrz 2015 18:58:43 +0000
Betreff : Re: [Python-Dev] [Python-checkins] cpython (3.4): Issue #23446: Use PyMem_New instead of PyMem_Malloc to avoid possible integer
 == == == == == == Weitergeleitete Nachricht == == == == == == 

On Mon, Feb 16, 2015 at 10:14:59PM +0100, Victor Stinner wrote: 
> 2015-02-16 17:34 GMT+01:00 Stefan Krah <ste...@bytereef.org>: 
> > 
> > On Mon, Feb 16, 2015 at 11:35:52AM +0000, serhiy.storchaka wrote: 
> >> diff --git a/Modules/_testbuffer.c b/Modules/_testbuffer.c 
> >> --- a/Modules/_testbuffer.c 
> >> +++ b/Modules/_testbuffer.c 
> >> @@ -850,7 +850,7 @@ 
> >> Py_ssize_t *dest; 
> >> Py_ssize_t x, i; 
> >> 
> >> - dest = PyMem_Malloc(len * (sizeof *dest)); 
> >> + dest = PyMem_New(Py_ssize_t, len); 
> >> if (dest == NULL) { 
> >> PyErr_NoMemory(); 
> >> return NULL; 
> > 
> > This, too, was already protected by len == ndim <= 64. 
> 
> I don't understand why you don't want to use PyMem_New() even if it 
> cannot overflow. PyMem_New() is more readable no? 
 
It's readable, but I don't see a reason to change code that already has an 
overflow analysis, especially in 3.4. 
 
As I wrote in http://bugs.python.org/issue23446#msg235770 , people need to 
see that one *can* make certain assumptions about PEP-3118 buffers (otherwise 
one would go insane with overflow checks when doing arithmetic on the buffers. 
 
 
So, in a sense, this commit removes information for the reader. I would 
prefer an "assert(len <= 64)" for documentation purposes while keeping the 
multiplication. 
 
 
 
Stefan Krah