kmalloc() with size zero

kmalloc() with size zero

[Stephane Eranian]

Hello,

I ran into an issue with perfmon where I ended up calling
kmalloc() with a size of zero. To my surprise, this did
not return NULL but a valid data address.

I am wondering if this is a property of kmalloc() or simply
a bug. It is the case that the __kmalloc() code does not
check for zero size.

Thanks,

-- 

-Stephane

Re: kmalloc() with size zero

[Jan Engelhardt]

On Mar 22 2007 16:18, Stephane Eranian wrote:
>
>Hello,
>
>I ran into an issue with perfmon where I ended up calling
>kmalloc() with a size of zero. To my surprise, this did
>not return NULL but a valid data address.
>
>I am wondering if this is a property of kmalloc() or simply
>a bug. It is the case that the __kmalloc() code does not
>check for zero size.

I'd say "feature", glibc's malloc also returns an address on malloc(0).


Jan
-- 

Re: kmalloc() with size zero

[Vignesh Babu BM]

On Fri, 2007-03-23 at 07:08 +0530, Jan Engelhardt wrote:
> 
> On Mar 22 2007 16:18, Stephane Eranian wrote:
> >
> I'd say "feature", glibc's malloc also returns an address on
> malloc(0).
> 
This is implementation defined-the standard allows for return of either
null or an address.
> 
> Jan
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Re: kmalloc() with size zero

[Folkert van Heusden]

> > I'd say "feature", glibc's malloc also returns an address on
> > malloc(0).
> > 
> This is implementation defined-the standard allows for return of either
> null or an address.

Entirely for entertainment: AIX (5.3) returns NULL, IRIX returns a valid
address.


Folkert van Heusden

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Re: kmalloc() with size zero

[Stephane Eranian]

Hi,

On Sun, Mar 25, 2007 at 06:30:34PM +0200, Folkert van Heusden wrote:
> > > I'd say "feature", glibc's malloc also returns an address on
> > > malloc(0).
> > > 
> > This is implementation defined-the standard allows for return of either
> > null or an address.
> 
> Entirely for entertainment: AIX (5.3) returns NULL, IRIX returns a valid
> address.
> 
That's interesting, so many different behaviors! Personally, I still prefer
when malloc(0) returns zero because it makes it easier to catch errors.

-- 

-Stephane

Re: kmalloc() with size zero

[Bill Davidsen]

Stephane Eranian wrote:
> Hi,
> 
> On Sun, Mar 25, 2007 at 06:30:34PM +0200, Folkert van Heusden wrote:
>>>> I'd say "feature", glibc's malloc also returns an address on
>>>> malloc(0).
>>>>
>>> This is implementation defined-the standard allows for return of either
>>> null or an address.
>> Entirely for entertainment: AIX (5.3) returns NULL, IRIX returns a valid
>> address.
>>
> That's interesting, so many different behaviors! Personally, I still prefer
> when malloc(0) returns zero because it makes it easier to catch errors.
> 
Exactly, the address returned is not really useful, the improved error 
checking is useful.

-- 
Bill Davidsen <davidsen@tmr.com>
   "We have more to fear from the bungling of the incompetent than from
the machinations of the wicked."  - from Slashdot

Re: kmalloc() with size zero

[Christoph Lameter]

On Thu, 22 Mar 2007, Stephane Eranian wrote:

> I ran into an issue with perfmon where I ended up calling
> kmalloc() with a size of zero. To my surprise, this did
> not return NULL but a valid data address.
> 
> I am wondering if this is a property of kmalloc() or simply
> a bug. It is the case that the __kmalloc() code does not
> check for zero size.

Correct SLAB will give you the smallest possible allocation. I'd say these 
calls should be fixed. SLUB does check for zero and will throw a stack 
dump.