Problem of using malloc() without including stdlib.h

Jonathan Lu luchsh at
Fri Feb 3 08:47:22 UTC 2012

Sorry for being absent from this thread so long, I just experienced 
couple of days with very limited Internet access.

Actually the problem was firstly found on AIX platform, on which 
sizeof(malloc(1)) without including <stdlib.h> will always give 4 
instead of 8. The symptom was runtime segment error not compiling time 
warnings, and I suspect there're more failures which were not covered in 
my application.

I've checked the build log of Linux64 platform, as Phil mentioned 
there's also no such warnings except for the hotspot diagnostic ones. 
One reason might be that some code inlcudes "malloc.h" instead of 
<stdlib.h>, there's one 'extern' definition in malloc.h on Linux 64 
platform, but I do not see one on AIX platform. I've also tried to trace 
the indirect reference relation ship for all the .c/.cpp files using 
malloc(), still cannot determine a explicit definition of following 
files. pls fix me if anything wrong, because the list is produced 
manually :(


For a simple HelloWorld.c, if we use malloc() without including 
stdlib.h, it will give warnings like "warning: incompatible implicit 
declaration of built-in function ‘malloc’". No such warning were found 
from the build log for above files, so I guess there must be some 
headers has got indirect including or declaration of malloc.h, but I'm 
worried because I did not see one via manual search. It indeed sounds 
reasonable to me that if no warnings are produced and the compilation 
runs OK, we may just leave the code untouched, but it will improve 
portability if we can explicitly includes standard C library headers in 
the right place (of cause, the 'right' place is also something need to 
be discussed), right?

And for the 3rd party libraries, for those whose code has been shipped 
with OpenJDK source, they seem OK to me since malloc() has either been 
included or redefined. But for some dependency libraries of compilation, 
such as X11 dev, are they also trustworthy?

Best regards!
- Jonathan

On 01/19/2012 02:31 AM, Kelly O'Hair wrote:
> A webrev and a code review from the appropriate teams is indeed needed.
> -kto
> On Jan 18, 2012, at 9:56 AM, Phil Race wrote:
>> Its arguable, whether harmless or not, that each file needs to include it.
>> Its not unreasonable for an area of the code to have a header file such as "awt.h"
>> that is supposed to be the one that's included by the other files in that area of
>> the code, and which takes care of common includes. jni_util.h is not necessarily it.
>> There isn't a need for every file to include that.
>> Also many files are 3rd party libs and I don't like editing those as the changes
>> really belong upstream.
>> So a one size fits all approach might be the answer but I'd want to make sure
>> of that first.
>> So I'd like to see the list of files that generate actual warnings as well as the list
>> of files that reference malloc but don't include stdlib.h.
>> We are well aware that returning int as a default is bad in 64 bit .. I'd expect
>> instant death so I'd like to see those actual warnings rather than just the
>> theoretical ones.
>> My grep of a current JDK 8 build log for 64 bit Linux shows the only malloc warnings
>> are in hotspot management code. So I am waiting for the proof of the real problem
>> And I can speak for 2d, and if there's 2D files touched I would like to see any changes
>> to those files, and the reasoning discussed on 2d-dev ..
>> -phil.
>> On 1/18/2012 8:26 AM, Kelly O'Hair wrote:
>>> On Jan 18, 2012, at 12:19 AM, Jonathan Lu wrote:
>>>> Hi core-libs-dev,
>>>> I found that for some native code of OpenJDK code base, malloc() is used without including header file stdlib.h, such as following files,
>>>> ./src/solaris/native/sun/java2d/opengl/GLXSurfaceData.c
>>>> ./src/solaris/native/sun/java2d/x11/XRBackendNative.c
>>>> ....
>>>> I assume that there's no hacking tricks involved here, right? because this may cause problem for some C compilers, which assumes 'int' as the default return type of a function if it cannot find the function's declaration during compiling. Under such a condition, actual return result of type 'void*' from malloc() will be converted to 'int', which may result in truncated pointers in 64bit platforms. If the application tries to dereference such a broken pointer, error will occur.
>>>> Indeed I found some indirect includes of stdlib.h, but there're still some I do not see a stdlib.h get included from any of  the direct/indirect included headers. I think in order to fix this problem, two approaches may be considered here,
>>>> a) add "#include<stdlib.h>" to every missing .c file.
>>>> b) add "#include<stdlib.h>" to a commonly  referenced header file, such as jni_util.h. but it would not be easy to find such a file for all and creating one is the same as approach a).
>>> I suggest a)  It should be harmless and is the right thing to do.
>>> It's been a while since I studied the C standard, but I vaguely recall that there was another standard C include file
>>> that would cause the malloc() prototype declaration to show up.
>>> Or maybe it wasn't a standard one.  In any case, I think your a) approach is correct and I don't see much a need
>>> for detailed discussions on this, as long as it builds correctly with no warnings on all platforms. It should be fine and correct.
>>> That's my 2 cents.
>>> -kto
>>>> But both methods need to change many files, any other ideas about how to fix it more elegantly?
>>>> Thanks and best regards!
>>>> - Jonathan

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