RFR: 8187578: BitMap::reallocate should check if old_map is NULL

[Erik Österlund]

Looks good.

/Erik

On 2017-09-15 15:04, Erik Helin wrote:
> Hi all,
>
> I'm still trying to compile with gcc 7.1.1 and run into another small 
> issue. BitMap::reallocate calls Copy::disjoint_words and there is a 
> case in Copy::disjoint_words that might result in call to memcpy. The 
> problem is that BitMap::reallocate does not check that the "from" 
> argument to Copy::disjoint_words differs from NULL, and a call to 
> memcpy with a NULL argument is undefined behavior.
>
> Webrev:
> http://cr.openjdk.java.net/~ehelin/8187578/00/
>
> Patch:
> --- old/src/hotspot/share/utilities/bitMap.cpp    2017-09-15 
> 14:47:21.471113699 +0200
> +++ new/src/hotspot/share/utilities/bitMap.cpp    2017-09-15 
> 14:47:21.179112252 +0200
> @@ -81,8 +81,10 @@
>    if (new_size_in_words > 0) {
>      map = allocator.allocate(new_size_in_words);
>
> -    Copy::disjoint_words((HeapWord*)old_map, (HeapWord*) map,
> -                         MIN2(old_size_in_words, new_size_in_words));
> +    if (old_map != NULL) {
> +      Copy::disjoint_words((HeapWord*)old_map, (HeapWord*) map,
> +                           MIN2(old_size_in_words, new_size_in_words));
> +    }
>
>      if (new_size_in_words > old_size_in_words) {
>        clear_range_of_words(map, old_size_in_words, new_size_in_words);
>
> Thanks,
> Erik