I don't recall if we ever promised that this case would work without
aliasing issues. I know that we went out of our way in the copyArea
method to prevent the aliasing issue, doing the blits piecemeal so that
they don't interfere with each other. Further, while it may be easy
enough to just call memmove to have the libraray do this for us in the
IsoBlit case, other cases that don't fall into the IsoBlit macro will
not be similarly protected. In particular, if you specify an alpha
value, you will not get this protection (at least not without a huge
amount of work to overhaul the entire DrawImage pipeline).
I would say that this would be OK if we planned to make this promise
about drawImage across all image formats and composition modes, but that
would be a far more complicated fix. Until then, we should not open
this can of worms by modifying this one specific Blit case...
...jim
On 5/25/2015 5:35 AM, Sergey Bylokhov wrote:
Hello.
Please review the fix forjdk9.
I found this issue during code review of another task, related to
performance.
The sample code below will call the IsomorphicCopy method which call
memcpy on the overlapping memory(this is the simplest example)
BufferedImage img = new BufferedImage(100, 100,
BufferedImage.TYPE_INT_ARGB_PRE);
Graphics2D g = img.createGraphics();
g.setComposite(AlphaComposite.Src);
g.drawImage(img, 0, 0, null);
g.dispose();
http://linux.die.net/man/3/memcpy
"The memcpy() function copies n bytes from memory area src to memory
area dest. The memory areas must not overlap. Use memmove(3) if the
memory areas do overlap"
I can confirm this bug using valgrind and a program above:
command:
valgrind --smc-check=all --tool=memcheck --leak-check=full -v
./9/client/build/linux-x86_64-normal-server-fastdebug/images/jdk/bin/java -Xint
Main
output:
==60975== Source and destination overlap in memcpy(0xe1b8b4d8,
0xe1b8b4d8, 400)
==60975== at 0x4C2F71C: memcpy@@GLIBC_2.14 (in
/usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==60975== by 0x1E0F504D: AnyIntIsomorphicCopy (in
/moe/workspaces/jdk/9/client-work/build/linux-x86_64-normal-server-fastdebug/images/jdk/lib/amd64/libawt.so)
==60975== by 0x1E0F5DE8: Java_sun_java2d_loops_Blit_Blit (in
/moe/workspaces/jdk/9/client-work/build/linux-x86_64-normal-server-fastdebug/images/jdk/lib/amd64/libawt.so)
Bug: https://bugs.openjdk.java.net/browse/JDK-8080847
Webrev can be found at: http://cr.openjdk.java.net/~serb/8080847/webrev.00
