Hi, Jim.
Actually there is a difference in support: it works but result is a
little bit wrong, and it does not work and crashes. This fix is not a
general solution for the incorrect result of the blit+aliasing, but for
the possible crash of memcpy especially after some improvements like in
glibc. I think this still an issue.
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
--
Best regards, Sergey.
