RFR: 8203223: Signed integer overflow in ImageStrings::hash_code (libjimage.so)

[Severin Gehwolf]

Hi,

Could somebody please review this patch for libjimage.so. It fixes one
instance of undefined behavour (signed integer overflow), which
prevents JDK 11 to build on Fedora 28 (GCC 8) with a rather strange
error:

./build/linux-x86_64-normal-server-fastdebug/support/interim-image/bin/java -version
Error occurred during initialization of VM
java/lang/NoClassDefFoundError: java/lang/Object

The proposed fix is to perform the calculations on a local variable of
unsigned type where overflow is well defined.

Bug: https://bugs.openjdk.java.net/browse/JDK-8203223
webrev: http://cr.openjdk.java.net/~sgehwolf/webrevs/JDK-8203223/webrev.01/

Testing: tools/jlink tests (no new failures), currently running through
jdk-submit.

Thanks,
Severin