JDK-8180612 : [ppc] assert failure in cpu/ppc/vm/assembler_ppc.hpp due to immediate value out of range
  • Type: Bug
  • Component: hotspot
  • Sub-Component: compiler
  • Affected Version: 9,10
  • Priority: P3
  • Status: Resolved
  • Resolution: Fixed
  • OS: linux,aix
  • CPU: ppc
  • Submitted: 2017-05-18
  • Updated: 2017-08-25
  • Resolved: 2017-05-25
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JDK 10
10 b21Fixed
Related Reports
Relates :  
JDK-8184800 - Streamline RTM flag validity testing with generic flag testing support
Description
The code emitter for the cmpdi instruction (compare immediate) is called with an out-of-range immediate value. The instruction takes 16bit signed immediates.

The issue is revealed by jtreg test compiler/rtm/locking/TestRTMAbortRatio. It specifies RTM parameters such that the immediate value that goes into the failing instruction exceeds the allowed range. Specifically, the following setting triggers the assert failure:
  -XX:RTMLockingThreshold=<x> -XX:RTMTotalCountIncrRate=<y>
Any combination where <x>/<y> yields a value outside the range [-32768..32767] will fail. The faulty code is in macroAssembler_ppc.cpp (rtm_abort_ratio_calculation).

This issue will surface only on machines with Power8 or newer processors. In addition, the operating system must support RTM (Linux: kernel version > 4.1, AIX: Rel. >= 7.2).

There is a similar issue in x86 code (same function). It's only similar because it will not immediately cause an assert failure or the like. In addition, the above mentioned quotient must exceed +/-2**31. Then, the quotient (calculated as 64bit int) will be truncated to 32bit and that value be used for comparison.