Merge pull request #21952 from r30shah/backport21938

(0.53) Disable System.nanoTime acceleration under AOT on Z

Author: pshipton

runtime/compiler/z/codegen/J9CodeGenerator.cpp

@@ -228,8 +228,13 @@ J9::Z::CodeGenerator::initialize()
    // Enable high-resolution timer for System.nanoTime() unless we need to support checkpointing (i.e. snapshot mode), which requires
    // that we adjust nanoTime() after restoring checkpoints. This adjustment is currently not implemented for the high res timer, hence
    // we need to stick to the Java nanoTime() implementation.
-   if (!fej9->isSnapshotModeEnabled())
+   // In case of generating a portable code, even though we would not suffer the same issue of adjustment required, in case such code is
+   // used in application that will be checkpointed, it will suffer the same issue of unsupported nanoTime() adjustment for high res timer.
+   // As currently Snapshot mode is available on Linux on Z only, disabling the acceleration on Linux when we are generating portable code.
+   if (!(fej9->isSnapshotModeEnabled() || (comp->target().isLinux() && comp->compilePortableCode())))
+      {
       cg->setSupportsCurrentTimeMaxPrecision();
+      }
 
    // Support BigDecimal Long Lookaside versioning optimizations.
    if (!comp->getOption(TR_DisableBDLLVersioning))