8330266: RISC-V: Restore frm to RoundingMode::rne after JNI

Reviewed-by: fyang, rehn

src/hotspot/cpu/riscv/downcallLinker_riscv.cpp

@@ -278,6 +278,9 @@ void DowncallLinker::StubGenerator::generate() {
   Label L_reguard;
   Label L_after_reguard;
   if (_needs_transition) {
+    // Restore cpu control state after JNI call
+    __ restore_cpu_control_state_after_jni(t0);
+
     __ block_comment("{ thread native2java");
     __ mv(t0, _thread_in_native_trans);
     __ sw(t0, Address(xthread, JavaThread::thread_state_offset()));

src/hotspot/cpu/riscv/macroAssembler_riscv.cpp

@@ -1167,6 +1167,19 @@ void MacroAssembler::fsflagsi(Register Rd, unsigned imm) {
 
 #undef INSN
 
+void MacroAssembler::restore_cpu_control_state_after_jni(Register tmp) {
+  if (RestoreMXCSROnJNICalls) {
+    Label skip_fsrmi;
+    frrm(tmp);
+    // Set FRM to the state we need. We do want Round to Nearest.
+    // We don't want non-IEEE rounding modes.
+    guarantee(RoundingMode::rne == 0, "must be");
+    beqz(tmp, skip_fsrmi);        // Only reset FRM if it's wrong
+    fsrmi(RoundingMode::rne);
+    bind(skip_fsrmi);
+  }
+}
+
 void MacroAssembler::push_reg(Register Rs)
 {
   addi(esp, esp, 0 - wordSize);

src/hotspot/cpu/riscv/macroAssembler_riscv.hpp

@@ -581,6 +581,9 @@ class MacroAssembler: public Assembler {
   void fsflagsi(Register Rd, unsigned imm);
   void fsflagsi(unsigned imm);
 
+  // Restore cpu control state after JNI call
+  void restore_cpu_control_state_after_jni(Register tmp);
+
   // Control transfer pseudo instructions
   void beqz(Register Rs, const address dest);
   void bnez(Register Rs, const address dest);

src/hotspot/cpu/riscv/sharedRuntime_riscv.cpp

@@ -1748,6 +1748,9 @@ nmethod* SharedRuntime::generate_native_wrapper(MacroAssembler* masm,
   intptr_t return_pc = (intptr_t) __ pc();
   oop_maps->add_gc_map(return_pc - start, map);
 
+  // Verify or restore cpu control state after JNI call
+  __ restore_cpu_control_state_after_jni(t0);
+
   // Unpack native results.
   if (ret_type != T_OBJECT && ret_type != T_ARRAY) {
     __ cast_primitive_type(ret_type, x10);

src/hotspot/cpu/riscv/templateInterpreterGenerator_riscv.cpp

@@ -1157,6 +1157,9 @@ address TemplateInterpreterGenerator::generate_native_entry(bool synchronized) {
   __ get_method(xmethod);
   // result potentially in x10 or f10
 
+  // Restore cpu control state after JNI call
+  __ restore_cpu_control_state_after_jni(t0);
+
   // make room for the pushes we're about to do
   __ sub(t0, esp, 4 * wordSize);
   __ andi(sp, t0, -16);