8330094: RISC-V: Save and restore FRM in the call stub

Reviewed-by: fyang
Backport-of: b0496096dc8d7dc7acf28aa006141a3ecea446de

src/hotspot/cpu/riscv/frame_riscv.hpp

@@ -133,7 +133,7 @@
     // Entry frames
     // n.b. these values are determined by the layout defined in
     // stubGenerator for the Java call stub
-    entry_frame_after_call_words                     =  34,
+    entry_frame_after_call_words                     =  35,
     entry_frame_call_wrapper_offset                  = -10,
 
     // we don't need a save area

src/hotspot/cpu/riscv/stubGenerator_riscv.cpp

@@ -127,8 +127,9 @@ class StubGenerator: public StubCodeGenerator {
   //     [ return_from_Java     ] <--- sp
   //     [ argument word n      ]
   //      ...
-  // -34 [ argument word 1      ]
-  // -33 [ saved f27            ] <--- sp_after_call
+  // -35 [ argument word 1      ]
+  // -34 [ saved FRM in Floating-point Control and Status Register ] <--- sp_after_call
+  // -33 [ saved f27            ]
   // -32 [ saved f26            ]
   // -31 [ saved f25            ]
   // -30 [ saved f24            ]
@@ -165,8 +166,9 @@ class StubGenerator: public StubCodeGenerator {
 
   // Call stub stack layout word offsets from fp
   enum call_stub_layout {
-    sp_after_call_off  = -33,
+    sp_after_call_off  = -34,
 
+    frm_off            = sp_after_call_off,
     f27_off            = -33,
     f26_off            = -32,
     f25_off            = -31,
@@ -214,6 +216,7 @@ class StubGenerator: public StubCodeGenerator {
 
     const Address sp_after_call (fp, sp_after_call_off  * wordSize);
 
+    const Address frm_save      (fp, frm_off            * wordSize);
     const Address call_wrapper  (fp, call_wrapper_off   * wordSize);
     const Address result        (fp, result_off         * wordSize);
     const Address result_type   (fp, result_type_off    * wordSize);
@@ -296,6 +299,16 @@ class StubGenerator: public StubCodeGenerator {
     __ fsd(f26, f26_save);
     __ fsd(f27, f27_save);
 
+    __ frrm(t0);
+    __ sd(t0, frm_save);
+    // Set frm to the state we need. We do want Round to Nearest. We
+    // don't want non-IEEE rounding modes.
+    Label skip_fsrmi;
+    guarantee(__ RoundingMode::rne == 0, "must be");
+    __ beqz(t0, skip_fsrmi);
+    __ fsrmi(__ RoundingMode::rne);
+    __ bind(skip_fsrmi);
+
     // install Java thread in global register now we have saved
     // whatever value it held
     __ mv(xthread, c_rarg7);
@@ -413,6 +426,14 @@ class StubGenerator: public StubCodeGenerator {
 
     __ ld(x9, x9_save);
 
+    // restore frm
+    Label skip_fsrm;
+    __ ld(t0, frm_save);
+    __ frrm(t1);
+    __ beq(t0, t1, skip_fsrm);
+    __ fsrm(t0);
+    __ bind(skip_fsrm);
+
     __ ld(c_rarg0, call_wrapper);
     __ ld(c_rarg1, result);
     __ ld(c_rarg2, result_type);