8294087: RISC-V: RVC: Fix a potential alignment issue and add more alignment assertions for the patchable calls/nops

Reviewed-by: shade, fjiang, fyang

src/hotspot/cpu/riscv/c1_LIRAssembler_riscv.cpp

@@ -1349,7 +1349,7 @@ void LIR_Assembler::align_call(LIR_Code code) {
   // With RVC a call instruction may get 2-byte aligned.
   // The address of the call instruction needs to be 4-byte aligned to
   // ensure that it does not span a cache line so that it can be patched.
-  __ align(4);
+  __ align(NativeInstruction::instruction_size);
 }
 
 void LIR_Assembler::call(LIR_OpJavaCall* op, relocInfo::relocType rtype) {
@@ -1372,7 +1372,7 @@ void LIR_Assembler::ic_call(LIR_OpJavaCall* op) {
 
 void LIR_Assembler::emit_static_call_stub() {
   address call_pc = __ pc();
-  assert((__ offset() % 4) == 0, "bad alignment");
+  MacroAssembler::assert_alignment(call_pc);
   address stub = __ start_a_stub(call_stub_size());
   if (stub == NULL) {
     bailout("static call stub overflow");

src/hotspot/cpu/riscv/c1_MacroAssembler_riscv.cpp

@@ -323,7 +323,7 @@ void C1_MacroAssembler::verified_entry(bool breakAtEntry) {
   // first instruction with a jump. For this action to be legal we
   // must ensure that this first instruction is a J, JAL or NOP.
   // Make it a NOP.
-
+  assert_alignment(pc());
   nop();
 }
 

src/hotspot/cpu/riscv/c2_MacroAssembler_riscv.cpp

@@ -255,7 +255,7 @@ void C2_MacroAssembler::emit_entry_barrier_stub(C2EntryBarrierStub* stub) {
 
   bind(stub->guard());
   relocate(entry_guard_Relocation::spec());
-  assert(offset() % 4 == 0, "bad alignment");
+  assert_alignment(pc());
   emit_int32(0);  // nmethod guard value
   // make sure the stub with a fixed code size
   if (alignment_bytes == 2) {

src/hotspot/cpu/riscv/gc/shared/barrierSetAssembler_riscv.cpp

@@ -262,7 +262,7 @@ void BarrierSetAssembler::nmethod_entry_barrier(MacroAssembler* masm, Label* slo
 
     __ bind(local_guard);
 
-    assert(__ offset() % 4 == 0, "bad alignment");
+    MacroAssembler::assert_alignment(__ pc());
     __ emit_int32(0); // nmethod guard value. Skipped over in common case.
     __ bind(skip_barrier);
   } else {

src/hotspot/cpu/riscv/macroAssembler_riscv.cpp

@@ -2828,6 +2828,11 @@ address MacroAssembler::trampoline_call(Address entry) {
   }
 
   address call_pc = pc();
+#ifdef ASSERT
+  if (entry.rspec().type() != relocInfo::runtime_call_type) {
+    assert_alignment(call_pc);
+  }
+#endif
   relocate(entry.rspec());
   if (!far_branches()) {
     jal(entry.target());

src/hotspot/cpu/riscv/macroAssembler_riscv.hpp

@@ -30,6 +30,7 @@
 #include "asm/assembler.hpp"
 #include "code/vmreg.hpp"
 #include "metaprogramming/enableIf.hpp"
+#include "nativeInst_riscv.hpp"
 #include "oops/compressedOops.hpp"
 #include "utilities/powerOfTwo.hpp"
 
@@ -49,6 +50,9 @@ class MacroAssembler: public Assembler {
 
   // Alignment
   int align(int modulus, int extra_offset = 0);
+  static inline void assert_alignment(address pc, int alignment = NativeInstruction::instruction_size) {
+    assert(is_aligned(pc, alignment), "bad alignment");
+  }
 
   // Stack frame creation/removal
   // Note that SP must be updated to the right place before saving/restoring RA and FP

src/hotspot/cpu/riscv/nativeInst_riscv.cpp

@@ -265,6 +265,13 @@ void NativeJump::verify() { }
 
 
 void NativeJump::check_verified_entry_alignment(address entry, address verified_entry) {
+  // Patching to not_entrant can happen while activations of the method are
+  // in use. The patching in that instance must happen only when certain
+  // alignment restrictions are true. These guarantees check those
+  // conditions.
+
+  // Must be 4 bytes aligned
+  MacroAssembler::assert_alignment(verified_entry);
 }
 
 
@@ -355,6 +362,8 @@ void NativeJump::patch_verified_entry(address entry, address verified_entry, add
          nativeInstruction_at(verified_entry)->is_sigill_not_entrant(),
          "riscv cannot replace non-jump with jump");
 
+  check_verified_entry_alignment(entry, verified_entry);
+
   // Patch this nmethod atomically.
   if (Assembler::reachable_from_branch_at(verified_entry, dest)) {
     ptrdiff_t offset = dest - verified_entry;

src/hotspot/cpu/riscv/riscv.ad

@@ -1318,6 +1318,7 @@ void MachPrologNode::emit(CodeBuffer &cbuf, PhaseRegAlloc *ra_) const {
 
   // insert a nop at the start of the prolog so we can patch in a
   // branch if we need to invalidate the method later
+  MacroAssembler::assert_alignment(__ pc());
   __ nop();
 
   assert_cond(C != NULL);
@@ -1735,6 +1736,10 @@ void MachUEPNode::emit(CodeBuffer& cbuf, PhaseRegAlloc* ra_) const
   __ cmp_klass(j_rarg0, t1, t0, skip);
   __ far_jump(RuntimeAddress(SharedRuntime::get_ic_miss_stub()));
   __ bind(skip);
+
+  // These NOPs are critical so that verified entry point is properly
+  // 4 bytes aligned for patching by NativeJump::patch_verified_entry()
+  __ align(NativeInstruction::instruction_size);
 }
 
 uint MachUEPNode::size(PhaseRegAlloc* ra_) const

src/hotspot/cpu/riscv/sharedRuntime_riscv.cpp

@@ -938,6 +938,7 @@ nmethod* SharedRuntime::generate_native_wrapper(MacroAssembler* masm,
     int vep_offset = ((intptr_t)__ pc()) - start;
 
     // First instruction must be a nop as it may need to be patched on deoptimisation
+    MacroAssembler::assert_alignment(__ pc());
     __ nop();
     gen_special_dispatch(masm,
                          method,
@@ -1089,6 +1090,7 @@ nmethod* SharedRuntime::generate_native_wrapper(MacroAssembler* masm,
 
   // If we have to make this method not-entrant we'll overwrite its
   // first instruction with a jump.
+  MacroAssembler::assert_alignment(__ pc());
   __ nop();
 
   if (VM_Version::supports_fast_class_init_checks() && method->needs_clinit_barrier()) {