[vm, compiler] Update the RISC-V shadow call stack pointer from S2 to GP.

Cf. https://reviews.llvm.org/D146463

TEST=ci (Linux), inspect disassembly (Fuchsia/Android)
Change-Id: I3ef4bc4c3212e80221ec7edaebfa33e9eb1db03d
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/291660
Commit-Queue: Ryan Macnak <rmacnak@google.com>
Reviewed-by: Daco Harkes <dacoharkes@google.com>

runtime/vm/compiler/stub_code_compiler_arm64.cc

@@ -3228,6 +3228,10 @@ void StubCodeCompiler::GenerateJumpToFrameStub() {
   __ mov(THR, R3);
   __ SetupCSPFromThread(THR);
 #if defined(DART_TARGET_OS_FUCHSIA)
+  // We need to restore the shadow call stack pointer like longjmp would,
+  // effectively popping all the return addresses between the Dart exit frame
+  // and Exceptions::JumpToFrame, otherwise the shadow call stack might
+  // eventually overflow.
   __ ldr(R18, Address(THR, target::Thread::saved_shadow_call_stack_offset()));
 #elif defined(USING_SHADOW_CALL_STACK)
 #error Unimplemented

runtime/vm/compiler/stub_code_compiler_riscv.cc

@@ -1317,8 +1317,8 @@ void StubCodeCompiler::GenerateInvokeDartCodeStub() {
   __ lx(TMP2, Address(A3, target::Thread::invoke_dart_code_stub_offset()));
   __ sx(TMP2, Address(SP, 0 * target::kWordSize));
 
-#if defined(DART_TARGET_OS_FUCHSIA)
-  __ sx(S2, Address(A3, target::Thread::saved_shadow_call_stack_offset()));
+#if defined(DART_TARGET_OS_FUCHSIA) || defined(DART_TARGET_OS_ANDROID)
+  __ sx(GP, Address(A3, target::Thread::saved_shadow_call_stack_offset()));
 #elif defined(USING_SHADOW_CALL_STACK)
 #error Unimplemented
 #endif
@@ -3002,8 +3002,12 @@ void StubCodeCompiler::GenerateJumpToFrameStub() {
   __ mv(SP, A1);                 // Stack pointer.
   __ mv(FP, A2);                 // Frame_pointer.
   __ mv(THR, A3);
-#if defined(DART_TARGET_OS_FUCHSIA)
-  __ lx(S2, Address(THR, target::Thread::saved_shadow_call_stack_offset()));
+#if defined(DART_TARGET_OS_FUCHSIA) || defined(DART_TARGET_OS_ANDROID)
+  // We need to restore the shadow call stack pointer like longjmp would,
+  // effectively popping all the return addresses between the Dart exit frame
+  // and Exceptions::JumpToFrame, otherwise the shadow call stack might
+  // eventually overflow.
+  __ lx(GP, Address(THR, target::Thread::saved_shadow_call_stack_offset()));
 #elif defined(USING_SHADOW_CALL_STACK)
 #error Unimplemented
 #endif

runtime/vm/constants_riscv.h

@@ -46,7 +46,7 @@ enum Register {
   ZR = 0,
   RA = 1,
   SP = 2,
-  GP = 3,
+  GP = 3,  // Shadow call stack on Fuchsia and Android
   TP = 4,
   T0 = 5,
   T1 = 6,
@@ -61,7 +61,7 @@ enum Register {
   A5 = 15,  // PP, untagged
   A6 = 16,
   A7 = 17,
-  S2 = 18,  // ShadowCallStack
+  S2 = 18,
   S3 = 19,
   S4 = 20,  // ARGS_DESC_REG
   S5 = 21,  // IC_DATA_REG
@@ -198,19 +198,19 @@ struct InstantiateTAVInternalRegs {
   static constexpr intptr_t kSavedRegisters = 0;
 
   // Additional registers used to probe hash-based caches.
-  static constexpr Register kEntryStartReg = S3;
-  static constexpr Register kProbeMaskReg = S4;
-  static constexpr Register kProbeDistanceReg = S5;
-  static constexpr Register kCurrentEntryIndexReg = S6;
+  static constexpr Register kEntryStartReg = S2;
+  static constexpr Register kProbeMaskReg = S3;
+  static constexpr Register kProbeDistanceReg = S4;
+  static constexpr Register kCurrentEntryIndexReg = S5;
 };
 
 // Registers in addition to those listed in TypeTestABI used inside the
 // implementation of type testing stubs that are _not_ preserved.
 struct TTSInternalRegs {
-  static constexpr Register kInstanceTypeArgumentsReg = S3;
-  static constexpr Register kScratchReg = S4;
-  static constexpr Register kSubTypeArgumentReg = S5;
-  static constexpr Register kSuperTypeArgumentReg = S6;
+  static constexpr Register kInstanceTypeArgumentsReg = S2;
+  static constexpr Register kScratchReg = S3;
+  static constexpr Register kSubTypeArgumentReg = S4;
+  static constexpr Register kSuperTypeArgumentReg = S5;
 
   // Must be pushed/popped whenever generic type arguments are being checked as
   // they overlap with registers in TypeTestABI.
@@ -225,10 +225,10 @@ struct TTSInternalRegs {
 // Registers in addition to those listed in TypeTestABI used inside the
 // implementation of subtype test cache stubs that are _not_ preserved.
 struct STCInternalRegs {
-  static constexpr Register kInstanceCidOrSignatureReg = S3;
-  static constexpr Register kInstanceInstantiatorTypeArgumentsReg = S4;
-  static constexpr Register kInstanceParentFunctionTypeArgumentsReg = S5;
-  static constexpr Register kInstanceDelayedFunctionTypeArgumentsReg = S6;
+  static constexpr Register kInstanceCidOrSignatureReg = S2;
+  static constexpr Register kInstanceInstantiatorTypeArgumentsReg = S3;
+  static constexpr Register kInstanceParentFunctionTypeArgumentsReg = S4;
+  static constexpr Register kInstanceDelayedFunctionTypeArgumentsReg = S5;
 
   static constexpr intptr_t kInternalRegisters =
       (1 << kInstanceCidOrSignatureReg) |
@@ -493,13 +493,10 @@ constexpr RegList kAbiPreservedCpuRegs = R(S1) | R(S2) | R(S3) | R(S4) | R(S5) |
                                          R(S10) | R(S11);
 constexpr int kAbiPreservedCpuRegCount = 11;
 
-// S2 is reserved as the shadow call stack pointer on Fuchsia and Android.
-// Although it is available on Linux, we mark it as reserved unconditionally to
-// avoid adding another dimenision for OS into the extracted runtime offsets.
 constexpr RegList kReservedCpuRegisters =
     R(ZR) | R(TP) | R(GP) | R(SP) | R(FP) | R(TMP) | R(TMP2) | R(PP) | R(THR) |
     R(RA) | R(WRITE_BARRIER_STATE) | R(NULL_REG) | R(DISPATCH_TABLE_REG) |
-    R(FAR_TMP) | R(S2);
+    R(FAR_TMP);
 constexpr intptr_t kNumberOfReservedCpuRegisters =
     Utils::CountOneBits32(kReservedCpuRegisters);
 // CPU registers available to Dart allocator.
@@ -568,8 +565,8 @@ class CallingConventions {
   static constexpr Register kSecondReturnReg = A1;
   static constexpr FpuRegister kReturnFpuReg = FA0;
 
-  // S0=FP, S1=THR, S2=ShadowCallStack
-  static constexpr Register kFfiAnyNonAbiRegister = S3;
+  // S0=FP, S1=THR
+  static constexpr Register kFfiAnyNonAbiRegister = S2;
   static constexpr Register kFirstNonArgumentRegister = T0;
   static constexpr Register kSecondNonArgumentRegister = T1;
   static constexpr Register kStackPointerRegister = SPREG;

runtime/vm/instructions_riscv.cc

@@ -414,10 +414,10 @@ intptr_t TypeTestingStubCallPattern::GetSubtypeTestCachePoolIndex() {
   // where Rn = TypeTestABI::kSubtypeTestCacheReg.
 
   // Ensure the caller of the type testing stub (whose return address is [pc_])
-  // branched via `blr R9` or a pc-relative call.
-  if (*reinterpret_cast<uint16_t*>(pc_ - 2) == 0x9a02) {  // jalr s4
+  // branched via `jalr s3` or a pc-relative call.
+  if (*reinterpret_cast<uint16_t*>(pc_ - 2) == 0x9982) {  // jalr s3
     // indirect call
-    //     xxxx c.jalr s4
+    //     xxxx c.jalr s3
     Register reg;
     intptr_t pool_index = -1;
     InstructionPattern::DecodeLoadWordFromPool(pc_ - 2, &reg, &pool_index);

runtime/vm/simulator_arm64.cc

@@ -3890,6 +3890,9 @@ void Simulator::JumpToFrame(uword pc, uword sp, uword fp, Thread* thread) {
   set_register(nullptr, FP, static_cast<int64_t>(fp));
   set_register(nullptr, THR, reinterpret_cast<int64_t>(thread));
   set_register(nullptr, R31, thread->saved_stack_limit() - 4096);
+#if defined(DART_TARGET_OS_FUCHSIA)
+  set_register(nullptr, R18, thread->saved_shadow_call_stack());
+#endif
   // Set the tag.
   thread->set_vm_tag(VMTag::kDartTagId);
   // Clear top exit frame.

runtime/vm/simulator_riscv.cc

@@ -449,6 +449,9 @@ void Simulator::JumpToFrame(uword pc, uword sp, uword fp, Thread* thread) {
   set_xreg(SP, static_cast<uintx_t>(sp));
   set_xreg(FP, static_cast<uintx_t>(fp));
   set_xreg(THR, reinterpret_cast<uintx_t>(thread));
+#if defined(DART_TARGET_OS_FUCHSIA) || defined(DART_TARGET_OS_ANDROID)
+  set_xreg(GP, thread->saved_shadow_call_stack());
+#endif
   // Set the tag.
   thread->set_vm_tag(VMTag::kDartTagId);
   // Clear top exit frame.

runtime/vm/thread.h

@@ -403,6 +403,7 @@ class Thread : public ThreadState {
     saved_safestack_limit_ = limit;
   }
 #endif
+  uword saved_shadow_call_stack() const { return saved_shadow_call_stack_; }
   static uword saved_shadow_call_stack_offset() {
     return OFFSET_OF(Thread, saved_shadow_call_stack_);
   }