Merge pull request swiftlang#9403 from felipepiovezan/felipe/entry_val_as_cfa

[lldb][swift] Evaluate entry_value(async_reg) in terms of CFA

Author: felipepiovezan

lldb/source/Expression/DWARFExpression.cpp

@@ -533,6 +533,74 @@ bool DWARFExpression::LinkThreadLocalStorage(
   return true;
 }
 
+/// Returns true if \c opcodes contains the opcode for the register used for the
+/// Swift Async Context (x22 for aarch64, r14 for x86-64). It must also not
+/// contain any other opcodes.
+static bool IsAsyncRegCtxExpr(DataExtractor &opcodes,
+                              llvm::Triple::ArchType triple) {
+  offset_t offset = 0;
+  const uint8_t op_async_ctx_reg = opcodes.GetU8(&offset);
+  if (opcodes.BytesLeft(offset) != 0)
+    return false;
+
+  // FIXME: could this be exposed through the ABI/Language plugins?
+  return (triple == llvm::Triple::x86_64 && op_async_ctx_reg == DW_OP_reg14) ||
+         (triple == llvm::Triple::aarch64 && op_async_ctx_reg == DW_OP_reg22);
+}
+
+/// If \c opcodes contain the location of asynchronous contexts in Swift,
+/// evaluates DW_OP_call_frame_cfa, returns its result, and updates
+/// \c current_offset. Otherwise, does nothing. This is possible because, for
+/// async frames, the language unwinder treats the asynchronous context as the
+/// CFA of the frame.
+static llvm::Expected<Value> SwiftAsyncEvaluate_DW_OP_entry_value(
+    ExecutionContext &exe_ctx, StackFrame &current_frame,
+    const DWARFUnit *dwarf_cu, Function &func, const DataExtractor &opcodes,
+    offset_t &current_offset) {
+  auto func_name = func.GetMangled().GetMangledName();
+  if (!SwiftLanguageRuntime::IsAnySwiftAsyncFunctionSymbol(func_name))
+    return llvm::createStringError(
+        "SwiftAsyncEvaluate_DW_OP_entry_value: not an async function");
+
+  offset_t new_offset = current_offset;
+  const uint32_t subexpr_len = opcodes.GetULEB128(&new_offset);
+  const void *subexpr_data = opcodes.GetData(&new_offset, subexpr_len);
+  if (!subexpr_data)
+    return llvm::createStringError(
+        "SwiftAsyncEvaluate_DW_OP_entry_value: failed to extract subexpr");
+
+  DataExtractor subexpr_extractor(
+      subexpr_data, subexpr_len, opcodes.GetByteOrder(),
+      opcodes.GetAddressByteSize(), opcodes.getTargetByteSize());
+  if (!IsAsyncRegCtxExpr(subexpr_extractor,
+                         exe_ctx.GetTargetRef().GetArchitecture().GetMachine()))
+    return llvm::createStringError("SwiftAsyncEvaluate_DW_OP_entry_value: "
+                                   "missing async context register opcode");
+
+  // Q funclets require an extra level of indirection.
+  if (SwiftLanguageRuntime::IsSwiftAsyncAwaitResumePartialFunctionSymbol(
+          func_name)) {
+    const uint8_t maybe_op_deref = opcodes.GetU8(&new_offset);
+    if (maybe_op_deref != DW_OP_deref)
+      return llvm::createStringError("SwiftAsyncEvaluate_DW_OP_entry_value: "
+                                     "missing DW_OP_deref in Q funclet");
+  }
+
+  static const uint8_t cfa_opcode = DW_OP_call_frame_cfa;
+  DataExtractor cfa_expr_data(&cfa_opcode, 1, opcodes.GetByteOrder(),
+                              opcodes.GetAddressByteSize(),
+                              opcodes.getTargetByteSize());
+  DWARFExpressionList cfa_expr(func.CalculateSymbolContextModule(),
+                               cfa_expr_data, dwarf_cu);
+  llvm::Expected<Value> maybe_result = cfa_expr.Evaluate(
+      &exe_ctx, current_frame.GetRegisterContext().get(), LLDB_INVALID_ADDRESS,
+      /*initial_value_ptr=*/nullptr,
+      /*object_address_ptr=*/nullptr);
+  if (maybe_result)
+    current_offset = new_offset;
+  return maybe_result;
+}
+
 static llvm::Error
 Evaluate_DW_OP_entry_value(std::vector<Value> &stack, const DWARFUnit *dwarf_cu,
                            ExecutionContext *exe_ctx, RegisterContext *reg_ctx,
@@ -630,20 +698,19 @@ Evaluate_DW_OP_entry_value(std::vector<Value> &stack, const DWARFUnit *dwarf_cu,
   if (!current_func)
     return llvm::createStringError("no current function");
 
+  if (llvm::Expected<Value> result = SwiftAsyncEvaluate_DW_OP_entry_value(
+          *exe_ctx, *current_frame, dwarf_cu, *current_func, opcodes,
+          opcode_offset)) {
+    stack.push_back(*result);
+    return llvm::Error::success();
+  } else
+    LLDB_LOG_ERROR(log, result.takeError(), "{0}");
+
   CallEdge *call_edge = nullptr;
   ModuleList &modlist = target.GetImages();
   ExecutionContext parent_exe_ctx = *exe_ctx;
   parent_exe_ctx.SetFrameSP(parent_frame);
   Function *parent_func = nullptr;
-#ifdef LLDB_ENABLE_SWIFT
-  // Swift async function arguments are represented relative to a
-  // DW_OP_entry_value that fetches the async context register. This
-  // register is known to the unwinder and can always be restored
-  // therefore it is not necessary to match up a call site parameter
-  // with it.
-  auto fn_name = current_func->GetMangled().GetMangledName().GetStringRef();
-  if (!SwiftLanguageRuntime::IsAnySwiftAsyncFunctionSymbol(fn_name)) {
-#endif
 
   parent_func =
     parent_frame->GetSymbolContext(eSymbolContextFunction).function;
@@ -678,25 +745,16 @@ Evaluate_DW_OP_entry_value(std::vector<Value> &stack, const DWARFUnit *dwarf_cu,
   if (!call_edge)
     return llvm::createStringError("no unambiguous edge from parent "
                                    "to current function");
-#ifdef LLDB_ENABLE_SWIFT
-  }
-#endif
 
   // 3. Attempt to locate the DW_OP_entry_value expression in the set of
   //    available call site parameters. If found, evaluate the corresponding
   //    parameter in the context of the parent frame.
   const uint32_t subexpr_len = opcodes.GetULEB128(&opcode_offset);
-#ifdef LLDB_ENABLE_SWIFT
-  lldb::offset_t subexpr_offset = opcode_offset;
-#endif
   const void *subexpr_data = opcodes.GetData(&opcode_offset, subexpr_len);
   if (!subexpr_data)
     return llvm::createStringError("subexpr could not be read");
 
   const CallSiteParameter *matched_param = nullptr;
-#ifdef LLDB_ENABLE_SWIFT
-  if (call_edge) {
-#endif
   for (const CallSiteParameter &param : call_edge->GetCallSiteParameters()) {
     DataExtractor param_subexpr_extractor;
     if (!param.LocationInCallee.GetExpressionData(param_subexpr_extractor))
@@ -722,25 +780,10 @@ Evaluate_DW_OP_entry_value(std::vector<Value> &stack, const DWARFUnit *dwarf_cu,
   }
   if (!matched_param)
     return llvm::createStringError("no matching call site param found");
-#ifdef LLDB_ENABLE_SWIFT
-  }
-  std::optional<DWARFExpressionList> subexpr;
-  if (!matched_param) {
-    auto *ctx_func = parent_func ? parent_func : current_func;
-    subexpr.emplace(ctx_func->CalculateSymbolContextModule(),
-                    DataExtractor(opcodes, subexpr_offset, subexpr_len),
-                    dwarf_cu);
-  }
-#endif
 
   // TODO: Add support for DW_OP_push_object_address within a DW_OP_entry_value
   // subexpresion whenever llvm does.
-#ifdef LLDB_ENABLE_SWIFT
-  const DWARFExpressionList &param_expr =
-      matched_param ? matched_param->LocationInCaller : *subexpr;
-#else
   const DWARFExpressionList &param_expr = matched_param->LocationInCaller;
-#endif
 
   llvm::Expected<Value> maybe_result = param_expr.Evaluate(
       &parent_exe_ctx, parent_frame->GetRegisterContext().get(),

lldb/source/Plugins/LanguageRuntime/Swift/SwiftLanguageRuntime.cpp

@@ -2538,11 +2538,6 @@ struct AsyncUnwindRegisterNumbers {
   uint32_t async_ctx_regnum;
   uint32_t fp_regnum;
   uint32_t pc_regnum;
-  /// A register to use as a marker to indicate how the async context is passed
-  /// to the function (indirectly, or not). This needs to be communicated to the
-  /// frames below us as they need to react differently. There is no good way to
-  /// expose this, so we set another dummy register to communicate this state.
-  uint32_t dummy_regnum;
 
   RegisterKind GetRegisterKind() const { return lldb::eRegisterKindDWARF; }
 };
@@ -2556,15 +2551,13 @@ GetAsyncUnwindRegisterNumbers(llvm::Triple::ArchType triple) {
     regnums.async_ctx_regnum = dwarf_r14_x86_64;
     regnums.fp_regnum = dwarf_rbp_x86_64;
     regnums.pc_regnum = dwarf_rip_x86_64;
-    regnums.dummy_regnum = dwarf_r15_x86_64;
     return regnums;
   }
   case llvm::Triple::aarch64: {
     AsyncUnwindRegisterNumbers regnums;
     regnums.async_ctx_regnum = arm64_dwarf::x22;
     regnums.fp_regnum = arm64_dwarf::fp;
     regnums.pc_regnum = arm64_dwarf::pc;
-    regnums.dummy_regnum = arm64_dwarf::x23;
     return regnums;
   }
   default:
@@ -2810,18 +2803,11 @@ SwiftLanguageRuntime::GetRuntimeUnwindPlan(ProcessSP process_sp,
   // The CFA of a funclet is its own async context.
   row->GetCFAValue().SetIsConstant(*async_ctx);
 
-  // The value of the async register in the parent frame is the entry value of
-  // the async register in the current frame. This mimics a function call, as
-  // if the parent funclet had called the current funclet.
-  row->SetRegisterLocationToIsConstant(regnums->async_ctx_regnum, *async_reg,
+  // The value of the async register in the parent frame (which is the
+  // continuation funclet) is the async context of this frame.
+  row->SetRegisterLocationToIsConstant(regnums->async_ctx_regnum, *async_ctx,
                                        /*can_replace=*/false);
 
-  // The parent frame needs to know how to interpret the value it is given for
-  // its own async register. A dummy register is used to communicate that.
-  if (!indirect_context)
-    row->SetRegisterLocationToIsConstant(regnums->dummy_regnum, 0,
-                                         /*can_replace=*/false);
-
   if (std::optional<addr_t> pc_after_prologue =
           TrySkipVirtualParentProlog(*async_ctx, *process_sp))
     row->SetRegisterLocationToIsConstant(regnums->pc_regnum, *pc_after_prologue,
@@ -2854,59 +2840,13 @@ UnwindPlanSP SwiftLanguageRuntime::GetFollowAsyncContextUnwindPlan(
   if (!regnums)
     return UnwindPlanSP();
 
-  const bool is_indirect =
-      regctx->ReadRegisterAsUnsigned(regnums->dummy_regnum, (uint64_t)-1ll) ==
-      (uint64_t)-1ll;
-  // In the general case, the async register setup by the frame above us
-  // should be dereferenced twice to get our context, except when the frame
-  // above us is an async frame on the OS stack that takes its context directly
-  // (see discussion in GetRuntimeUnwindPlan()). The availability of
-  // dummy_regnum is used as a marker for this situation.
-  if (!is_indirect) {
-    row->GetCFAValue().SetIsRegisterDereferenced(regnums->async_ctx_regnum);
-    row->SetRegisterLocationToSame(regnums->async_ctx_regnum, false);
-  } else {
-    static const uint8_t async_dwarf_expression_x86_64[] = {
-        llvm::dwarf::DW_OP_regx, dwarf_r14_x86_64, // DW_OP_regx, reg
-        llvm::dwarf::DW_OP_deref,                  // DW_OP_deref
-        llvm::dwarf::DW_OP_deref,                  // DW_OP_deref
-    };
-    static const uint8_t async_dwarf_expression_arm64[] = {
-        llvm::dwarf::DW_OP_regx, arm64_dwarf::x22, // DW_OP_regx, reg
-        llvm::dwarf::DW_OP_deref,                  // DW_OP_deref
-        llvm::dwarf::DW_OP_deref,                  // DW_OP_deref
-    };
-
-    const unsigned expr_size = sizeof(async_dwarf_expression_x86_64);
-    static_assert(sizeof(async_dwarf_expression_x86_64) ==
-                      sizeof(async_dwarf_expression_arm64),
-                  "Expressions of different sizes");
-
-    const uint8_t *expression = nullptr;
-    if (arch.GetMachine() == llvm::Triple::x86_64)
-      expression = async_dwarf_expression_x86_64;
-    else if (arch.GetMachine() == llvm::Triple::aarch64)
-      expression = async_dwarf_expression_arm64;
-    else
-      llvm_unreachable("Unsupported architecture");
-
-    // Note how the register location gets the same expression pointer with a
-    // different size. We just skip the trailing deref for it.
-    assert(expression[expr_size - 1] == llvm::dwarf::DW_OP_deref &&
-           "Should skip a deref");
-    row->GetCFAValue().SetIsDWARFExpression(expression, expr_size);
-    row->SetRegisterLocationToIsDWARFExpression(
-        regnums->async_ctx_regnum, expression, expr_size - 1, false);
-  }
-
-  // Suppose this is unwinding frame #2 of a call stack. The value given for
-  // the async register has two possible values, depending on what frame #1
-  // expects:
-  // 1. The CFA of frame #1, direct ABI, dereferencing it once produces CFA of
-  // Frame #2.
-  // 2. The CFA of frame #0, indirect ABI, dereferencing it twice produces CFA
-  // of Frame #2.
-  const unsigned num_indirections = 1 + is_indirect;
+  row->GetCFAValue().SetIsRegisterDereferenced(regnums->async_ctx_regnum);
+  // The value of the async register in the parent frame (which is the
+  // continuation funclet) is the async context of this frame.
+  row->SetRegisterLocationToIsCFAPlusOffset(regnums->async_ctx_regnum,
+                                            /*offset*/ 0, false);
+
+  const unsigned num_indirections = 1;
   if (std::optional<addr_t> pc_after_prologue = TrySkipVirtualParentProlog(
           GetAsyncContext(regctx), *process_sp, num_indirections))
     row->SetRegisterLocationToIsConstant(regnums->pc_regnum, *pc_after_prologue,

lldb/test/API/lang/swift/async/frame/variables_multiple_frames/TestSwiftAsyncFrameVarMultipleFrames.py

@@ -4,42 +4,63 @@
 import lldbsuite.test.lldbutil as lldbutil
 
 
+@skipIf(archs=no_match(["arm64", "arm64e", "x86_64"]))
 class TestCase(lldbtest.TestBase):
 
     mydir = lldbtest.TestBase.compute_mydir(__file__)
 
+    def read_ptr_from_memory(self, process, addr):
+        error = lldb.SBError()
+        value = process.ReadPointerFromMemory(addr, error)
+        self.assertSuccess(error, "Failed to read memory")
+        return value
+
     # Check that the CFA chain is correctly built
     def check_cfas(self, async_frames, process):
         async_cfas = list(map(lambda frame: frame.GetCFA(), async_frames))
         expected_cfas = [async_cfas[0]]
         # The CFA chain ends in nullptr.
         while expected_cfas[-1] != 0:
-            error = lldb.SBError()
-            expected_cfas.append(
-                process.ReadPointerFromMemory(expected_cfas[-1], error)
-            )
-            self.assertSuccess(error, "Managed to read cfa memory")
+            expected_cfas.append(self.read_ptr_from_memory(process, expected_cfas[-1]))
 
         self.assertEqual(async_cfas, expected_cfas[:-1])
 
     def check_pcs(self, async_frames, process, target):
         for idx, frame in enumerate(async_frames[:-1]):
             # Read the continuation pointer from the second field of the CFA.
-            error = lldb.SBError()
-            continuation_ptr = process.ReadPointerFromMemory(
-                frame.GetCFA() + target.addr_size, error
+            continuation_ptr = self.read_ptr_from_memory(
+                process, frame.GetCFA() + target.addr_size
             )
-            self.assertSuccess(error, "Managed to read context memory")
 
             # The PC of the previous frame should be the continuation pointer
             # with the funclet's prologue skipped.
             parent_frame = async_frames[idx + 1]
             prologue_to_skip = parent_frame.GetFunction().GetPrologueByteSize()
             self.assertEqual(continuation_ptr + prologue_to_skip, parent_frame.GetPC())
 
+    def check_async_regs_one_frame(self, frame, process):
+        async_reg_name = "r14" if self.getArchitecture() == "x86_64" else "x22"
+
+        cfa = frame.GetCFA()
+        is_indirect = "await resume" in frame.GetFunctionName()
+        async_register = frame.FindRegister(async_reg_name).GetValueAsUnsigned()
+
+        if is_indirect:
+            deref_async_reg = self.read_ptr_from_memory(process, async_register)
+            self.assertEqual(deref_async_reg, cfa)
+        else:
+            self.assertEqual(async_register, cfa)
+
+    def check_async_regs(self, async_frames, process):
+        for frame in async_frames:
+            # The frames from the implicit main function don't have a demangled
+            # name, so we can't test whether they are a Q funclet or not.
+            if "Main" in frame.GetFunctionName():
+                break
+            self.check_async_regs_one_frame(frame, process)
 
     def check_variables(self, async_frames, expected_values):
-        for (frame, expected_value) in zip(async_frames, expected_values):
+        for frame, expected_value in zip(async_frames, expected_values):
             myvar = frame.FindVariable("myvar")
             lldbutil.check_variable(self, myvar, False, value=expected_value)
 
@@ -58,6 +79,7 @@ def test(self):
         self.check_cfas(async_frames, process)
         self.check_pcs(async_frames, process, target)
         self.check_variables(async_frames, ["222", "333", "444", "555"])
+        self.check_async_regs(async_frames, process)
 
         target.DeleteAllBreakpoints()
         target.BreakpointCreateBySourceRegex("breakpoint2", source_file)
@@ -68,6 +90,7 @@ def test(self):
         self.check_cfas(async_frames, process)
         self.check_pcs(async_frames, process, target)
         self.check_variables(async_frames, ["111", "222", "333", "444", "555"])
+        self.check_async_regs(async_frames, process)
 
         # Now stop at the Q funclet right after the await to ASYNC___1
         target.DeleteAllBreakpoints()
@@ -77,6 +100,7 @@ def test(self):
         self.check_cfas(async_frames, process)
         self.check_pcs(async_frames, process, target)
         self.check_variables(async_frames, ["222", "333", "444", "555"])
+        self.check_async_regs(async_frames, process)
 
         target.DeleteAllBreakpoints()
         target.BreakpointCreateBySourceRegex("breakpoint3", source_file)
@@ -85,3 +109,4 @@ def test(self):
         self.check_cfas(async_frames, process)
         self.check_pcs(async_frames, process, target)
         self.check_variables(async_frames, ["222", "333", "444", "555"])
+        self.check_async_regs(async_frames, process)