Don't implicitly dereference DW_CFA_def_cfa_expression.

The specification isn't entirely clear. Follow the gdb interpretation.

Bug: 73954823
Test: libunwindstack_test
Change-Id: If72717f54eed84e442f43af19e615143a9796b68
(cherry picked from commit 3692f251990ecb063bb9a3f8af1f820782be9973)

4 files changed, 13 insertions, 18 deletions

diff --git a/libunwindstack/DwarfCfa.cpp b/libunwindstack/DwarfCfa.cpp
index 4fc95c766..aa8cd3a6f 100644
--- a/libunwindstack/DwarfCfa.cpp
+++ b/libunwindstack/DwarfCfa.cpp
@@ -424,7 +424,10 @@ bool DwarfCfa<AddressType>::cfa_def_cfa_offset(dwarf_loc_regs_t* loc_regs) {
 
 template <typename AddressType>
 bool DwarfCfa<AddressType>::cfa_def_cfa_expression(dwarf_loc_regs_t* loc_regs) {
-  (*loc_regs)[CFA_REG] = {.type = DWARF_LOCATION_EXPRESSION,
+  // There is only one type of expression for CFA evaluation and the DWARF
+  // specification is unclear whether it returns the address or the
+  // dereferenced value. GDB expects the value, so will we.
+  (*loc_regs)[CFA_REG] = {.type = DWARF_LOCATION_VAL_EXPRESSION,
                           .values = {operands_[0], memory_->cur_offset()}};
   return true;
 }
diff --git a/libunwindstack/DwarfSection.cpp b/libunwindstack/DwarfSection.cpp
index 764979863..ddbc12ef4 100644
--- a/libunwindstack/DwarfSection.cpp
+++ b/libunwindstack/DwarfSection.cpp
@@ -214,21 +214,13 @@ bool DwarfSectionImpl<AddressType>::Eval(const DwarfCie* cie, Memory* regular_me
       }
       eval_info.cfa += loc->values[1];
       break;
-    case DWARF_LOCATION_EXPRESSION:
     case DWARF_LOCATION_VAL_EXPRESSION: {
       AddressType value;
       if (!EvalExpression(*loc, regular_memory, &value, &eval_info.regs_info, nullptr)) {
         return false;
       }
-      if (loc->type == DWARF_LOCATION_EXPRESSION) {
-        if (!regular_memory->ReadFully(value, &eval_info.cfa, sizeof(AddressType))) {
-          last_error_.code = DWARF_ERROR_MEMORY_INVALID;
-          last_error_.address = value;
-          return false;
-        }
-      } else {
-        eval_info.cfa = value;
-      }
+      // There is only one type of valid expression for CFA evaluation.
+      eval_info.cfa = value;
       break;
     }
     default:
diff --git a/libunwindstack/tests/DwarfCfaTest.cpp b/libunwindstack/tests/DwarfCfaTest.cpp
index 68dc30cd9..7395b04dd 100644
--- a/libunwindstack/tests/DwarfCfaTest.cpp
+++ b/libunwindstack/tests/DwarfCfaTest.cpp
@@ -737,6 +737,8 @@ TYPED_TEST_P(DwarfCfaTest, cfa_def_cfa_expression) {
   ASSERT_TRUE(this->cfa_->GetLocationInfo(this->fde_.pc_start, 0x200, 0x284, &loc_regs));
   ASSERT_EQ(0x284U, this->dmem_->cur_offset());
   ASSERT_EQ(1U, loc_regs.size());
+  ASSERT_EQ(DWARF_LOCATION_VAL_EXPRESSION, loc_regs[CFA_REG].type);
+  ASSERT_EQ(0x81U, loc_regs[CFA_REG].values[0]);
 
   ASSERT_EQ("", GetFakeLogPrint());
   ASSERT_EQ("", GetFakeLogBuf());
diff --git a/libunwindstack/tests/DwarfSectionImplTest.cpp b/libunwindstack/tests/DwarfSectionImplTest.cpp
index 37305b26b..99f4d873f 100644
--- a/libunwindstack/tests/DwarfSectionImplTest.cpp
+++ b/libunwindstack/tests/DwarfSectionImplTest.cpp
@@ -99,7 +99,7 @@ TYPED_TEST_P(DwarfSectionImplTest, Eval_cfa_expr_eval_fail) {
   regs.set_sp(0x2000);
   regs[5] = 0x20;
   regs[9] = 0x3000;
-  loc_regs[CFA_REG] = DwarfLocation{DWARF_LOCATION_EXPRESSION, {0x2, 0x5002}};
+  loc_regs[CFA_REG] = DwarfLocation{DWARF_LOCATION_VAL_EXPRESSION, {0x2, 0x5002}};
   bool finished;
   ASSERT_FALSE(this->section_->Eval(&cie, &this->memory_, loc_regs, &regs, &finished));
   EXPECT_EQ(DWARF_ERROR_MEMORY_INVALID, this->section_->LastErrorCode());
@@ -116,7 +116,7 @@ TYPED_TEST_P(DwarfSectionImplTest, Eval_cfa_expr_no_stack) {
   regs[5] = 0x20;
   regs[9] = 0x3000;
   this->memory_.SetMemory(0x5000, std::vector<uint8_t>{0x96, 0x96, 0x96});
-  loc_regs[CFA_REG] = DwarfLocation{DWARF_LOCATION_EXPRESSION, {0x2, 0x5002}};
+  loc_regs[CFA_REG] = DwarfLocation{DWARF_LOCATION_VAL_EXPRESSION, {0x2, 0x5002}};
   bool finished;
   ASSERT_FALSE(this->section_->Eval(&cie, &this->memory_, loc_regs, &regs, &finished));
   EXPECT_EQ(DWARF_ERROR_ILLEGAL_STATE, this->section_->LastErrorCode());
@@ -136,10 +136,8 @@ TYPED_TEST_P(DwarfSectionImplTest, Eval_cfa_expr) {
   this->memory_.SetMemory(0x80000000, &cfa_value, sizeof(cfa_value));
   loc_regs[CFA_REG] = DwarfLocation{DWARF_LOCATION_EXPRESSION, {0x4, 0x5004}};
   bool finished;
-  ASSERT_TRUE(this->section_->Eval(&cie, &this->memory_, loc_regs, &regs, &finished));
-  EXPECT_FALSE(finished);
-  EXPECT_EQ(0x12345U, regs.sp());
-  EXPECT_EQ(0x20U, regs.pc());
+  ASSERT_FALSE(this->section_->Eval(&cie, &this->memory_, loc_regs, &regs, &finished));
+  EXPECT_EQ(DWARF_ERROR_ILLEGAL_VALUE, this->section_->LastErrorCode());
 }
 
 TYPED_TEST_P(DwarfSectionImplTest, Eval_cfa_val_expr) {
@@ -170,7 +168,7 @@ TYPED_TEST_P(DwarfSectionImplTest, Eval_cfa_expr_is_register) {
   regs[5] = 0x20;
   regs[9] = 0x3000;
   this->memory_.SetMemory(0x5000, std::vector<uint8_t>{0x50, 0x96, 0x96});
-  loc_regs[CFA_REG] = DwarfLocation{DWARF_LOCATION_EXPRESSION, {0x2, 0x5002}};
+  loc_regs[CFA_REG] = DwarfLocation{DWARF_LOCATION_VAL_EXPRESSION, {0x2, 0x5002}};
   bool finished;
   ASSERT_FALSE(this->section_->Eval(&cie, &this->memory_, loc_regs, &regs, &finished));
   EXPECT_EQ(DWARF_ERROR_NOT_IMPLEMENTED, this->section_->LastErrorCode());