Remove undefined behaviour in add/sub immediate

The macro assembler support for add/sub immediate could attempt to negate the
minimum int64_t value, which is undefined behaviour. Check the value before
negation.

Change-Id: If5c12515fbef490318a90930e7a362876b0e6dc5

1 files changed, 16 insertions, 10 deletions

diff --git a/src/aarch64/macro-assembler-aarch64.cc b/src/aarch64/macro-assembler-aarch64.cc
index 1e81a8d7..56c6eaf6 100644
--- a/src/aarch64/macro-assembler-aarch64.cc
+++ b/src/aarch64/macro-assembler-aarch64.cc
@@ -1427,12 +1427,15 @@ void MacroAssembler::Add(const Register& rd,
                          const Operand& operand,
                          FlagsUpdate S) {
   VIXL_ASSERT(allow_macro_instructions_);
-  if (operand.IsImmediate() && (operand.GetImmediate() < 0) &&
-      IsImmAddSub(-operand.GetImmediate())) {
-    AddSubMacro(rd, rn, -operand.GetImmediate(), S, SUB);
-  } else {
-    AddSubMacro(rd, rn, operand, S, ADD);
+  if (operand.IsImmediate()) {
+    int64_t imm = operand.GetImmediate();
+    if ((imm < 0) && (imm != std::numeric_limits<int64_t>::min()) &&
+        IsImmAddSub(-imm)) {
+      AddSubMacro(rd, rn, -imm, S, SUB);
+      return;
+    }
   }
+  AddSubMacro(rd, rn, operand, S, ADD);
 }
 
 
@@ -1448,12 +1451,15 @@ void MacroAssembler::Sub(const Register& rd,
                          const Operand& operand,
                          FlagsUpdate S) {
   VIXL_ASSERT(allow_macro_instructions_);
-  if (operand.IsImmediate() && (operand.GetImmediate() < 0) &&
-      IsImmAddSub(-operand.GetImmediate())) {
-    AddSubMacro(rd, rn, -operand.GetImmediate(), S, ADD);
-  } else {
-    AddSubMacro(rd, rn, operand, S, SUB);
+  if (operand.IsImmediate()) {
+    int64_t imm = operand.GetImmediate();
+    if ((imm < 0) && (imm != std::numeric_limits<int64_t>::min()) &&
+        IsImmAddSub(-imm)) {
+      AddSubMacro(rd, rn, -imm, S, ADD);
+      return;
+    }
   }
+  AddSubMacro(rd, rn, operand, S, SUB);
 }