[AArch64][libunwind] Unwinding support for return address signing wit…

…h B Key

- Support for the case where the return address has been signed with the B key
- When the B key is used, a 'B' character is present in the augmentation string
  of CIE associated with the FDE for the function.

Differential Revision: https://reviews.llvm.org/D55704

llvm-svn: 349339

libunwind/src/DwarfInstructions.hpp

@@ -211,9 +211,13 @@ int DwarfInstructions<A, R>::stepWithDwarf(A &addressSpace, pint_t pc,
         register unsigned long long x17 __asm("x17") = returnAddress;
         register unsigned long long x16 __asm("x16") = cfa;
 
-        // This is the autia1716 instruction. The hint instruction is used here
-        // as gcc does not assemble autia1716 for pre armv8.3a targets.
-        asm("hint 0xc": "+r"(x17): "r"(x16));
+        // These are the autia1716/autib1716 instructions. The hint instructions
+        // are used here as gcc does not assemble autia1716/autib1716 for pre
+        // armv8.3a targets.
+        if (cieInfo.addressesSignedWithBKey)
+          asm("hint 0xe" : "+r"(x17) : "r"(x16)); // autib1716
+        else
+          asm("hint 0xc" : "+r"(x17) : "r"(x16)); // autia1716
         returnAddress = x17;
 #endif
       }

libunwind/src/DwarfParser.hpp

@@ -49,6 +49,9 @@ class CFI_Parser {
     bool      isSignalFrame;
     bool      fdesHaveAugmentationData;
     uint8_t   returnAddressRegister;
+#if defined(_LIBUNWIND_TARGET_AARCH64)
+    bool      addressesSignedWithBKey;
+#endif
   };
 
   /// Information about an FDE (Frame Description Entry)
@@ -263,6 +266,9 @@ const char *CFI_Parser<A>::parseCIE(A &addressSpace, pint_t cie,
   cieInfo->dataAlignFactor = 0;
   cieInfo->isSignalFrame = false;
   cieInfo->fdesHaveAugmentationData = false;
+#if defined(_LIBUNWIND_TARGET_AARCH64)
+  cieInfo->addressesSignedWithBKey = false;
+#endif
   cieInfo->cieStart = cie;
   pint_t p = cie;
   pint_t cieLength = (pint_t)addressSpace.get32(p);
@@ -326,6 +332,11 @@ const char *CFI_Parser<A>::parseCIE(A &addressSpace, pint_t cie,
       case 'S':
         cieInfo->isSignalFrame = true;
         break;
+#if defined(_LIBUNWIND_TARGET_AARCH64)
+      case 'B':
+        cieInfo->addressesSignedWithBKey = true;
+        break;
+#endif
       default:
         // ignore unknown letters
         break;