[AArch64][libunwind] Unwinding support for return address signing with B Key

[LukeCheeseman]

Summary

• 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.

[olista01]

LGTM with one nit.

src/DwarfInstructions.hpp

214

Comment needs updating to also mention AUTIB1716.

src/DwarfInstructions.hpp

#if defined(_LIBUNWIND_TARGET_AARCH64)
       // to a NOP on pre-v8.3a architectures.
       if (prolog.savedRegisters[UNW_ARM64_RA_SIGN_STATE].value) {
 #if !defined(_LIBUNWIND_IS_NATIVE_ONLY)
         return UNW_ECROSSRASIGNING;
 #else
         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.
+        if (cieInfo.addressesSignedWithBKey)
+          asm("hint 0xe": "+r"(x17): "r"(x16));
+        else
           asm("hint 0xc": "+r"(x17): "r"(x16));
         returnAddress = x17;
 #endif
       }
 #endif
 
       // Return address is address after call site instruction, so setting IP to
       // that does simualates a return.
       newRegisters.setIP(returnAddress);

src/DwarfParser.hpp

struct CIE_Info {
     uint8_t   personalityEncoding;
     uint8_t   personalityOffsetInCIE;
     pint_t    personality;
     uint32_t  codeAlignFactor;
     int       dataAlignFactor;
     bool      isSignalFrame;
     bool      fdesHaveAugmentationData;
     uint8_t   returnAddressRegister;
+#if defined(_LIBUNWIND_TARGET_AARCH64)
+    bool      addressesSignedWithBKey;
+#endif
   };
 
   /// Information about an FDE (Frame Description Entry)
   struct FDE_Info {
     pint_t  fdeStart;
     pint_t  fdeLength;
     pint_t  fdeInstructions;
     pint_t  pcStart;
const char *CFI_Parser<A>::parseCIE(A &addressSpace, pint_t cie,
   cieInfo->lsdaEncoding = DW_EH_PE_omit;
   cieInfo->personalityEncoding = 0;
   cieInfo->personalityOffsetInCIE = 0;
   cieInfo->personality = 0;
   cieInfo->codeAlignFactor = 0;
   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);
   p += 4;
   pint_t cieContentEnd = p + cieLength;
   if (cieLength == 0xffffffff) {
     // 0xffffffff means length is really next 8 bytes
     cieLength = (pint_t)addressSpace.get64(p);
for (pint_t s = strStart; addressSpace.get8(s) != '\0'; ++s) {
         break;
       case 'R':
         cieInfo->pointerEncoding = addressSpace.get8(p);
         ++p;
         break;
       case 'S':
         cieInfo->isSignalFrame = true;
         break;
+#if defined(_LIBUNWIND_TARGET_AARCH64)
+      case 'B':
+        cieInfo->addressesSignedWithBKey = true;
+        break;
+#endif
       default:
         // ignore unknown letters
         break;
       }
     }
   }
   cieInfo->cieLength = cieContentEnd - cieInfo->cieStart;
   cieInfo->cieInstructions = p;