AArch64: make RuntimeDyld relocations idempotent

AArch64 ELF uses .rela relocations so there's no need to actually make
use of the bits we're setting in the destination  However, we should
make sure all bits are cleared properly since multiple runs of
resolveRelocations are possible and these could combine to produce
invalid results if stale versions remain in the code.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@182214 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 22 insertions, 2 deletions

diff --git a/lib/ExecutionEngine/RuntimeDyld/RuntimeDyldELF.cpp b/lib/ExecutionEngine/RuntimeDyld/RuntimeDyldELF.cpp
index 2773bf1..9494e6b 100644
--- a/lib/ExecutionEngine/RuntimeDyld/RuntimeDyldELF.cpp
+++ b/lib/ExecutionEngine/RuntimeDyld/RuntimeDyldELF.cpp
@@ -277,7 +277,6 @@ void RuntimeDyldELF::resolveX86Relocation(const SectionEntry &Section,
   }
 }
 
-// FIXME: PR16013: this routine needs modification to handle repeated relocations.
 void RuntimeDyldELF::resolveAArch64Relocation(const SectionEntry &Section,
                                               uint64_t Offset,
                                               uint64_t Value,
@@ -303,7 +302,7 @@ void RuntimeDyldELF::resolveAArch64Relocation(const SectionEntry &Section,
     *TargetPtr = Value + Addend;
     break;
   }
-  case ELF::R_AARCH64_PREL32: { // test-shift.ll (.eh_frame)
+  case ELF::R_AARCH64_PREL32: {
     uint64_t Result = Value + Addend - FinalAddress;
     assert(static_cast<int64_t>(Result) >= INT32_MIN && 
            static_cast<int64_t>(Result) <= UINT32_MAX);
@@ -319,12 +318,20 @@ void RuntimeDyldELF::resolveAArch64Relocation(const SectionEntry &Section,
     // "Check that -2^27 <= result < 2^27".
     assert(-(1LL << 27) <= static_cast<int64_t>(BranchImm) && 
            static_cast<int64_t>(BranchImm) < (1LL << 27));
+
+    // AArch64 code is emitted with .rela relocations. The data already in any
+    // bits affected by the relocation on entry is garbage.
+    *TargetPtr &= 0xfc000000U;
     // Immediate goes in bits 25:0 of B and BL.
     *TargetPtr |= static_cast<uint32_t>(BranchImm & 0xffffffcU) >> 2;
     break;
   }
   case ELF::R_AARCH64_MOVW_UABS_G3: {
     uint64_t Result = Value + Addend;
+
+    // AArch64 code is emitted with .rela relocations. The data already in any
+    // bits affected by the relocation on entry is garbage.
+    *TargetPtr &= 0xff80001fU;
     // Immediate goes in bits 20:5 of MOVZ/MOVK instruction
     *TargetPtr |= Result >> (48 - 5);
     // Shift is "lsl #48", in bits 22:21
@@ -333,6 +340,11 @@ void RuntimeDyldELF::resolveAArch64Relocation(const SectionEntry &Section,
   }
   case ELF::R_AARCH64_MOVW_UABS_G2_NC: {
     uint64_t Result = Value + Addend;
+
+
+    // AArch64 code is emitted with .rela relocations. The data already in any
+    // bits affected by the relocation on entry is garbage.
+    *TargetPtr &= 0xff80001fU;
     // Immediate goes in bits 20:5 of MOVZ/MOVK instruction
     *TargetPtr |= ((Result & 0xffff00000000ULL) >> (32 - 5));
     // Shift is "lsl #32", in bits 22:21
@@ -341,6 +353,10 @@ void RuntimeDyldELF::resolveAArch64Relocation(const SectionEntry &Section,
   }
   case ELF::R_AARCH64_MOVW_UABS_G1_NC: {
     uint64_t Result = Value + Addend;
+
+    // AArch64 code is emitted with .rela relocations. The data already in any
+    // bits affected by the relocation on entry is garbage.
+    *TargetPtr &= 0xff80001fU;
     // Immediate goes in bits 20:5 of MOVZ/MOVK instruction
     *TargetPtr |= ((Result & 0xffff0000U) >> (16 - 5));
     // Shift is "lsl #16", in bits 22:21
@@ -349,6 +365,10 @@ void RuntimeDyldELF::resolveAArch64Relocation(const SectionEntry &Section,
   }
   case ELF::R_AARCH64_MOVW_UABS_G0_NC: {
     uint64_t Result = Value + Addend;
+
+    // AArch64 code is emitted with .rela relocations. The data already in any
+    // bits affected by the relocation on entry is garbage.
+    *TargetPtr &= 0xff80001fU;
     // Immediate goes in bits 20:5 of MOVZ/MOVK instruction
     *TargetPtr |= ((Result & 0xffffU) << 5);
     // Shift is "lsl #0", in bits 22:21. No action needed.