[JITLink][MachO] Handle intra-block subtractor relocations.

Previously the JITLink MachO backends (aarch64 and x86-64) only looked at the
fixup block to determine which symbol was being fixed up. This assumption breaks
if both symbols used in the subtractor are in the same block. The fix is to
check for such cases and use the offsets of each symbol to decide which is being
fixed up.

The issue only resulted in incorrect behavior for negative-delta relocations,
so the testcases use eh-frames with explicit edges for the CIE-pointer field in
FDEs (since these are negative-deltas).

rdar://119351329

Author: lhames

llvm/lib/ExecutionEngine/JITLink/MachO_arm64.cpp

@@ -188,21 +188,41 @@ class MachOLinkGraphBuilder_arm64 : public MachOLinkGraphBuilder {
     Edge::Kind DeltaKind;
     Symbol *TargetSymbol;
     uint64_t Addend;
+
+    bool FixingFromSymbol = true;
     if (&BlockToFix == &FromSymbol->getAddressable()) {
+      if (LLVM_UNLIKELY(&BlockToFix == &ToSymbol->getAddressable())) {
+        // From and To are symbols in the same block. Decide direction by offset
+        // instead.
+        if (ToSymbol->getAddress() > FixupAddress)
+          FixingFromSymbol = true;
+        else if (FromSymbol->getAddress() > FixupAddress)
+          FixingFromSymbol = false;
+        else
+          FixingFromSymbol = FromSymbol->getAddress() >= ToSymbol->getAddress();
+      } else
+        FixingFromSymbol = true;
+    } else {
+      if (&BlockToFix == &ToSymbol->getAddressable())
+        FixingFromSymbol = false;
+      else {
+        // BlockToFix was neither FromSymbol nor ToSymbol.
+        return make_error<JITLinkError>("SUBTRACTOR relocation must fix up "
+                                        "either 'A' or 'B' (or a symbol in one "
+                                        "of their alt-entry groups)");
+      }
+    }
+
+    if (FixingFromSymbol) {
       TargetSymbol = ToSymbol;
       DeltaKind = (SubRI.r_length == 3) ? aarch64::Delta64 : aarch64::Delta32;
       Addend = FixupValue + (FixupAddress - FromSymbol->getAddress());
       // FIXME: handle extern 'from'.
-    } else if (&BlockToFix == &ToSymbol->getAddressable()) {
+    } else {
       TargetSymbol = &*FromSymbol;
       DeltaKind =
           (SubRI.r_length == 3) ? aarch64::NegDelta64 : aarch64::NegDelta32;
       Addend = FixupValue - (FixupAddress - ToSymbol->getAddress());
-    } else {
-      // BlockToFix was neither FromSymbol nor ToSymbol.
-      return make_error<JITLinkError>("SUBTRACTOR relocation must fix up "
-                                      "either 'A' or 'B' (or a symbol in one "
-                                      "of their alt-entry groups)");
     }
 
     return PairRelocInfo(DeltaKind, TargetSymbol, Addend);

llvm/lib/ExecutionEngine/JITLink/MachO_x86_64.cpp

@@ -179,21 +179,41 @@ class MachOLinkGraphBuilder_x86_64 : public MachOLinkGraphBuilder {
     Edge::Kind DeltaKind;
     Symbol *TargetSymbol;
     uint64_t Addend;
+
+    bool FixingFromSymbol = true;
     if (&BlockToFix == &FromSymbol->getAddressable()) {
+      if (LLVM_UNLIKELY(&BlockToFix == &ToSymbol->getAddressable())) {
+        // From and To are symbols in the same block. Decide direction by offset
+        // instead.
+        if (ToSymbol->getAddress() > FixupAddress)
+          FixingFromSymbol = true;
+        else if (FromSymbol->getAddress() > FixupAddress)
+          FixingFromSymbol = false;
+        else
+          FixingFromSymbol = FromSymbol->getAddress() >= ToSymbol->getAddress();
+      } else
+        FixingFromSymbol = true;
+    } else {
+      if (&BlockToFix == &ToSymbol->getAddressable())
+        FixingFromSymbol = false;
+      else {
+        // BlockToFix was neither FromSymbol nor ToSymbol.
+        return make_error<JITLinkError>("SUBTRACTOR relocation must fix up "
+                                        "either 'A' or 'B' (or a symbol in one "
+                                        "of their alt-entry groups)");
+      }
+    }
+
+    if (FixingFromSymbol) {
       TargetSymbol = ToSymbol;
       DeltaKind = (SubRI.r_length == 3) ? x86_64::Delta64 : x86_64::Delta32;
       Addend = FixupValue + (FixupAddress - FromSymbol->getAddress());
       // FIXME: handle extern 'from'.
-    } else if (&BlockToFix == &ToSymbol->getAddressable()) {
+    } else {
       TargetSymbol = FromSymbol;
       DeltaKind =
           (SubRI.r_length == 3) ? x86_64::NegDelta64 : x86_64::NegDelta32;
       Addend = FixupValue - (FixupAddress - ToSymbol->getAddress());
-    } else {
-      // BlockToFix was neither FromSymbol nor ToSymbol.
-      return make_error<JITLinkError>("SUBTRACTOR relocation must fix up "
-                                      "either 'A' or 'B' (or a symbol in one "
-                                      "of their alt-entry chains)");
     }
 
     return PairRelocInfo(DeltaKind, TargetSymbol, Addend);