[BOLT] Check entry point address is not in constant island (llvm#163418)

There are cases where `addEntryPointAtOffset` is called with a given
`Offset` that points to an address within a constant island. This
triggers `assert(!isInConstantIsland(EntryPointAddress)` and causes BOLT
to crash. This patch adds a check which ignores functions that would add
such entry points and warns the user.

Author: Asher8118

bolt/lib/Core/BinaryContext.cpp

@@ -1337,8 +1337,17 @@ void BinaryContext::processInterproceduralReferences() {
             << Function.getPrintName() << " and "
             << TargetFunction->getPrintName() << '\n';
       }
-      if (uint64_t Offset = Address - TargetFunction->getAddress())
-        TargetFunction->addEntryPointAtOffset(Offset);
+      if (uint64_t Offset = Address - TargetFunction->getAddress()) {
+        if (!TargetFunction->isInConstantIsland(Address)) {
+          TargetFunction->addEntryPointAtOffset(Offset);
+        } else {
+          TargetFunction->setIgnored();
+          this->outs() << "BOLT-WARNING: Ignoring entry point at address 0x"
+                       << Twine::utohexstr(Address)
+                       << " in constant island of function " << *TargetFunction
+                       << '\n';
+        }
+      }
 
       continue;
     }

bolt/test/AArch64/constant-island-entry.s

@@ -0,0 +1,27 @@
+// This test checks that we ignore functions which add an entry point that
+// is in a constant island.
+
+# RUN: llvm-mc -filetype=obj -triple aarch64-unknown-unknown %s -o %t.o
+# RUN: %clang %cflags %t.o -pie -Wl,-q -o %t.exe
+# RUN: llvm-bolt %t.exe -o %t.bolt 2>&1 | FileCheck %s
+
+# CHECK: BOLT-WARNING: Ignoring entry point at address 0x{{[0-9a-f]+}} in constant island of function func
+
+.globl func
+.type func, %function
+func:
+  b .Lafter_constant
+
+.type constant_island, %object
+constant_island:
+  .xword 0xabcdef
+
+.Lafter_constant:
+  ret
+  .size func, .-func
+
+.globl caller
+.type caller, %function
+caller:
+  bl constant_island
+  ret