[BOLT] Validate secondary entry point

bolt/include/bolt/Core/BinaryFunction.h

@@ -1174,6 +1174,11 @@ class BinaryFunction {
     return getSecondaryEntryPointSymbol(BB.getLabel());
   }
 
+  /// Remove a label from the secondary entry point map.
+  void removeSymbolFromSecondaryEntryPointMap(const MCSymbol *Label) {
+    SecondaryEntryPoints.erase(Label);
+  }
+
   /// Return true if the basic block is an entry point into the function
   /// (either primary or secondary).
   bool isEntryPoint(const BinaryBasicBlock &BB) const {
@@ -2126,6 +2131,10 @@ class BinaryFunction {
     return Islands && !Islands->DataOffsets.empty();
   }
 
+  bool isStartOfConstantIsland(uint64_t Offset) const {
+    return hasConstantIsland() && Islands->DataOffsets.count(Offset);
+  }
+
   /// Return true iff the symbol could be seen inside this function otherwise
   /// it is probably another function.
   bool isSymbolValidInScope(const SymbolRef &Symbol, uint64_t SymbolSize) const;

bolt/lib/Core/BinaryFunction.cpp

@@ -1896,6 +1896,15 @@ void BinaryFunction::postProcessEntryPoints() {
     if (BC.isAArch64() && Offset == getSize())
       continue;
 
+    // If we have grabbed a wrong code label which actually points to some
+    // constant island inside the function, ignore this label and remove it
+    // from the secondary entry point map.
+    if (isStartOfConstantIsland(Offset)) {
+      BC.SymbolToFunctionMap.erase(Label);
+      removeSymbolFromSecondaryEntryPointMap(Label);
+      continue;
+    }
+
     BC.errs() << "BOLT-WARNING: reference in the middle of instruction "
                  "detected in function "
               << *this << " at offset 0x" << Twine::utohexstr(Offset) << '\n';

bolt/test/AArch64/validate-secondary-entry-point.s

@@ -0,0 +1,34 @@
+# This test is to verify that BOLT won't take a label pointing to constant
+# island as a secondary entry point (function `_start` doesn't have ELF size
+# set originally) and the function won't otherwise be mistaken as non-simple.
+
+# RUN: %clang %cflags -pie %s -o %t.so -Wl,-q -Wl,--init=_foo -Wl,--fini=_foo
+# RUN: llvm-bolt %t.so -o %t.bolt.so --print-cfg 2>&1 | FileCheck %s
+# CHECK-NOT: BOLT-WARNING: reference in the middle of instruction detected \
+# CHECK-NOT:   function _start at offset 0x{{[0-9a-f]+}}
+# CHECK: Binary Function "_start" after building cfg
+
+  .text
+
+  .global _foo
+  .type _foo, %function
+_foo:
+  ret
+
+  .global _start
+  .type _start, %function
+_start:
+  b _foo
+
+  .balign 16
+_random_consts:
+  .long 0x12345678
+  .long 0x90abcdef
+
+  .global _bar
+  .type _bar, %function
+_bar:
+  ret
+
+  # Dummy relocation to force relocation mode
+  .reloc 0, R_AARCH64_NONE

bolt/test/RISCV/validate-secondary-entry-point.s

@@ -0,0 +1,34 @@
+# This test is to verify that BOLT won't take a label pointing to constant
+# island as a secondary entry point (function `_start` doesn't have ELF size
+# set originally) and the function won't otherwise be mistaken as non-simple.
+
+# RUN: %clang %cflags -pie %s -o %t.so -Wl,-q -Wl,--init=_foo -Wl,--fini=_foo
+# RUN: llvm-bolt %t.so -o %t.bolt.so --print-cfg 2>&1 | FileCheck %s
+# CHECK-NOT: BOLT-WARNING: reference in the middle of instruction detected \
+# CHECK-NOT:   function _start at offset 0x{{[0-9a-f]+}}
+# CHECK: Binary Function "_start" after building cfg
+
+  .text
+
+  .global _foo
+  .type _foo, %function
+_foo:
+  ret
+
+  .global _start
+  .type _start, %function
+_start:
+  j _foo
+
+  .balign 16
+_random_consts:
+  .long 0x12345678
+  .long 0x90abcdef
+
+  .global _bar
+  .type _bar, %function
+_bar:
+  ret
+
+  # Dummy relocation to force relocation mode
+  .reloc 0, R_RISCV_NONE