Use dyn_cast instead of static_cast.

Now that MachoFile has classof(), we can use dyn_cast instead which
is actually the only safe way to handle this.

Turns out this actually manifests as a bug as we were incorrectly
casting instances which weren't MachoFile in to a MachoFile.

Unfortunately, there's no reliable way of checking for this as it
requires that the file we are looking for has a 0 at exactly the byte
we need for the load of subsectionsViaSymbols.

llvm-svn: 259413

diff --git a/lld/lib/ReaderWriter/MachO/MachONormalizedFileFromAtoms.cpp b/lld/lib/ReaderWriter/MachO/MachONormalizedFileFromAtoms.cpp
index 122b540..22cdede 100644 (file)
--- a/lld/lib/ReaderWriter/MachO/MachONormalizedFileFromAtoms.cpp
+++ b/lld/lib/ReaderWriter/MachO/MachONormalizedFileFromAtoms.cpp
@@ -377,11 +377,11 @@ void Util::processDefinedAtoms(const lld::File &atomFile) {
 }
 
 void Util::processAtomAttributes(const DefinedAtom *atom) {
-  auto *machoFile = static_cast<const mach_o::MachOFile *>(&atom->file());
   // If the file doesn't use subsections via symbols, then make sure we don't
   // add that flag to the final output file if we have a relocatable file.
-  if (!machoFile->subsectionsViaSymbols())
-    _subsectionsViaSymbols = false;
+  if (auto *machoFile = dyn_cast<mach_o::MachOFile>(&atom->file()))
+    if (!machoFile->subsectionsViaSymbols())
+      _subsectionsViaSymbols = false;
 }
 
 void Util::assignAtomToSection(const DefinedAtom *atom) {