IRGen: handle ASAN better with importing on ELF

ELF's lack of linker directives is worked around by a custom section
(`.swift1_autolink_entries`).  This is metadata that is not intended to
be emitted into the linked binary.  A previous change introduced the use
of a module (global) assembly gadget to discard the section.  However,
this interacts poorly with ASAN which would instrument the section,
resulting in a strong reference.  This reference would persist to a
discarded symbol.  lld would object to this.  Blacklist the symbol to
ensure that ASAN + autolinking can co-exist.

Author: compnerd

lib/IRGen/IRGenModule.cpp

@@ -50,6 +50,7 @@
 #include "llvm/Support/MD5.h"
 
 #include "ConformanceDescription.h"
+#include "GenDecl.h"
 #include "GenEnum.h"
 #include "GenIntegerLiteral.h"
 #include "GenType.h"
@@ -1190,6 +1191,7 @@ void IRGenModule::emitAutolinkInfo() {
     var->setSection(".swift1_autolink_entries");
     var->setAlignment(getPointerAlignment().getValue());
 
+    disableAddressSanitizer(*this, var);
     addUsedGlobal(var);
   }
 

test/IRGen/ELF-remove-autolink-section.swift

@@ -13,5 +13,15 @@
 print("Hi from Swift!")
 
 // ELF: module asm ".section .swift1_autolink_entries,\220x80000000\22"
+
+// Find the metadata entry for the blacklisting of the metadata symbol
+// Ensure that it is in the ASAN metadata
+
+// ELF-DAG: !llvm.asan.globals = !{
+// ELF-SAME: [[MD:![0-9]+]]
+// ELF-SAME: }
+
+// ELF-DAG: [[MD]] = !{[37 x i8]* @_swift1_autolink_entries, null, null, i1 false, i1 true}
+
 // SECTION: .swift1_autolink_entries
 // NOSECTION-NOT: .swift1_autolink_entries