[hwasan] Add hwasan-all-globals option

hwasan-globals does not instrument globals with custom sections,
because existing code may use __start_/__stop_ symbols to iterate
over globals in such a way which will cause hwasan assertions.

Introduce new hwasan-all-globals option, which instruments all
user-defined globals (but not those globals which are generated by
the hwasan instrumentation itself), including those with custom sections.

Author: shuffle2

llvm/lib/Transforms/Instrumentation/HWAddressSanitizer.cpp

@@ -160,6 +160,16 @@ static cl::opt<bool> ClGenerateTagsWithCalls(
 static cl::opt<bool> ClGlobals("hwasan-globals", cl::desc("Instrument globals"),
                                cl::Hidden, cl::init(false));
 
+static cl::opt<bool> ClAllGlobals(
+    "hwasan-all-globals",
+    cl::desc(
+        "Instrument globals, even those within user-defined sections. Warning: "
+        "This may break existing code which walks globals via linker-generated "
+        "symbols, expects certain globals to be contiguous with each other, or "
+        "makes other assumptions which are invalidated by HWASan "
+        "instrumentation."),
+    cl::Hidden, cl::init(false));
+
 static cl::opt<int> ClMatchAllTag(
     "hwasan-match-all-tag",
     cl::desc("don't report bad accesses via pointers with this tag"),
@@ -452,6 +462,7 @@ class HWAddressSanitizer {
   bool InstrumentWithCalls;
   bool InstrumentStack;
   bool InstrumentGlobals;
+  bool InstrumentAllGlobals;
   bool DetectUseAfterScope;
   bool UsePageAliases;
   bool UseMatchAllCallback;
@@ -679,6 +690,7 @@ void HWAddressSanitizer::initializeModule() {
 
   InstrumentGlobals =
       !CompileKernel && !UsePageAliases && optOr(ClGlobals, NewRuntime);
+  InstrumentAllGlobals = ClAllGlobals;
 
   if (!CompileKernel) {
     createHwasanCtorComdat();
@@ -1780,11 +1792,21 @@ void HWAddressSanitizer::instrumentGlobals() {
     if (GV.hasCommonLinkage())
       continue;
 
-    // Globals with custom sections may be used in __start_/__stop_ enumeration,
-    // which would be broken both by adding tags and potentially by the extra
-    // padding/alignment that we insert.
-    if (GV.hasSection())
-      continue;
+    if (InstrumentAllGlobals) {
+      // Avoid adding metadata emitted for the hwasan instrumentation itself.
+      // Code which makes assumptions about memory layout of globals between
+      // __start_<section>/__end_<section> linker-generated symbols may need
+      // manual adaptation.
+      auto section = GV.getSection();
+      if (section == "hwasan_globals" || section == ".note.hwasan.globals")
+        continue;
+    } else {
+      // Globals with custom sections may be used in __start_/__stop_
+      // enumeration, which would be broken both by adding tags and potentially
+      // by the extra padding/alignment that we insert.
+      if (GV.hasSection())
+        continue;
+    }
 
     Globals.push_back(&GV);
   }