hwasan: Move .note.hwasan.globals note to hwasan.module_ctor comdat.

[pcc]

Summary

As of D70146 lld GCs comdats as a group and no longer considers notes in
comdats to be GC roots, so we need to move the note to a comdat with a GC root
section (.init_array) in order to prevent lld from discarding the note.

[merge_guards_bot]

Unit tests: fail. 61974 tests passed, 1 failed and 783 were skipped.

failed: LLVM.Bindings/Go/go.test

clang-tidy: unknown.

clang-format: pass.

Build artifacts: diff.json, clang-format.patch, CMakeCache.txt, console-log.txt, test-results.xml

[eugenis]

LGTM

llvm/lib/Transforms/Instrumentation/HWAddressSanitizer.cpp

void HWAddressSanitizer::instrumentGlobals() {
   // 3) during construction, B accesses one of its "own" globals (actually
   //    interposed by A) and triggers a HWASAN failure due to the initialization
   //    for A not having happened yet
   //
   // Even without interposition it is possible to run into similar situations in
   // cases where two libraries mutually depend on each other.
   //
   // We only need one note per binary, so put everything for the note in a
-  // comdat.
-  Comdat *NoteComdat = M.getOrInsertComdat(kHwasanNoteName);
+  // comdat. This need to be a comdat with an .init_array section to prevent
+  // newer versions of lld from discarding the note.
+  Comdat *NoteComdat = M.getOrInsertComdat(kHwasanModuleCtorName);
 
   Type *Int8Arr0Ty = ArrayType::get(Int8Ty, 0);
   auto Start =
       new GlobalVariable(M, Int8Arr0Ty, true, GlobalVariable::ExternalLinkage,
                          nullptr, "__start_hwasan_globals");
   Start->setVisibility(GlobalValue::HiddenVisibility);
   Start->setDSOLocal(true);
   auto Stop =

llvm/test/Instrumentation/HWAddressSanitizer/globals.ll

 ; RUN: opt < %s -S -hwasan -mtriple=aarch64--linux-android29 | FileCheck --check-prefix=CHECK29 %s
 ; RUN: opt < %s -S -hwasan -mtriple=aarch64--linux-android30 | FileCheck --check-prefix=CHECK30 %s
 
 ; CHECK29-NOT: @hwasan.note
 ; CHECK29: @four = global
 
 ; CHECK30: @__start_hwasan_globals = external hidden constant [0 x i8]
 ; CHECK30: @__stop_hwasan_globals = external hidden constant [0 x i8]
 
-; CHECK30: @hwasan.note = private constant { i32, i32, i32, [8 x i8], i32, i32 } { i32 8, i32 8, i32 3, [8 x i8] c"LLVM\00\00\00\00", i32 trunc (i64 sub (i64 ptrtoint ([0 x i8]* @__start_hwasan_globals to i64), i64 ptrtoint ({ i32, i32, i32, [8 x i8], i32, i32 }* @hwasan.note to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([0 x i8]* @__stop_hwasan_globals to i64), i64 ptrtoint ({ i32, i32, i32, [8 x i8], i32, i32 }* @hwasan.note to i64)) to i32) }, section ".note.hwasan.globals", comdat, align 4
+; CHECK30: @hwasan.note = private constant { i32, i32, i32, [8 x i8], i32, i32 } { i32 8, i32 8, i32 3, [8 x i8] c"LLVM\00\00\00\00", i32 trunc (i64 sub (i64 ptrtoint ([0 x i8]* @__start_hwasan_globals to i64), i64 ptrtoint ({ i32, i32, i32, [8 x i8], i32, i32 }* @hwasan.note to i64)) to i32), i32 trunc (i64 sub (i64 ptrtoint ([0 x i8]* @__stop_hwasan_globals to i64), i64 ptrtoint ({ i32, i32, i32, [8 x i8], i32, i32 }* @hwasan.note to i64)) to i32) }, section ".note.hwasan.globals", comdat($hwasan.module_ctor), align 4
 
-; CHECK30: @hwasan.dummy.global = private constant [0 x i8] zeroinitializer, section "hwasan_globals", comdat($hwasan.note), !associated [[NOTE:![0-9]+]]
+; CHECK30: @hwasan.dummy.global = private constant [0 x i8] zeroinitializer, section "hwasan_globals", comdat($hwasan.module_ctor), !associated [[NOTE:![0-9]+]]
 
 ; CHECK30: @four.hwasan = private global { i32, [12 x i8] } { i32 1, [12 x i8] c"\00\00\00\00\00\00\00\00\00\00\00\AC" }, align 16
 ; CHECK30: @four.hwasan.descriptor = private constant { i32, i32 } { i32 trunc (i64 sub (i64 ptrtoint ({ i32, [12 x i8] }* @four.hwasan to i64), i64 ptrtoint ({ i32, i32 }* @four.hwasan.descriptor to i64)) to i32), i32 -1409286140 }, section "hwasan_globals", !associated [[FOUR:![0-9]+]]
 
 ; CHECK30: @sixteen.hwasan = private global [16 x i8] zeroinitializer, align 16
 ; CHECK30: @sixteen.hwasan.descriptor = private constant { i32, i32 } { i32 trunc (i64 sub (i64 ptrtoint ([16 x i8]* @sixteen.hwasan to i64), i64 ptrtoint ({ i32, i32 }* @sixteen.hwasan.descriptor to i64)) to i32), i32 -1392508912 }, section "hwasan_globals", !associated [[SIXTEEN:![0-9]+]]
 
 ; CHECK30: @huge.hwasan = private global [16777232 x i8] zeroinitializer, align 16