[PATCH] D72936: hwasan: Move .note.hwasan.globals note to hwasan.module_ctor comdat.

[Peter Collingbourne via Phabricator via llvm-commits]

pcc created this revision.
pcc added a reviewer: eugenis.
Herald added a subscriber: hiraditya.
Herald added a project: LLVM.

As of D70146 <https://reviews.llvm.org/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.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D72936

Files:
  llvm/lib/Transforms/Instrumentation/HWAddressSanitizer.cpp
  llvm/test/Instrumentation/HWAddressSanitizer/globals.ll


Index: llvm/test/Instrumentation/HWAddressSanitizer/globals.ll
===================================================================
--- llvm/test/Instrumentation/HWAddressSanitizer/globals.ll
+++ llvm/test/Instrumentation/HWAddressSanitizer/globals.ll
@@ -7,9 +7,9 @@
 ; 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]+]]
Index: llvm/lib/Transforms/Instrumentation/HWAddressSanitizer.cpp
===================================================================
--- llvm/lib/Transforms/Instrumentation/HWAddressSanitizer.cpp
+++ llvm/lib/Transforms/Instrumentation/HWAddressSanitizer.cpp
@@ -1325,8 +1325,9 @@
   // 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 =


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