[sanitizer] Place module_ctor/module_dtor in llvm.used

This removes an abuse of ELF linker behaviors while keeping Mach-O/COFF linker
behaviors unchanged.

ELF: when module_ctor is in a comdat, this patch removes reliance on a linker
abuse (an SHT_INIT_ARRAY in a section group retains the whole group) by using
SHF_GNU_RETAIN. No linker behavior difference when module_ctor is not in a comdat.

Mach-O: module_ctor gets `N_NO_DEAD_STRIP`. No linker behavior difference
because module_ctor is already referenced by a `S_MOD_INIT_FUNC_POINTERS`
section (GC root).

PE/COFF: no-op. SanitizerCoverage already appends module_ctor to `llvm.used`.
Other sanitizers: llvm.used for local linkage is not implemented in
`TargetLoweringObjectFileCOFF::emitLinkerDirectives` (once implemented or
switched to a non-local linkage, COFF can use module_ctor in comdat (i.e.
generalize ELF-specific rL301586)).

There is no object file size difference.

Reviewed By: vitalybuka

Differential Revision: https://reviews.llvm.org/D106246

Author: MaskRay

llvm/lib/Transforms/Instrumentation/AddressSanitizer.cpp

@@ -2138,6 +2138,8 @@ Instruction *ModuleAddressSanitizer::CreateAsanModuleDtor(Module &M) {
       GlobalValue::InternalLinkage, 0, kAsanModuleDtorName, &M);
   AsanDtorFunction->addAttribute(AttributeList::FunctionIndex,
                                  Attribute::NoUnwind);
+  // Ensure Dtor cannot be discarded, even if in a comdat.
+  appendToUsed(M, {AsanDtorFunction});
   BasicBlock *AsanDtorBB = BasicBlock::Create(*C, "", AsanDtorFunction);
 
   return ReturnInst::Create(*C, AsanDtorBB);

llvm/lib/Transforms/Instrumentation/SanitizerCoverage.cpp

@@ -384,7 +384,6 @@ Function *ModuleSanitizerCoverage::CreateInitCallsForSections(
     // to include the sancov constructor. This way the linker can deduplicate
     // the constructors but always leave one copy.
     CtorFunc->setLinkage(GlobalValue::WeakODRLinkage);
-    appendToUsed(M, CtorFunc);
   }
   return CtorFunc;
 }

llvm/lib/Transforms/Utils/ModuleUtils.cpp

@@ -128,6 +128,8 @@ Function *llvm::createSanitizerCtor(Module &M, StringRef CtorName) {
   Ctor->addAttribute(AttributeList::FunctionIndex, Attribute::NoUnwind);
   BasicBlock *CtorBB = BasicBlock::Create(M.getContext(), "", Ctor);
   ReturnInst::Create(M.getContext(), CtorBB);
+  // Ensure Ctor cannot be discarded, even if in a comdat.
+  appendToUsed(M, {Ctor});
   return Ctor;
 }
 

llvm/test/Instrumentation/AddressSanitizer/basic.ll

@@ -8,7 +8,8 @@
 
 target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64"
 target triple = "x86_64-unknown-linux-gnu"
-; CHECK: @llvm.global_ctors = {{.*}}@asan.module_ctor
+; CHECK: @llvm.used = appending global [1 x i8*] [i8* bitcast (void ()* @asan.module_ctor to i8*)]
+; CHECK: @llvm.global_ctors = {{.*}}{ i32 1, void ()* @asan.module_ctor, i8* bitcast (void ()* @asan.module_ctor to i8*) }
 
 define i32 @test_load(i32* %a) sanitize_address {
 ; CHECK-LABEL: @test_load

llvm/test/Instrumentation/AddressSanitizer/instrument_global.ll

@@ -10,8 +10,9 @@ target triple = "x86_64-unknown-linux-gnu"
 ; module ctor/dtor
 
 ; CHECK: @___asan_gen_ = private constant [8 x i8] c"<stdin>\00", align 1
-; CHECK: llvm.global_ctors
-; CHECK: llvm.global_dtors
+; CHECK: @llvm.used = appending global [2 x i8*] [i8* bitcast (void ()* @asan.module_ctor to i8*), i8* bitcast (void ()* @asan.module_dtor to i8*)], section "llvm.metadata"
+; CHECK: @llvm.global_ctors = appending global [1 x { i32, void ()*, i8* }] [{ i32, void ()*, i8* } { i32 1, void ()* @asan.module_ctor, i8* bitcast (void ()* @asan.module_ctor to i8*) }]
+; CHECK: @llvm.global_dtors = appending global [1 x { i32, void ()*, i8* }] [{ i32, void ()*, i8* } { i32 1, void ()* @asan.module_dtor, i8* bitcast (void ()* @asan.module_dtor to i8*) }]
 
 ; Test that we don't instrument global arrays with static initializer
 ; indexed with constants in-bounds. But instrument all other cases.

llvm/test/Instrumentation/HWAddressSanitizer/basic.ll

@@ -11,6 +11,7 @@
 ; RUN: opt < %s -passes=hwasan -hwasan-recover=0 -hwasan-mapping-offset=0 -S | FileCheck %s --check-prefixes=CHECK,ABORT
 ; RUN: opt < %s -passes=hwasan -hwasan-recover=1 -hwasan-mapping-offset=0 -S | FileCheck %s --check-prefixes=CHECK,RECOVER,RECOVER-ZERO-BASED-SHADOW
 
+; CHECK: @llvm.used = appending global [1 x i8*] [i8* bitcast (void ()* @hwasan.module_ctor to i8*)]
 ; CHECK: @llvm.global_ctors = appending global [1 x { i32, void ()*, i8* }] [{ i32, void ()*, i8* } { i32 0, void ()* @hwasan.module_ctor, i8* bitcast (void ()* @hwasan.module_ctor to i8*) }]
 
 target datalayout = "e-m:e-i8:8:32-i16:16:32-i64:64-i128:128-n32:64-S128"

llvm/test/Instrumentation/HeapProfiler/basic.ll

@@ -9,7 +9,9 @@
 
 target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64"
 target triple = "x86_64-unknown-linux-gnu"
-; CHECK: @llvm.global_ctors = {{.*}}@memprof.module_ctor
+
+; CHECK: @llvm.used = appending global [1 x i8*] [i8* bitcast (void ()* @memprof.module_ctor to i8*)]
+; CHECK: @llvm.global_ctors = appending global [1 x { i32, void ()*, i8* }] [{ i32, void ()*, i8* } { i32 1, void ()* @memprof.module_ctor, i8* null }]
 
 define i32 @test_load(i32* %a) {
 entry:

llvm/test/Instrumentation/MemorySanitizer/msan_basic.ll

@@ -10,6 +10,7 @@
 target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64-S128"
 target triple = "x86_64-unknown-linux-gnu"
 
+; CHECK: @llvm.used = appending global [1 x i8*] [i8* bitcast (void ()* @msan.module_ctor to i8*)]
 ; CHECK: @llvm.global_ctors {{.*}} { i32 0, void ()* @msan.module_ctor, i8* null }
 
 ; Check the presence and the linkage type of __msan_track_origins and

llvm/test/Instrumentation/SanitizerCoverage/inline-bool-flag.ll

@@ -6,7 +6,7 @@
 ; CHECK:      @__sancov_gen_ = private global [1 x i1] zeroinitializer, section "__sancov_bools", comdat($foo), align 1{{$}}
 ; CHECK:      @__start___sancov_bools = extern_weak hidden global i1
 ; CHECK-NEXT: @__stop___sancov_bools = extern_weak hidden global i1
-; CHECK-NOT:  @llvm.used =
+; CHECK:      @llvm.used = appending global [1 x i8*] [i8* bitcast (void ()* @sancov.module_ctor_bool_flag to i8*)], section "llvm.metadata"
 ; CHECK:      @llvm.compiler.used = appending global [1 x i8*] [i8* bitcast ([1 x i1]* @__sancov_gen_ to i8*)], section "llvm.metadata"
 
 target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64"

llvm/test/Instrumentation/SanitizerCoverage/trace-pc-guard.ll

@@ -18,9 +18,9 @@
 ; WIN:        @__sancov_gen_ = private global [3 x i32] zeroinitializer, section ".SCOV$GM", comdat($foo), align 4{{$}}
 ; WIN-NEXT:   @__sancov_gen_.1 = private global [1 x i32] zeroinitializer, section ".SCOV$GM", comdat($CallViaVptr), align 4{{$}}
 
-; ELF-NOT:    @llvm.used =
+; ELF:        @llvm.used = appending global [1 x i8*] [i8* bitcast (void ()* @sancov.module_ctor_trace_pc_guard to i8*)]
 ; ELF:        @llvm.compiler.used = appending global [2 x i8*] [i8* bitcast ([3 x i32]* @__sancov_gen_ to i8*), i8* bitcast ([1 x i32]* @__sancov_gen_.1 to i8*)], section "llvm.metadata"
-; MACHO:      @llvm.used = appending global [2 x i8*] [i8* bitcast ([3 x i32]* @__sancov_gen_ to i8*), i8* bitcast ([1 x i32]* @__sancov_gen_.1 to i8*)], section "llvm.metadata"
+; MACHO:      @llvm.used = appending global [3 x i8*] [i8* bitcast (void ()* @sancov.module_ctor_trace_pc_guard to i8*), i8* bitcast ([3 x i32]* @__sancov_gen_ to i8*), i8* bitcast ([1 x i32]* @__sancov_gen_.1 to i8*)]
 ; MACHO-NOT:  @llvm.compiler.used =
 ; WIN:        @llvm.used = appending global [1 x i8*] [i8* bitcast (void ()* @sancov.module_ctor_trace_pc_guard to i8*)], section "llvm.metadata"
 ; WIN-NEXT:   @llvm.compiler.used = appending global [2 x i8*] [i8* bitcast ([3 x i32]* @__sancov_gen_ to i8*), i8* bitcast ([1 x i32]* @__sancov_gen_.1 to i8*)], section "llvm.metadata"

llvm/test/Instrumentation/ThreadSanitizer/tsan_basic.ll

@@ -10,6 +10,7 @@ entry:
   ret i32 %tmp1
 }
 
+; CHECK: @llvm.used = appending global [1 x i8*] [i8* bitcast (void ()* @tsan.module_ctor to i8*)]
 ; CHECK: @llvm.global_ctors = {{.*}}@tsan.module_ctor
 
 ; CHECK: define i32 @read_4_bytes(i32* %a)