Disable atexit()-based lowering when LTO'ing kernel/kext code

[yln]

Summary

The kernel and kext environment does not provide the __cxa_atexit() function, so we can't use it for lowering global module destructors.
Unfortunately, just querying for "compiling for kernel/kext?" in the LTO pipeline isn't possible (kernel/kext identifier isn't part of the triple yet) so we need to pass down a CodeGen flag.

rdar://93536111

[ab]

A comment inline, but LGTM otherwise, thanks!

llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp

1208

stray fatal_error?

clang/lib/Driver/ToolChains/Darwin.cpp

if (A->getOption().matches(options::OPT_fglobal_isel)) {
       CmdArgs.push_back("-mllvm");
       CmdArgs.push_back("-global-isel");
       // Disable abort and fall back to SDAG silently.
       CmdArgs.push_back("-mllvm");
       CmdArgs.push_back("-global-isel-abort=0");
     }
   }
 
+  if (Args.hasArg(options::OPT_mkernel) ||
+      Args.hasArg(options::OPT_fapple_kext) ||
+      Args.hasArg(options::OPT_ffreestanding)) {
+    CmdArgs.push_back("-mllvm");
+    CmdArgs.push_back("-disable-atexit-based-global-dtor-lowering");
+  }
+
   Args.AddLastArg(CmdArgs, options::OPT_prebind);
   Args.AddLastArg(CmdArgs, options::OPT_noprebind);
   Args.AddLastArg(CmdArgs, options::OPT_nofixprebinding);
   Args.AddLastArg(CmdArgs, options::OPT_prebind__all__twolevel__modules);
   Args.AddLastArg(CmdArgs, options::OPT_read__only__relocs);
   Args.AddAllArgs(CmdArgs, options::OPT_sectcreate);
   Args.AddAllArgs(CmdArgs, options::OPT_sectorder);
   Args.AddAllArgs(CmdArgs, options::OPT_seg1addr);

clang/test/Driver/darwin-ld-lto.c

 
 
 // Check that we pass through -fglobal-isel flags to libLTO.
 // RUN: %clang -target arm64-apple-darwin %s -flto -fglobal-isel -### 2>&1 | \
 // RUN:   FileCheck --check-prefix=GISEL %s
 // GISEL: {{ld(.exe)?"}}
 // GISEL: "-mllvm" "-global-isel"
 // GISEL: "-mllvm" "-global-isel-abort=0"
+
+
+// Check that we disable atexit()-based global destructor lowering when
+// compiling/linking for kernel/kext/freestanding.
+// RUN: %clang -target arm64-apple-darwin %s -flto -fapple-kext -### 2>&1 | \
+// RUN:   FileCheck --check-prefix=KEXT %s
+// KEXT: {{ld(.exe)?"}}
+// KEXT: "-mllvm" "-disable-atexit-based-global-dtor-lowering"

llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp

PersonalityEncoding =
       dwarf::DW_EH_PE_indirect | dwarf::DW_EH_PE_pcrel | dwarf::DW_EH_PE_sdata4;
   LSDAEncoding = dwarf::DW_EH_PE_pcrel;
   TTypeEncoding =
       dwarf::DW_EH_PE_indirect | dwarf::DW_EH_PE_pcrel | dwarf::DW_EH_PE_sdata4;
 }
 
 MCSection *TargetLoweringObjectFileMachO::getStaticDtorSection(
     unsigned Priority, const MCSymbol *KeySym) const {
-  report_fatal_error("@llvm.global_dtors should have been lowered already");
+  return StaticDtorSection;
+  // In userspace, we lower global destructors via atexit(), but kernel/kext
+  // environments do not provide this function so we still need to support the
+  // legacy way here.
+  // See the -disable-atexit-based-global-dtor-lowering CodeGen flag for more
+  // context.
 }
 
 void TargetLoweringObjectFileMachO::emitModuleMetadata(MCStreamer &Streamer,
                                                        Module &M) const {
   // Emit the linker options if present.
   if (auto *LinkerOptions = M.getNamedMetadata("llvm.linker.options")) {
     for (const auto *Option : LinkerOptions->operands()) {
       SmallVector<std::string, 4> StrOptions;

llvm/lib/CodeGen/TargetPassConfig.cpp

 static cl::opt<bool> DisableConstantHoisting("disable-constant-hoisting",
     cl::Hidden, cl::desc("Disable ConstantHoisting"));
 static cl::opt<bool> DisableCGP("disable-cgp", cl::Hidden,
     cl::desc("Disable Codegen Prepare"));
 static cl::opt<bool> DisableCopyProp("disable-copyprop", cl::Hidden,
     cl::desc("Disable Copy Propagation pass"));
 static cl::opt<bool> DisablePartialLibcallInlining("disable-partial-libcall-inlining",
     cl::Hidden, cl::desc("Disable Partial Libcall Inlining"));
+static cl::opt<bool> DisableAtExitBasedGlobalDtorLowering(
+    "disable-atexit-based-global-dtor-lowering", cl::Hidden,
+    cl::desc("For MachO, disable atexit()-based global destructor lowering"));
 static cl::opt<bool> EnableImplicitNullChecks(
     "enable-implicit-null-checks",
     cl::desc("Fold null checks into faulting memory operations"),
     cl::init(false), cl::Hidden);
 static cl::opt<bool> DisableMergeICmps("disable-mergeicmps",
     cl::desc("Disable MergeICmps Pass"),
     cl::init(false), cl::Hidden);
 static cl::opt<bool> PrintLSR("print-lsr-output", cl::Hidden,
void TargetPassConfig::addIRPasses() {
   // Run GC lowering passes for builtin collectors
   // TODO: add a pass insertion point here
   addPass(&GCLoweringID);
   addPass(&ShadowStackGCLoweringID);
   addPass(createLowerConstantIntrinsicsPass());
 
   // For MachO, lower @llvm.global_dtors into @llvm.global_ctors with
   // __cxa_atexit() calls to avoid emitting the deprecated __mod_term_func.
-  if (TM->getTargetTriple().isOSBinFormatMachO())
+  if (TM->getTargetTriple().isOSBinFormatMachO() &&
+      !DisableAtExitBasedGlobalDtorLowering)
     addPass(createLowerGlobalDtorsLegacyPass());
 
   // Make sure that no unreachable blocks are instruction selected.
   addPass(createUnreachableBlockEliminationPass());
 
   // Prepare expensive constants for SelectionDAG.
   if (getOptLevel() != CodeGenOpt::None && !DisableConstantHoisting)
     addPass(createConstantHoistingPass());

llvm/test/CodeGen/ARM/ctors_dtors.ll

 ; RUN: llc < %s -mtriple=arm-apple-darwin  | FileCheck %s -check-prefix=DARWIN
+; RUN: llc < %s -mtriple=arm-apple-darwin -disable-atexit-based-global-dtor-lowering  | FileCheck %s -check-prefix=DARWIN-LEGACY
 ; RUN: llc < %s -mtriple=arm-linux-gnu -target-abi=apcs  | FileCheck %s -check-prefix=ELF
 ; RUN: llc < %s -mtriple=arm-linux-gnueabi | FileCheck %s -check-prefix=GNUEABI
 
 ; DARWIN: l_register_call_dtors:
 ; DARWIN: bl  ___cxa_atexit
 ; DARWIN: .section  __DATA,__mod_init_func,mod_init_funcs
 ; DARWIN-NOT: __mod_term_func
 
+; DARWIN-LEGACY-NOT: atexit
+; DARWIN-LEGACY: .section __DATA,__mod_init_func,mod_init_funcs
+; DARWIN-LEGACY: .section __DATA,__mod_term_func,mod_term_funcs
+
 ; ELF: .section .ctors,"aw",%progbits
 ; ELF: .section .dtors,"aw",%progbits
 
 ; GNUEABI: .section .init_array,"aw",%init_array
 ; GNUEABI: .section .fini_array,"aw",%fini_array
 
 @llvm.global_ctors = appending global [1 x { i32, ptr, ptr }] [ { i32, ptr, ptr } { i32 65535, ptr @__mf_init, ptr null } ]                ; <ptr> [#uses=0]
 @llvm.global_dtors = appending global [1 x { i32, ptr, ptr }] [ { i32, ptr, ptr } { i32 65535, ptr @__mf_fini, ptr null } ]                ; <ptr> [#uses=0]