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

The kernel and kext environments do 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 Differential Revision: https://reviews.llvm.org/D148967
llvm · Apr 25, 2023 · c3f0153 · c3f0153
1 parent 09d879d
commit c3f0153
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Showing 5 changed files with 31 additions and 2 deletions.
diff --git a/clang/lib/Driver/ToolChains/Darwin.cpp b/clang/lib/Driver/ToolChains/Darwin.cpp
@@ -393,6 +393,13 @@ void darwin::Linker::AddLinkArgs(Compilation &C, const ArgList &Args,
     }
   }
 
+  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);

diff --git a/clang/test/Driver/darwin-ld-lto.c b/clang/test/Driver/darwin-ld-lto.c
@@ -40,3 +40,11 @@
 // 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"
diff --git a/llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp b/llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp
@@ -1202,7 +1202,12 @@ void TargetLoweringObjectFileMachO::Initialize(MCContext &Ctx,
 
 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,

diff --git a/llvm/lib/CodeGen/TargetPassConfig.cpp b/llvm/lib/CodeGen/TargetPassConfig.cpp
@@ -100,6 +100,9 @@ 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"),
@@ -878,7 +881,8 @@ void TargetPassConfig::addIRPasses() {
 
   // 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.

diff --git a/llvm/test/CodeGen/ARM/ctors_dtors.ll b/llvm/test/CodeGen/ARM/ctors_dtors.ll
@@ -1,4 +1,5 @@
 ; 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
 
@@ -7,6 +8,10 @@
 ; 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