Objective C: use C++ exceptions on MinGW+GNUstep #77255

qmfrederik · 2024-01-07T20:58:10Z

The GNUstep Objective C runtime (libobjc2) is adding support for the GNU ABI on Windows (more specifically, MinGW). The libobjc2 runtime uses C++ exceptions in that configuration; this PR updates clang to act accordingly.

The corresponding change to libobjc2 is here: gnustep/libobjc2#267

github-actions · 2024-01-07T20:58:27Z

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llvmbot · 2024-01-07T20:58:52Z

@llvm/pr-subscribers-clang

@llvm/pr-subscribers-clang-codegen

Author: Frederik Carlier (qmfrederik)

Changes

The GNUstep Objective C runtime (libobjc2) is adding support for MinGW. This runtime uses C++ exceptions in that configuration.

Full diff: https://github.com/llvm/llvm-project/pull/77255.diff

3 Files Affected:

(modified) clang/lib/CodeGen/CGException.cpp (+11-7)
(modified) clang/lib/CodeGen/CGObjCGNU.cpp (+16-4)
(added) clang/test/CodeGenObjC/exceptions-personality.m (+53)

diff --git a/clang/lib/CodeGen/CGException.cpp b/clang/lib/CodeGen/CGException.cpp
index 0d507da5c1ba92..939f7962dcc635 100644
--- a/clang/lib/CodeGen/CGException.cpp
+++ b/clang/lib/CodeGen/CGException.cpp
@@ -145,8 +145,6 @@ static const EHPersonality &getCPersonality(const TargetInfo &Target,
 static const EHPersonality &getObjCPersonality(const TargetInfo &Target,
                                                const LangOptions &L) {
   const llvm::Triple &T = Target.getTriple();
-  if (T.isWindowsMSVCEnvironment())
-    return EHPersonality::MSVC_CxxFrameHandler3;
 
   switch (L.ObjCRuntime.getKind()) {
   case ObjCRuntime::FragileMacOSX:
@@ -156,7 +154,11 @@ static const EHPersonality &getObjCPersonality(const TargetInfo &Target,
   case ObjCRuntime::WatchOS:
     return EHPersonality::NeXT_ObjC;
   case ObjCRuntime::GNUstep:
-    if (L.ObjCRuntime.getVersion() >= VersionTuple(1, 7))
+    if (T.isOSCygMing())
+      return EHPersonality::GNU_CPlusPlus_SEH;
+    else if (T.isWindowsMSVCEnvironment())
+      return EHPersonality::MSVC_CxxFrameHandler3;
+    else if (L.ObjCRuntime.getVersion() >= VersionTuple(1, 7))
       return EHPersonality::GNUstep_ObjC;
     [[fallthrough]];
   case ObjCRuntime::GCC:
@@ -192,9 +194,6 @@ static const EHPersonality &getCXXPersonality(const TargetInfo &Target,
 /// and Objective-C exceptions are being caught.
 static const EHPersonality &getObjCXXPersonality(const TargetInfo &Target,
                                                  const LangOptions &L) {
-  if (Target.getTriple().isWindowsMSVCEnvironment())
-    return EHPersonality::MSVC_CxxFrameHandler3;
-
   switch (L.ObjCRuntime.getKind()) {
   // In the fragile ABI, just use C++ exception handling and hope
   // they're not doing crazy exception mixing.
@@ -210,7 +209,12 @@ static const EHPersonality &getObjCXXPersonality(const TargetInfo &Target,
     return getObjCPersonality(Target, L);
 
   case ObjCRuntime::GNUstep:
-    return EHPersonality::GNU_ObjCXX;
+    if (Target.getTriple().isWindowsMSVCEnvironment())
+      return EHPersonality::MSVC_CxxFrameHandler3;
+    else if (Target.getTriple().isOSCygMing())
+      return EHPersonality::GNU_CPlusPlus_SEH;
+    else
+      return EHPersonality::GNU_ObjCXX;
 
   // The GCC runtime's personality function inherently doesn't support
   // mixed EH.  Use the ObjC personality just to avoid returning null.
diff --git a/clang/lib/CodeGen/CGObjCGNU.cpp b/clang/lib/CodeGen/CGObjCGNU.cpp
index 4ca1a8cce64d89..5ace469c927045 100644
--- a/clang/lib/CodeGen/CGObjCGNU.cpp
+++ b/clang/lib/CodeGen/CGObjCGNU.cpp
@@ -819,7 +819,15 @@ class CGObjCGNUstep : public CGObjCGNU {
       SlotLookupSuperFn.init(&CGM, "objc_slot_lookup_super", SlotTy,
                              PtrToObjCSuperTy, SelectorTy);
       // If we're in ObjC++ mode, then we want to make
-      if (usesSEHExceptions) {
+      if (CGM.getTarget().getTriple().isOSCygMing() && isRuntime(ObjCRuntime::GNUstep, 2)) {
+        llvm::Type *VoidTy = llvm::Type::getVoidTy(VMContext);
+        // void *__cxa_begin_catch(void *e)
+        EnterCatchFn.init(&CGM, "__cxa_begin_catch", PtrTy, PtrTy);
+        // void __cxa_end_catch(void)
+        ExitCatchFn.init(&CGM, "__cxa_end_catch", VoidTy);
+        // void objc_exception_rethrow(void*)
+        ExceptionReThrowFn.init(&CGM, "__cxa_rethrow", PtrTy);
+      } else if (usesSEHExceptions) {
           llvm::Type *VoidTy = llvm::Type::getVoidTy(VMContext);
           // void objc_exception_rethrow(void)
           ExceptionReThrowFn.init(&CGM, "objc_exception_rethrow", VoidTy);
@@ -2210,7 +2218,11 @@ CGObjCGNU::CGObjCGNU(CodeGenModule &cgm, unsigned runtimeABIVersion,
 
   // void objc_exception_throw(id);
   ExceptionThrowFn.init(&CGM, "objc_exception_throw", VoidTy, IdTy);
-  ExceptionReThrowFn.init(&CGM, "objc_exception_throw", VoidTy, IdTy);
+  if ((CGM.getTarget().getTriple().isOSCygMing() && isRuntime(ObjCRuntime::GNUstep, 2))) {
+    ExceptionReThrowFn.init(&CGM, "objc_exception_rethrow", VoidTy, IdTy);
+  } else {
+    ExceptionReThrowFn.init(&CGM, "objc_exception_throw", VoidTy, IdTy);
+  }
   // int objc_sync_enter(id);
   SyncEnterFn.init(&CGM, "objc_sync_enter", IntTy, IdTy);
   // int objc_sync_exit(id);
@@ -2387,7 +2399,7 @@ llvm::Constant *CGObjCGNUstep::GetEHType(QualType T) {
   if (usesSEHExceptions)
     return CGM.getCXXABI().getAddrOfRTTIDescriptor(T);
 
-  if (!CGM.getLangOpts().CPlusPlus)
+  if (!CGM.getLangOpts().CPlusPlus && !(CGM.getTarget().getTriple().isOSCygMing() && isRuntime(ObjCRuntime::GNUstep, 2)))
     return CGObjCGNU::GetEHType(T);
 
   // For Objective-C++, we want to provide the ability to catch both C++ and
@@ -3993,7 +4005,7 @@ void CGObjCGNU::EmitThrowStmt(CodeGenFunction &CGF,
     ExceptionAsObject = CGF.ObjCEHValueStack.back();
     isRethrow = true;
   }
-  if (isRethrow && usesSEHExceptions) {
+  if (isRethrow && (usesSEHExceptions || (CGM.getTarget().getTriple().isOSCygMing() && isRuntime(ObjCRuntime::GNUstep, 2)))) {
     // For SEH, ExceptionAsObject may be undef, because the catch handler is
     // not passed it for catchalls and so it is not visible to the catch
     // funclet.  The real thrown object will still be live on the stack at this
diff --git a/clang/test/CodeGenObjC/exceptions-personality.m b/clang/test/CodeGenObjC/exceptions-personality.m
new file mode 100644
index 00000000000000..c29f7483715d88
--- /dev/null
+++ b/clang/test/CodeGenObjC/exceptions-personality.m
@@ -0,0 +1,53 @@
+// RUN: %clang_cc1 -triple x86_64-w64-windows-gnu  -emit-llvm -fobjc-runtime=gnustep-2.0 -fexceptions -fobjc-exceptions -o %t %s
+// RUN: FileCheck --check-prefixes=CHECK-MINGW-OBJC2 < %t %s
+
+// RUN: %clang_cc1 -triple x86_64-w64-windows-gnu  -emit-llvm -fobjc-runtime=gcc -fexceptions -fobjc-exceptions -o %t %s
+// RUN: FileCheck --check-prefixes=CHECK-MINGW-GCC < %t %s
+
+// RUN: %clang_cc1 -triple x86_64-w64-windows-msvc  -emit-llvm -fobjc-runtime=gnustep-2.0 -fexceptions -fobjc-exceptions -o %t %s
+// RUN: FileCheck --check-prefixes=CHECK-MSVC-OBJC2 < %t %s
+
+// RUN: %clang_cc1 -triple x86_64-pc-linux-gnu  -emit-llvm -fobjc-runtime=gnustep-2.0 -fexceptions -fobjc-exceptions -o %t %s
+// RUN: FileCheck --check-prefixes=CHECK-LINUX-OBJC2 < %t %s
+
+// RUN: %clang_cc1 -triple x86_64-pc-linux-gnu  -emit-llvm -fobjc-runtime=gcc -fexceptions -fobjc-exceptions -o %t %s
+// RUN: FileCheck --check-prefixes=CHECK-LINUX-GCC < %t %s
+@interface Foo @end
+
+void throwing(void) {
+  @try
+  {
+    // CHECK-MINGW-OBJC2: personality ptr @__gxx_personality_seh0
+    // CHECK-MINGW-OBJC2: invoke void @objc_exception_throw
+
+    // CHECK-MINGW-GCC: personality ptr @__gnu_objc_personality_v0
+    // CHECK-MINGW-GCC: invoke void @objc_exception_throw
+
+    // CHECK-MSVC-OBJC2: personality ptr @__CxxFrameHandler3
+    // CHECK-MSVC-OBJC2: invoke void @objc_exception_throw
+
+    // CHECK-LINUX-OBJC2: personality ptr @__gnustep_objc_personality_v0
+    // CHECK-LINUX-OBJC2: invoke void @objc_exception_throw
+
+    // CHECK-LINUX-GCC: personality ptr @__gnu_objc_personality_v0
+    @throw(@"error!");
+  }
+  @catch(...) 
+  {
+    // CHECK-MINGW-OBJC2: call ptr @__cxa_begin_catch
+    // CHECK-MINGW-OBJC2: invoke ptr @__cxa_rethrow
+    // CHECK-MINGW-OBJC2: invoke void @__cxa_end_catch
+    
+    // CHECK-MINGW-GCC: call void @objc_exception_throw
+
+    // CHECK-MSVC-OBJC2: call void @objc_exception_rethrow
+
+    // CHECK-LINUX-OBJC2: call ptr @objc_begin_catch
+    // CHECK-LINUX-OBJC2: invoke void @objc_exception_throw
+    // CHECK-LINUX-OBJC2: invoke void @objc_end_catch()
+
+    // CHECK-LINUX-GCC: invoke void @objc_exception_throw
+    
+    @throw;
+  }
+}
\ No newline at end of file

github-actions · 2024-01-07T21:00:30Z

✅ With the latest revision this PR passed the C/C++ code formatter.

clang/lib/CodeGen/CGException.cpp

qmfrederik · 2024-01-07T21:20:44Z

/cc @davidchisnall

clang/lib/CodeGen/CGObjCGNU.cpp

davidchisnall · 2024-01-08T08:29:25Z

The failing format CI isn’t in this PR, rebasing to (hopefully) fix it

compnerd · 2024-01-09T01:09:39Z

clang/lib/CodeGen/CGException.cpp

+    if (Target.getTriple().isOSCygMing())
+      return EHPersonality::GNU_CPlusPlus_SEH;
+    else
+      return EHPersonality::GNU_ObjCXX;


This might be nicer as a ternary return.

compnerd · 2024-01-09T01:11:01Z

clang/lib/CodeGen/CGObjCGNU.cpp

+        // void objc_exception_rethrow(void*)
+        ExceptionReThrowFn.init(&CGM, "__cxa_rethrow", PtrTy);
+      } else if (usesSEHExceptions) {
+        llvm::Type *VoidTy = llvm::Type::getVoidTy(VMContext);


Why not hoist this? It is used across multiple branches.

Good remark, thanks. Fixed this.

compnerd · 2024-01-09T01:12:17Z

clang/lib/CodeGen/CGObjCGNU.cpp

-  if (isRethrow && usesSEHExceptions) {
+  if (isRethrow &&
+      (usesSEHExceptions || (CGM.getTarget().getTriple().isOSCygMing() &&
+                             isRuntime(ObjCRuntime::GNUstep, 2)))) {


Does it make sense to introduce a usesCxxExceptions variable?

Yes, that makes the intent clearer. I changed this.

qmfrederik · 2024-01-09T09:49:28Z

@compnerd Thanks for you feedback, I addressed your comments.

qmfrederik · 2024-01-09T13:41:00Z

@compnerd @davidchisnall I've addressed the feedback and CI is (mostly) green. The build failure on Windows seems unrelated:

# Removing c:/ws\src
# Creating "c:/ws\src"
> git clone -v -- https://github.com/llvm-premerge-tests/llvm-project.git .
Cloning into '.'...
remote: Internal Server Error
fatal: unable to access 'https://github.com/llvm-premerge-tests/llvm-project.git/': The requested URL returned error: 500

davidchisnall · 2024-01-09T14:41:49Z

I'd like CI to be green. Hopefully the failure is transient, but I don't seem to be able to kick off a rerun. Maybe once others start passing, you can squash the two commits and force push to restart it?

qmfrederik · 2024-01-09T15:27:52Z

Looks like there was an intermittent issue with GitHub, which should be resolved now. I've squashed and pushed. Fingers crossed!

qmfrederik · 2024-01-09T18:45:05Z

CI looks green, let me know if there's anything else you need from me on this PR!

compnerd · 2024-01-10T02:06:16Z

clang/lib/CodeGen/CGObjCGNU.cpp

@@ -2210,7 +2219,11 @@ CGObjCGNU::CGObjCGNU(CodeGenModule &cgm, unsigned runtimeABIVersion,

  // void objc_exception_throw(id);
  ExceptionThrowFn.init(&CGM, "objc_exception_throw", VoidTy, IdTy);
-  ExceptionReThrowFn.init(&CGM, "objc_exception_throw", VoidTy, IdTy);
+  if (usesCxxExceptions) {
+    ExceptionReThrowFn.init(&CGM, "objc_exception_rethrow", VoidTy, IdTy);


I would say that a ternary to select between the exception model and identify the name would be better as you are just selecting the label.

davidchisnall · 2024-01-10T13:52:57Z

It looks as if three tests are failing in CI:

Clang :: CodeGenObjC/2007-04-03-ObjcEH.m
Clang :: CodeGenObjC/exceptions-personality.m
Clang :: Coverage/codegen-gnu.m

The GNUstep Objective C runtime (libobjc2) is adding support for MinGW. This runtime uses C++ exceptions in that configuration.

qmfrederik · 2024-01-10T16:32:10Z

@davidchisnall Apologies, that was a fat-finger mistake while addressing the latest feedback. CI is green now.

The GNUstep Objective C runtime (libobjc2) is adding support for the GNU ABI on Windows (more specifically, MinGW). The libobjc2 runtime uses C++ exceptions in that configuration; this PR updates clang to act accordingly. The corresponding change to libobjc2 is here: gnustep/libobjc2#267

llvmbot added clang Clang issues not falling into any other category clang:codegen labels Jan 7, 2024

qmfrederik mentioned this pull request Jan 7, 2024

Use C++ exceptions unconditionally for Objective-C[++] on MinGW gnustep/libobjc2#267

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Add test variant testing GCC runtime compatibility gnustep/libobjc2#259

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Objective C: use C++ exceptions on MinGW+GNUstep

9ede4ec

The GNUstep Objective C runtime (libobjc2) is adding support for MinGW. This runtime uses C++ exceptions in that configuration.

qmfrederik force-pushed the mingw-exceptions branch from 4d41874 to 9ede4ec Compare January 10, 2024 14:01

davidchisnall merged commit 1d5106d into llvm:main Jan 10, 2024
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qmfrederik deleted the mingw-exceptions branch January 10, 2024 16:54

This was referenced Jan 15, 2024

Clang: Backport fixes for Objective-C on mingw msys2/MINGW-packages#19767

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MinGW: Add dllimport/dllexport attributes when compiling with clang gnustep/libs-base#363

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qmfrederik mentioned this pull request Feb 4, 2024

libobjc2: New package msys2/MINGW-packages#19948

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Objective C: use C++ exceptions on MinGW+GNUstep #77255

Objective C: use C++ exceptions on MinGW+GNUstep #77255

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