[PATCH] D157962: [GNU ObjC] Unconditionally emit section markers.

[David Chisnall via Phabricator via cfe-commits]

theraven created this revision.
Herald added a project: All.
theraven requested review of this revision.
Herald added a project: clang.
Herald added a subscriber: cfe-commits.

In the GNUstep v2 ABI (on ELF), we rely on the linker-inserted section
start and stop markers.  These only exist when binary has something in
the relevant sections.  To ensure that they exist, compilation units
that omit one of the components emit an empty object into the section
that it's not putting anything in.  These empty objects are COMDATs and
are merged in the final version.

Unfortunately, there is a corner case where the entry exists in the code
emitted by the front end but is then elided during optimisation.  We
already unconditionally emitted an empty selector to avoid this case for
message sends but it was still a problem for constant strings.

This change unconditionally emits these placeholders for everything.
This results in very slightly larger .o files but ensures that any
future optimisation that elides more things will not prevent compilation
and so reduces fragility.

Fixes #47536


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D157962

Files:
  clang/lib/CodeGen/CGObjCGNU.cpp


Index: clang/lib/CodeGen/CGObjCGNU.cpp
===================================================================
--- clang/lib/CodeGen/CGObjCGNU.cpp
+++ clang/lib/CodeGen/CGObjCGNU.cpp
@@ -1614,32 +1614,24 @@
     if (!CGM.getTriple().isOSBinFormatCOFF()) {
       createNullGlobal(".objc_null_selector", {NULLPtr, NULLPtr},
           sectionName<SelectorSection>());
-      if (Categories.empty())
-        createNullGlobal(".objc_null_category", {NULLPtr, NULLPtr,
-                      NULLPtr, NULLPtr, NULLPtr, NULLPtr, NULLPtr},
-            sectionName<CategorySection>());
-      if (!EmittedClass) {
-        createNullGlobal(".objc_null_cls_init_ref", NULLPtr,
-            sectionName<ClassSection>());
-        createNullGlobal(".objc_null_class_ref", { NULLPtr, NULLPtr },
-            sectionName<ClassReferenceSection>());
-      }
-      if (!EmittedProtocol)
-        createNullGlobal(".objc_null_protocol", {NULLPtr, NULLPtr, NULLPtr,
-            NULLPtr, NULLPtr, NULLPtr, NULLPtr, NULLPtr, NULLPtr, NULLPtr,
-            NULLPtr}, sectionName<ProtocolSection>());
-      if (!EmittedProtocolRef)
-        createNullGlobal(".objc_null_protocol_ref", {NULLPtr},
-            sectionName<ProtocolReferenceSection>());
-      if (ClassAliases.empty())
-        createNullGlobal(".objc_null_class_alias", { NULLPtr, NULLPtr },
-            sectionName<ClassAliasSection>());
-      if (ConstantStrings.empty()) {
-        auto i32Zero = llvm::ConstantInt::get(Int32Ty, 0);
-        createNullGlobal(".objc_null_constant_string", { NULLPtr, i32Zero,
-            i32Zero, i32Zero, i32Zero, NULLPtr },
-            sectionName<ConstantStringSection>());
-      }
+      createNullGlobal(".objc_null_category", {NULLPtr, NULLPtr,
+                    NULLPtr, NULLPtr, NULLPtr, NULLPtr, NULLPtr},
+          sectionName<CategorySection>());
+      createNullGlobal(".objc_null_cls_init_ref", NULLPtr,
+          sectionName<ClassSection>());
+      createNullGlobal(".objc_null_class_ref", { NULLPtr, NULLPtr },
+          sectionName<ClassReferenceSection>());
+      createNullGlobal(".objc_null_protocol", {NULLPtr, NULLPtr, NULLPtr,
+          NULLPtr, NULLPtr, NULLPtr, NULLPtr, NULLPtr, NULLPtr, NULLPtr,
+          NULLPtr}, sectionName<ProtocolSection>());
+      createNullGlobal(".objc_null_protocol_ref", {NULLPtr},
+          sectionName<ProtocolReferenceSection>());
+      createNullGlobal(".objc_null_class_alias", { NULLPtr, NULLPtr },
+          sectionName<ClassAliasSection>());
+      auto i32Zero = llvm::ConstantInt::get(Int32Ty, 0);
+      createNullGlobal(".objc_null_constant_string", { NULLPtr, i32Zero,
+          i32Zero, i32Zero, i32Zero, NULLPtr },
+          sectionName<ConstantStringSection>());
     }
     ConstantStrings.clear();
     Categories.clear();


-------------- next part --------------
A non-text attachment was scrubbed...
Name: D157962.550247.patch
Type: text/x-patch
Size: 2800 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/cfe-commits/attachments/20230815/a034cd36/attachment.bin>