[PATCH] D66492: [Clang][CodeGen] set alias linkage on QualType

[Nick Desaulniers via Phabricator via cfe-commits]

nickdesaulniers created this revision.
nickdesaulniers added a reviewer: rsmith.
Herald added subscribers: cfe-commits, kristof.beyls, javed.absar.
Herald added a project: clang.

It seems that CodeGen was always using ExternalLinkage when emitting a
GlobalDecl with __attribute__((alias)). This leads to symbol
redefinitions (ODR) that cause failures at link time for static aliases.
This is readily attempting to link an ARM (32b) allyesconfig Linux
kernel built with Clang.

Reported-by: nathanchance
Suggested-by: ihalip
Link: https://github.com/ClangBuiltLinux/linux/issues/631


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D66492

Files:
  clang/lib/CodeGen/CodeGenModule.cpp
  clang/test/CodeGen/alias.c


Index: clang/test/CodeGen/alias.c
===================================================================
--- clang/test/CodeGen/alias.c
+++ clang/test/CodeGen/alias.c
@@ -2,6 +2,7 @@
 // RUN: %clang_cc1 -triple i386-pc-linux-gnu -emit-llvm -o - %s | FileCheck -check-prefix=CHECKBASIC %s
 // RUN: %clang_cc1 -triple armv7a-eabi -mfloat-abi hard -emit-llvm -o - %s | FileCheck -check-prefix=CHECKCC %s
 // RUN: %clang_cc1 -triple armv7a-eabi -mfloat-abi hard -S -o - %s | FileCheck -check-prefix=CHECKASM %s
+// RUN: %clang_cc1 -emit-llvm -o - %s | FileCheck -check-prefix=CHECKGLOBALS %s
 
 int g0;
 // CHECKBASIC-DAG: @g0 = common global i32 0
@@ -88,3 +89,9 @@
 void test9_bar(void) { }
 void test9_zed(void) __attribute__((section("test")));
 void test9_zed(void) __attribute__((alias("test9_bar")));
+
+// Test that the alias gets its linkage from its declared qual type.
+// CHECKGLOBALS: @test10_foo = internal
+// CHECKGLOBALS-NOT: @test10_foo = dso_local
+int test10;
+static int test10_foo __attribute__((alias("test10")));
Index: clang/lib/CodeGen/CodeGenModule.cpp
===================================================================
--- clang/lib/CodeGen/CodeGenModule.cpp
+++ clang/lib/CodeGen/CodeGenModule.cpp
@@ -4363,17 +4363,22 @@
   // Create a reference to the named value.  This ensures that it is emitted
   // if a deferred decl.
   llvm::Constant *Aliasee;
-  if (isa<llvm::FunctionType>(DeclTy))
+  llvm::GlobalValue::LinkageTypes LT;
+  if (isa<llvm::FunctionType>(DeclTy)) {
     Aliasee = GetOrCreateLLVMFunction(AA->getAliasee(), DeclTy, GD,
                                       /*ForVTable=*/false);
-  else
+    LT = getFunctionLinkage(GD);
+  } else {
     Aliasee = GetOrCreateLLVMGlobal(AA->getAliasee(),
                                     llvm::PointerType::getUnqual(DeclTy),
                                     /*D=*/nullptr);
+    LT = getLLVMLinkageVarDefinition(cast<VarDecl>(GD.getDecl()),
+                                     D->getType().isConstQualified());
+  }
 
   // Create the new alias itself, but don't set a name yet.
-  auto *GA = llvm::GlobalAlias::create(
-      DeclTy, 0, llvm::Function::ExternalLinkage, "", Aliasee, &getModule());
+  auto *GA =
+      llvm::GlobalAlias::create(DeclTy, 0, LT, "", Aliasee, &getModule());
 
   if (Entry) {
     if (GA->getAliasee() == Entry) {


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