[PATCH] D112868: [Sema] Diagnose and reject non-function ifunc resolvers

[Itay Bookstein via Phabricator via cfe-commits]

ibookstein created this revision.
ibookstein added reviewers: MaskRay, aaron.ballman.
ibookstein requested review of this revision.
Herald added a project: clang.
Herald added a subscriber: cfe-commits.

Signed-off-by: Itay Bookstein <ibookst...@gmail.com>


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D112868

Files:
  clang/lib/CodeGen/CodeGenModule.cpp
  clang/test/Sema/attr-ifunc.c


Index: clang/test/Sema/attr-ifunc.c
===================================================================
--- clang/test/Sema/attr-ifunc.c
+++ clang/test/Sema/attr-ifunc.c
@@ -13,8 +13,7 @@
 void f1() __attribute__((ifunc("f1_ifunc")));
 //expected-error@-1 {{ifunc must point to a defined function}}
 
-void* f2_a() __attribute__((ifunc("f2_b")));
-//expected-error@-1 {{ifunc definition is part of a cycle}}
+void* f2_a() __attribute__((alias("f2_b")));
 void* f2_b() __attribute__((ifunc("f2_a")));
 //expected-error@-1 {{ifunc definition is part of a cycle}}
 
@@ -27,6 +26,15 @@
 void f4() __attribute__((ifunc("f4_ifunc")));
 //expected-error@-1 {{ifunc resolver function must return a pointer}}
 
+int f5_resolver_gvar;
+void f5() __attribute__((ifunc("f5_resolver_gvar")));
+//expected-error@-1 {{ifunc must point to a defined function}}
+
+void *f6_resolver_resolver() { return 0; }
+void *f6_resolver() __attribute__((ifunc("f6_resolver_resolver")));
+void f6() __attribute__((ifunc("f6_resolver")));
+//expected-error@-1 {{ifunc must point to a defined function}}
+
 #else
 void f1a() __asm("f1");
 void f1a() {}
Index: clang/lib/CodeGen/CodeGenModule.cpp
===================================================================
--- clang/lib/CodeGen/CodeGenModule.cpp
+++ clang/lib/CodeGen/CodeGenModule.cpp
@@ -318,21 +318,58 @@
 // This is only used in aliases that we created and we know they have a
 // linear structure.
 static const llvm::GlobalValue *getAliasedGlobal(const llvm::GlobalValue *GV) {
-  llvm::SmallPtrSet<const llvm::GlobalValue *, 4> Visited;
-  for (;;) {
-    if (!GV || !Visited.insert(GV).second)
-      return nullptr;
-
-    const llvm::Constant *C;
-    if (auto *GA = dyn_cast<llvm::GlobalAlias>(GV))
-      C = GA->getAliasee();
-    else if (auto *GI = dyn_cast<llvm::GlobalIFunc>(GV))
-      C = GI->getResolver();
-    else
-      return GV;
+  const llvm::Constant *C;
+  if (auto *GA = dyn_cast<llvm::GlobalAlias>(GV))
+    C = GA->getAliasee();
+  else if (auto *GI = dyn_cast<llvm::GlobalIFunc>(GV))
+    C = GI->getResolver();
+  else
+    return GV;
+
+  const auto *AliaseeGV = dyn_cast<llvm::GlobalValue>(C->stripPointerCasts());
+  if (!AliaseeGV)
+    return nullptr;
+
+  const llvm::GlobalValue *FinalGV = AliaseeGV->getAliaseeObject();
+  if (FinalGV == GV)
+    return nullptr;
+
+  return FinalGV;
+}
+
+static bool checkAliasedGlobal(const llvm::GlobalValue *Alias,
+                               DiagnosticsEngine &Diags,
+                               SourceLocation Location,
+                               const llvm::GlobalValue *&GV) {
+  bool IsIFunc = isa<llvm::GlobalIFunc>(Alias);
+  GV = getAliasedGlobal(Alias);
+  if (!GV) {
+    Diags.Report(Location, diag::err_cyclic_alias) << IsIFunc;
+    return false;
+  }
+
+  if (GV->isDeclaration()) {
+    Diags.Report(Location, diag::err_alias_to_undefined) << IsIFunc << IsIFunc;
+    return false;
+  }
+
+  if (IsIFunc) {
+    // Check resolver function type.
+    const auto *F = dyn_cast<llvm::Function>(GV);
+    if (!F) {
+      Diags.Report(Location, diag::err_alias_to_undefined)
+          << IsIFunc << IsIFunc;
+      return false;
+    }
 
-    GV = dyn_cast<llvm::GlobalValue>(C->stripPointerCasts());
+    llvm::FunctionType *FTy = F->getFunctionType();
+    if (!FTy->getReturnType()->isPointerTy()) {
+      Diags.Report(Location, diag::err_ifunc_resolver_return);
+      return false;
+    }
   }
+
+  return true;
 }
 
 void CodeGenModule::checkAliases() {
@@ -344,30 +381,20 @@
   for (const GlobalDecl &GD : Aliases) {
     const auto *D = cast<ValueDecl>(GD.getDecl());
     SourceLocation Location;
-    bool IsIFunc = D->hasAttr<IFuncAttr>();
     if (const Attr *A = D->getDefiningAttr())
       Location = A->getLocation();
     else
       llvm_unreachable("Not an alias or ifunc?");
+
     StringRef MangledName = getMangledName(GD);
     llvm::GlobalValue *Alias = GetGlobalValue(MangledName);
-    const llvm::GlobalValue *GV = getAliasedGlobal(Alias);
-    if (!GV) {
-      Error = true;
-      Diags.Report(Location, diag::err_cyclic_alias) << IsIFunc;
-    } else if (GV->isDeclaration()) {
+    const llvm::GlobalValue *GV = nullptr;
+    if (!checkAliasedGlobal(Alias, Diags, Location, GV)) {
       Error = true;
-      Diags.Report(Location, diag::err_alias_to_undefined)
-          << IsIFunc << IsIFunc;
-    } else if (IsIFunc) {
-      // Check resolver function type.
-      llvm::FunctionType *FTy = dyn_cast<llvm::FunctionType>(
-          GV->getType()->getPointerElementType());
-      assert(FTy);
-      if (!FTy->getReturnType()->isPointerTy())
-        Diags.Report(Location, diag::err_ifunc_resolver_return);
+      continue;
     }
 
+    bool IsIFunc = isa<llvm::GlobalIFunc>(Alias);
     llvm::Constant *Aliasee =
         IsIFunc ? cast<llvm::GlobalIFunc>(Alias)->getResolver()
                 : cast<llvm::GlobalAlias>(Alias)->getAliasee();

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