From 148d90729e9fa132f170ba0627bcfb9ee90a0f38 Mon Sep 17 00:00:00 2001 From: Fangrui Song Date: Mon, 15 Jul 2024 11:27:01 -0700 Subject: [CodeGen] Set attributes on resolvers emitted after ifuncs Visiting the ifunc calls `GetOrCreateLLVMFunction` with `NotForDefinition` while visiting the resolver calls `GetOrCreateLLVMFunction` with `ForDefinition`. When an ifunc is emitted before its resolver, the `ForDefinition` call does not call `SetFunctionAttributes`, because the function prematurely returns due to `(Entry->getValueType() == Ty)` and `llvm::GlobalIFunc::getResolverFunctionType(DeclTy)`. This leads to missing `!kcfi_type` with -fsanitize=kcfi. ``` extern void ifunc0(void) __attribute__ ((ifunc("resolver0"))); void *resolver0(void) { return 0; } // SetFunctionAttributes not called extern void ifunc1(void) __attribute__ ((ifunc("resolver1"))); static void *resolver1(void) { return 0; } // SetFunctionAttributes not called extern void ifunc2(void) __attribute__ ((ifunc("resolver2"))); static void *resolver2(void*) { return 0; } ``` Ensure `SetFunctionAttributes` is called by calling `GetOrCreateLLVMFunction` with a dummy non-function type. Now that the `F->takeName(Entry)` code path may be taken, the `DisableSanitizerInstrumentation` code (https://reviews.llvm.org/D150262) should be moved to `checkAliases`, when the resolver function is finalized. Pull Request: https://github.com/llvm/llvm-project/pull/98832 --- clang/lib/CodeGen/CodeGenModule.cpp | 17 +++++++++++------ 1 file changed, 11 insertions(+), 6 deletions(-) (limited to 'clang/lib/CodeGen/CodeGenModule.cpp') diff --git a/clang/lib/CodeGen/CodeGenModule.cpp b/clang/lib/CodeGen/CodeGenModule.cpp index 08cfa69..ee05cdd 100644 --- a/clang/lib/CodeGen/CodeGenModule.cpp +++ b/clang/lib/CodeGen/CodeGenModule.cpp @@ -721,6 +721,11 @@ void CodeGenModule::checkAliases() { cast(Alias)->setAliasee(Aliasee); } } + // ifunc resolvers are usually implemented to run before sanitizer + // initialization. Disable instrumentation to prevent the ordering issue. + if (IsIFunc) + cast(Aliasee)->addFnAttr( + llvm::Attribute::DisableSanitizerInstrumentation); } if (!Error) return; @@ -6106,11 +6111,14 @@ void CodeGenModule::emitIFuncDefinition(GlobalDecl GD) { Aliases.push_back(GD); - llvm::Type *DeclTy = getTypes().ConvertTypeForMem(D->getType()); - llvm::Type *ResolverTy = llvm::GlobalIFunc::getResolverFunctionType(DeclTy); + // The resolver might not be visited yet. Specify a dummy non-function type to + // indicate IsIncompleteFunction. Either the type is ignored (if the resolver + // was emitted) or the whole function will be replaced (if the resolver has + // not been emitted). llvm::Constant *Resolver = - GetOrCreateLLVMFunction(IFA->getResolver(), ResolverTy, {}, + GetOrCreateLLVMFunction(IFA->getResolver(), VoidTy, {}, /*ForVTable=*/false); + llvm::Type *DeclTy = getTypes().ConvertTypeForMem(D->getType()); llvm::GlobalIFunc *GIF = llvm::GlobalIFunc::create(DeclTy, 0, llvm::Function::ExternalLinkage, "", Resolver, &getModule()); @@ -6134,9 +6142,6 @@ void CodeGenModule::emitIFuncDefinition(GlobalDecl GD) { Entry->eraseFromParent(); } else GIF->setName(MangledName); - if (auto *F = dyn_cast(Resolver)) { - F->addFnAttr(llvm::Attribute::DisableSanitizerInstrumentation); - } SetCommonAttributes(GD, GIF); } -- cgit v1.1