Minimal runtime for UBSan.

Summary:
An implementation of ubsan runtime library suitable for use in production.

Minimal attack surface.
* No stack traces.
* Definitely no C++ demangling.
* No UBSAN_OPTIONS=log_file=/path (very suid-unfriendly). And no UBSAN_OPTIONS in general.
* as simple as possible

Minimal CPU and RAM overhead.
* Source locations unnecessary in the presence of (split) debug info.
* Values and types (as in A+B overflows T) can be reconstructed from register/stack dumps, once you know what type of error you are looking at.
* above two items save 3% binary size.

When UBSan is used with -ftrap-function=abort, sometimes it is hard to reason about failures. This library replaces abort with a slightly more informative message without much extra overhead. Since ubsan interface in not stable, this code must reside in compiler-rt.

Reviewers: pcc, kcc

Subscribers: srhines, mgorny, aprantl, krytarowski, llvm-commits

Differential Revision: https://reviews.llvm.org/D36810

llvm-svn: 312029

1 files changed, 27 insertions, 22 deletions

diff --git a/clang/lib/CodeGen/CGExpr.cpp b/clang/lib/CodeGen/CGExpr.cpp
index 5f8f34e9bcc..bff3fcf6db2 100644
--- a/clang/lib/CodeGen/CGExpr.cpp
+++ b/clang/lib/CodeGen/CGExpr.cpp
@@ -2724,13 +2724,16 @@ static void emitCheckHandlerCall(CodeGenFunction &CGF,
   assert(IsFatal || RecoverKind != CheckRecoverableKind::Unrecoverable);
   bool NeedsAbortSuffix =
       IsFatal && RecoverKind != CheckRecoverableKind::Unrecoverable;
+  bool MinimalRuntime = CGF.CGM.getCodeGenOpts().SanitizeMinimalRuntime;
   const SanitizerHandlerInfo &CheckInfo = SanitizerHandlers[CheckHandler];
   const StringRef CheckName = CheckInfo.Name;
-  std::string FnName =
-      ("__ubsan_handle_" + CheckName +
-       (CheckInfo.Version ? "_v" + llvm::utostr(CheckInfo.Version) : "") +
-       (NeedsAbortSuffix ? "_abort" : ""))
-          .str();
+  std::string FnName = "__ubsan_handle_" + CheckName.str();
+  if (CheckInfo.Version && !MinimalRuntime)
+    FnName += "_v" + llvm::utostr(CheckInfo.Version);
+  if (MinimalRuntime)
+    FnName += "_minimal";
+  if (NeedsAbortSuffix)
+    FnName += "_abort";
   bool MayReturn =
       !IsFatal || RecoverKind == CheckRecoverableKind::AlwaysRecoverable;
 
@@ -2817,24 +2820,26 @@ void CodeGenFunction::EmitCheck(
   // representing operand values.
   SmallVector<llvm::Value *, 4> Args;
   SmallVector<llvm::Type *, 4> ArgTypes;
-  Args.reserve(DynamicArgs.size() + 1);
-  ArgTypes.reserve(DynamicArgs.size() + 1);
-
-  // Emit handler arguments and create handler function type.
-  if (!StaticArgs.empty()) {
-    llvm::Constant *Info = llvm::ConstantStruct::getAnon(StaticArgs);
-    auto *InfoPtr =
-        new llvm::GlobalVariable(CGM.getModule(), Info->getType(), false,
-                                 llvm::GlobalVariable::PrivateLinkage, Info);
-    InfoPtr->setUnnamedAddr(llvm::GlobalValue::UnnamedAddr::Global);
-    CGM.getSanitizerMetadata()->disableSanitizerForGlobal(InfoPtr);
-    Args.push_back(Builder.CreateBitCast(InfoPtr, Int8PtrTy));
-    ArgTypes.push_back(Int8PtrTy);
-  }
+  if (!CGM.getCodeGenOpts().SanitizeMinimalRuntime) {
+    Args.reserve(DynamicArgs.size() + 1);
+    ArgTypes.reserve(DynamicArgs.size() + 1);
+
+    // Emit handler arguments and create handler function type.
+    if (!StaticArgs.empty()) {
+      llvm::Constant *Info = llvm::ConstantStruct::getAnon(StaticArgs);
+      auto *InfoPtr =
+          new llvm::GlobalVariable(CGM.getModule(), Info->getType(), false,
+                                   llvm::GlobalVariable::PrivateLinkage, Info);
+      InfoPtr->setUnnamedAddr(llvm::GlobalValue::UnnamedAddr::Global);
+      CGM.getSanitizerMetadata()->disableSanitizerForGlobal(InfoPtr);
+      Args.push_back(Builder.CreateBitCast(InfoPtr, Int8PtrTy));
+      ArgTypes.push_back(Int8PtrTy);
+    }
 
-  for (size_t i = 0, n = DynamicArgs.size(); i != n; ++i) {
-    Args.push_back(EmitCheckValue(DynamicArgs[i]));
-    ArgTypes.push_back(IntPtrTy);
+    for (size_t i = 0, n = DynamicArgs.size(); i != n; ++i) {
+      Args.push_back(EmitCheckValue(DynamicArgs[i]));
+      ArgTypes.push_back(IntPtrTy);
+    }
   }
 
   llvm::FunctionType *FnType =