From 511ad6492eabb7797910ce8689577c45f57bce40 Mon Sep 17 00:00:00 2001
From: Derek Mauro <dmauro@google.com>
Date: Tue, 25 Jul 2023 13:04:25 -0700
Subject: InlinedVector: Fix control-flow-inregrity warning when using a class
 with a vtable

The code is getting the pointer, then constructing it on the next
line. Using reinterpret_cast on this pointer is legal according to
https://clang.llvm.org/docs/ControlFlowIntegrity.html#bad-cast-checking,
but it flags it anyway. The docs say it might be necessary for
`allocate()`-type APIs, and recommends adding them to an ignorelist.

Also note that std::addressof is removed. It is unnecessary since
inlined_data is a char-array.

PiperOrigin-RevId: 550972834
Change-Id: Ib224cec330bb6bcb770296de6c91881f404ef531
---
 absl/base/attributes.h                   |  2 +-
 absl/container/inlined_vector_test.cc    |  5 +++++
 absl/container/internal/inlined_vector.h | 19 ++++++++++++++-----
 3 files changed, 20 insertions(+), 6 deletions(-)

diff --git a/absl/base/attributes.h b/absl/base/attributes.h
index cb3f367f..a7f279a0 100644
--- a/absl/base/attributes.h
+++ b/absl/base/attributes.h
@@ -274,7 +274,7 @@
 //
 // Tells the ControlFlowIntegrity sanitizer to not instrument a given function.
 // See https://clang.llvm.org/docs/ControlFlowIntegrity.html for details.
-#if ABSL_HAVE_ATTRIBUTE(no_sanitize)
+#if ABSL_HAVE_ATTRIBUTE(no_sanitize) && defined(__llvm__)
 #define ABSL_ATTRIBUTE_NO_SANITIZE_CFI __attribute__((no_sanitize("cfi")))
 #else
 #define ABSL_ATTRIBUTE_NO_SANITIZE_CFI
diff --git a/absl/container/inlined_vector_test.cc b/absl/container/inlined_vector_test.cc
index 6f4625dc..07304518 100644
--- a/absl/container/inlined_vector_test.cc
+++ b/absl/container/inlined_vector_test.cc
@@ -1621,6 +1621,11 @@ TEST(DynamicVec, DynamicVecCompiles) {
   (void)v;
 }
 
+TEST(DynamicVec, CreateNonEmptyDynamicVec) {
+  DynamicVec v(1);
+  EXPECT_EQ(v.size(), 1u);
+}
+
 TEST(AllocatorSupportTest, Constructors) {
   using MyAlloc = CountingAllocator<int>;
   using AllocVec = absl::InlinedVector<int, 4, MyAlloc>;
diff --git a/absl/container/internal/inlined_vector.h b/absl/container/internal/inlined_vector.h
index f886dfa0..639bf145 100644
--- a/absl/container/internal/inlined_vector.h
+++ b/absl/container/internal/inlined_vector.h
@@ -391,13 +391,22 @@ class Storage {
   }
 
   Pointer<A> GetInlinedData() {
-    return reinterpret_cast<Pointer<A>>(
-        std::addressof(data_.inlined.inlined_data[0]));
+    return reinterpret_cast<Pointer<A>>(data_.inlined.inlined_data);
   }
 
   ConstPointer<A> GetInlinedData() const {
-    return reinterpret_cast<ConstPointer<A>>(
-        std::addressof(data_.inlined.inlined_data[0]));
+    return reinterpret_cast<ConstPointer<A>>(data_.inlined.inlined_data);
+  }
+
+  // Like GetInlinedData(), but for data that has not been constructed yet.  The
+  // only difference is ABSL_ATTRIBUTE_NO_SANITIZE_CFI, which is necessary
+  // because the object is uninitialized.
+  // https://clang.llvm.org/docs/ControlFlowIntegrity.html#bad-cast-checking
+  // NOTE: When this was written, LLVM documentation did not explicitly
+  // mention that casting `char*` and using `reinterpret_cast` qualifies
+  // as a bad cast.
+  ABSL_ATTRIBUTE_NO_SANITIZE_CFI Pointer<A> GetInlinedDataUninitialized() {
+    return reinterpret_cast<Pointer<A>>(data_.inlined.inlined_data);
   }
 
   SizeType<A> GetAllocatedCapacity() const {
@@ -628,7 +637,7 @@ auto Storage<T, N, A>::Initialize(ValueAdapter values, SizeType<A> new_size)
     SetAllocation(allocation);
     SetIsAllocated();
   } else {
-    construct_data = GetInlinedData();
+    construct_data = GetInlinedDataUninitialized();
   }
 
   ConstructElements<A>(GetAllocator(), construct_data, values, new_size);
-- 
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