Tests & stronger guarantees for hidl_* pads.

- Test that pads are zero (for future proofing, also ran tests
  on original implementation and bugfix).
- Use -Wpadded so that compiler guarantees there aren't padding
  bits hiding elsewhere (there aren't)

Bug: 131356202
Test: libhidl_test
  (without fixes, with fixes, and with this CL)

Change-Id: Ib52a16015b0393c104cd984376328cb0da888b03
Merged-In: Ib52a16015b0393c104cd984376328cb0da888b03

2 files changed, 24 insertions, 23 deletions

diff --git a/base/HidlSupport.cpp b/base/HidlSupport.cpp
index f97f216..af805b9 100644
--- a/base/HidlSupport.cpp
+++ b/base/HidlSupport.cpp
@@ -35,10 +35,8 @@ bool debuggable() {
 }
 }  // namespace details
 
-hidl_handle::hidl_handle() {
-    memset(this, 0, sizeof(*this));
-    // mHandle = nullptr;
-    // mOwnsHandle = false;
+hidl_handle::hidl_handle() : mHandle(nullptr), mOwnsHandle(false) {
+    memset(mPad, 0, sizeof(mPad));
 }
 
 hidl_handle::~hidl_handle() {
@@ -138,11 +136,8 @@ void hidl_handle::freeHandle() {
 
 static const char *const kEmptyString = "";
 
-hidl_string::hidl_string() {
-    memset(this, 0, sizeof(*this));
-    // mSize is zero
-    // mOwnsBuffer is false
-    mBuffer = kEmptyString;
+hidl_string::hidl_string() : mBuffer(kEmptyString), mSize(0), mOwnsBuffer(false) {
+    memset(mPad, 0, sizeof(mPad));
 }
 
 hidl_string::~hidl_string() {
diff --git a/base/include/hidl/HidlSupport.h b/base/include/hidl/HidlSupport.h
index 89aa5a9..71448da 100644
--- a/base/include/hidl/HidlSupport.h
+++ b/base/include/hidl/HidlSupport.h
@@ -20,18 +20,24 @@
 #include <algorithm>
 #include <array>
 #include <iterator>
-#include <cutils/native_handle.h>
 #include <hidl/HidlInternal.h>
-#include <hidl/Status.h>
 #include <map>
 #include <sstream>
 #include <stddef.h>
 #include <tuple>
 #include <type_traits>
+#include <vector>
+
+// no requirements on types not used in scatter/gather
+// no requirements on other libraries
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Wpadded"
+#include <cutils/native_handle.h>
+#include <hidl/Status.h>
 #include <utils/Errors.h>
 #include <utils/RefBase.h>
 #include <utils/StrongPointer.h>
-#include <vector>
+#pragma clang diagnostic pop
 
 namespace android {
 
@@ -123,8 +129,9 @@ struct hidl_handle {
 private:
     void freeHandle();
 
-    details::hidl_pointer<const native_handle_t> mHandle __attribute__ ((aligned(8)));
-    bool mOwnsHandle __attribute ((aligned(8)));
+    details::hidl_pointer<const native_handle_t> mHandle;
+    bool mOwnsHandle;
+    uint8_t mPad[7];
 };
 
 struct hidl_string {
@@ -174,6 +181,7 @@ private:
     details::hidl_pointer<const char> mBuffer;
     uint32_t mSize;  // NOT including the terminating '\0'.
     bool mOwnsBuffer; // if true then mBuffer is a mutable char *
+    uint8_t mPad[3];
 
     // copy from data with size. Assume that my memory is freed
     // (through clear(), for example)
@@ -294,9 +302,9 @@ struct hidl_memory {
     static const size_t kOffsetOfName;
 
 private:
-    hidl_handle mHandle __attribute__ ((aligned(8)));
-    uint64_t mSize __attribute__ ((aligned(8)));
-    hidl_string mName __attribute__ ((aligned(8)));
+    hidl_handle mHandle;
+    uint64_t mSize;
+    hidl_string mName;
 };
 
 // HidlMemory is a wrapper class to support sp<> for hidl_memory. It also
@@ -328,15 +336,12 @@ template<typename T>
 struct hidl_vec {
     using value_type = T;
 
-    hidl_vec() {
+    hidl_vec() : mBuffer(nullptr), mSize(0), mOwnsBuffer(true) {
         static_assert(hidl_vec<T>::kOffsetOfBuffer == 0, "wrong offset");
 
-        memset(this, 0, sizeof(*this));
-        // mSize is 0
-        // mBuffer is nullptr
+        // mOwnsBuffer true to match original implementation
 
-        // this is for consistency with the original implementation
-        mOwnsBuffer = true;
+        memset(mPad, 0, sizeof(mPad));
     }
 
     // Note, does not initialize primitive types.
@@ -581,6 +586,7 @@ public:
     details::hidl_pointer<T> mBuffer;
     uint32_t mSize;
     bool mOwnsBuffer;
+    uint8_t mPad[3];
 
     // copy from an array-like object, assuming my resources are freed.
     template <typename Array>