[libcamera-devel] [PATCH] libcamera: controls: Fix strict aliasing violation

[Laurent Pinchart]

gcc 8.3.0 for ARM complains about strict aliasing violations:

../../src/libcamera/controls.cpp: In member function ‘void libcamera::ControlValue::release()’:
../../src/libcamera/controls.cpp:111:13: error: dereferencing type-punned pointer will break strict-aliasing rules [-Werror=strict-aliasing]
   delete[] *reinterpret_cast<char **>(&storage_);

Fix it and simplify the code at the same time.

Signed-off-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>
---
 include/libcamera/controls.h |  5 ++++-
 src/libcamera/controls.cpp   | 20 ++++++++++----------
 2 files changed, 14 insertions(+), 11 deletions(-)

diff --git a/include/libcamera/controls.h b/include/libcamera/controls.h
index 4767e2d3fc8c..0e111ab72bce 100644
--- a/include/libcamera/controls.h
+++ b/include/libcamera/controls.h
@@ -160,7 +160,10 @@ private:
 	ControlType type_ : 8;
 	bool isArray_ : 1;
 	std::size_t numElements_ : 16;
-	uint64_t storage_;
+	union {
+		uint64_t value_;
+		void *storage_;
+	};
 
 	void release();
 	void set(ControlType type, bool isArray, const void *data,
diff --git a/src/libcamera/controls.cpp b/src/libcamera/controls.cpp
index 94bdbdd9c388..4326174adf86 100644
--- a/src/libcamera/controls.cpp
+++ b/src/libcamera/controls.cpp
@@ -107,9 +107,9 @@ void ControlValue::release()
 {
 	std::size_t size = numElements_ * ControlValueSize[type_];
 
-	if (size > sizeof(storage_)) {
-		delete[] *reinterpret_cast<char **>(&storage_);
-		storage_ = 0;
+	if (size > sizeof(value_)) {
+		delete[] reinterpret_cast<uint8_t *>(storage_);
+		storage_ = nullptr;
 	}
 }
 
@@ -176,9 +176,9 @@ ControlValue &ControlValue::operator=(const ControlValue &other)
 Span<const uint8_t> ControlValue::data() const
 {
 	std::size_t size = numElements_ * ControlValueSize[type_];
-	const uint8_t *data = size > sizeof(storage_)
-			    ? *reinterpret_cast<const uint8_t * const *>(&storage_)
-			    : reinterpret_cast<const uint8_t *>(&storage_);
+	const uint8_t *data = size > sizeof(value_)
+			    ? reinterpret_cast<const uint8_t *>(storage_)
+			    : reinterpret_cast<const uint8_t *>(&value_);
 	return { data, size };
 }
 
@@ -308,11 +308,11 @@ void ControlValue::set(ControlType type, bool isArray, const void *data,
 	std::size_t size = elementSize * numElements;
 	void *storage;
 
-	if (size > sizeof(storage_)) {
-		storage = reinterpret_cast<void *>(new char[size]);
-		*reinterpret_cast<void **>(&storage_) = storage;
+	if (size > sizeof(value_)) {
+		storage_ = reinterpret_cast<void *>(new uint8_t[size]);
+		storage = storage_;
 	} else {
-		storage = reinterpret_cast<void *>(&storage_);
+		storage = reinterpret_cast<void *>(&value_);
 	}
 
 	memcpy(storage, data, size);
-- 
Regards,

Laurent Pinchart