[libcamera-devel] [PATCH] libcamera: object: Silence gcc false positive error in release mode

[Laurent Pinchart]

gcc 10 and 11 produce an error when compiling libcamera in release mode:

In file included from ../../src/libcamera/base/object.cpp:13:
../../include/libcamera/base/message.h: In member function ‘void libcamera::Object::notifyThreadMove()’:
../../include/libcamera/base/message.h:58:47: error: array subscript ‘const libcamera::InvokeMessage[0]’ is partly outside array bounds of ‘libcamera::Message [1]’ [-Werror=array-bounds]
   58 |         Semaphore *semaphore() const { return semaphore_; }
      |                                               ^~~~~~~~~~
../../src/libcamera/base/object.cpp:280:17: note: while referencing ‘msg’
  280 |         Message msg(Message::ThreadMoveMessage);
      |                 ^~~

This seems to be a false positive, given that msg->type() can never be
equal to Message::InvokeMessage in Object::message() when called from
Object::notifyThreadMove(), as the message is created there with the
Message::ThreadMoveMessage type. The problem as been reported in
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105400, but the error
nonetheless needs to be fixed without waiting for a new gcc release, and
a dynamic_cast does the job with a small additional runtime cost that
shouldn't be a big issue, given that moving objects between threads is a
rare operation.

Bug: https://bugs.libcamera.org/show_bug.cgi?id=125
Signed-off-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>
---
 src/libcamera/base/object.cpp | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/src/libcamera/base/object.cpp b/src/libcamera/base/object.cpp
index ec5b55d125d1..92cecd22fbe9 100644
--- a/src/libcamera/base/object.cpp
+++ b/src/libcamera/base/object.cpp
@@ -189,7 +189,11 @@ void Object::message(Message *msg)
 {
 	switch (msg->type()) {
 	case Message::InvokeMessage: {
-		InvokeMessage *iMsg = static_cast<InvokeMessage *>(msg);
+		/*
+		 * A static_cast should be enough, but gcc 10 and 11 choke on
+		 * it in release mode (with -O2 or -O3).
+		 */
+		InvokeMessage *iMsg = dynamic_cast<InvokeMessage *>(msg);
 		Semaphore *semaphore = iMsg->semaphore();
 		iMsg->invoke();
 
-- 
Regards,

Laurent Pinchart