[PATCH 2/2] options: Replace use of VLAs in C++

[Laurent Pinchart]

Hi Khem,

Thank you for the patch.

On Wed, Jan 31, 2024 at 09:08:10PM -0800, Khem Raj wrote:
> Clang++ 18 is fussy about this with new warning checks.
> 
>    ../git/src/apps/common/options.cpp:882:20: error: variable length arrays in C++ are a Clang extension [-Werror,-Wvla-cxx-extension]
>       882 |         char shortOptions[optionsMap_.size() * 3 + 2];
>           |                           ^~~~~~~~~~~~~~~~~~~~~~~~~~
> 
> Therefore replace using VLAs with alloca and malloc/free
> 
> Signed-off-by: Khem Raj <raj.khem at gmail.com>
> ---
>  src/apps/common/options.cpp      |  4 ++--
>  src/libcamera/ipc_unixsocket.cpp | 12 ++++++++----
>  2 files changed, 10 insertions(+), 6 deletions(-)
> 
> diff --git a/src/apps/common/options.cpp b/src/apps/common/options.cpp
> index 4f7e8691..b020f603 100644
> --- a/src/apps/common/options.cpp
> +++ b/src/apps/common/options.cpp
> @@ -879,8 +879,8 @@ OptionsParser::Options OptionsParser::parse(int argc, char **argv)
>  	 * Allocate short and long options arrays large enough to contain all
>  	 * options.
>  	 */
> -	char shortOptions[optionsMap_.size() * 3 + 2];
> -	struct option longOptions[optionsMap_.size() + 1];
> +	char *shortOptions = (char*)alloca(optionsMap_.size() * 3 + 2);

We use C++ casts for C++ code.

> +	struct option *longOptions = (struct option*)alloca(optionsMap_.size() + 1);
>  	unsigned int ids = 0;
>  	unsigned int idl = 0;
>  
> diff --git a/src/libcamera/ipc_unixsocket.cpp b/src/libcamera/ipc_unixsocket.cpp
> index 1980d374..3a7f8ee6 100644
> --- a/src/libcamera/ipc_unixsocket.cpp
> +++ b/src/libcamera/ipc_unixsocket.cpp
> @@ -247,8 +247,8 @@ int IPCUnixSocket::sendData(const void *buffer, size_t length,
>  	iov[0].iov_base = const_cast<void *>(buffer);
>  	iov[0].iov_len = length;
>  
> -	char buf[CMSG_SPACE(num * sizeof(uint32_t))];
> -	memset(buf, 0, sizeof(buf));
> +	char *buf = (char*)malloc(CMSG_SPACE(num * sizeof(uint32_t)));

Why do you allocate on the heap here while you allocate on the stack
above ?

> +	memset((void*)buf, 0, sizeof(buf));
>  
>  	struct cmsghdr *cmsg = (struct cmsghdr *)buf;
>  	cmsg->cmsg_len = CMSG_LEN(num * sizeof(uint32_t));
> @@ -270,9 +270,11 @@ int IPCUnixSocket::sendData(const void *buffer, size_t length,
>  		int ret = -errno;
>  		LOG(IPCUnixSocket, Error)
>  			<< "Failed to sendmsg: " << strerror(-ret);
> +    free(buf);

Did you run checkstyle.py ?

free() is error-prone. You should use a C++ class that provides RAII
instead of freeing memory manually.

>  		return ret;
>  	}
>  
> +  free(buf);
>  	return 0;
>  }
>  
> @@ -283,8 +285,8 @@ int IPCUnixSocket::recvData(void *buffer, size_t length,
>  	iov[0].iov_base = buffer;
>  	iov[0].iov_len = length;
>  
> -	char buf[CMSG_SPACE(num * sizeof(uint32_t))];
> -	memset(buf, 0, sizeof(buf));
> +	char *buf = (char*)malloc(CMSG_SPACE(num * sizeof(uint32_t)));
> +	memset((void*)buf, 0, sizeof(buf));
>  
>  	struct cmsghdr *cmsg = (struct cmsghdr *)buf;
>  	cmsg->cmsg_len = CMSG_LEN(num * sizeof(uint32_t));
> @@ -305,12 +307,14 @@ int IPCUnixSocket::recvData(void *buffer, size_t length,
>  		if (ret != -EAGAIN)
>  			LOG(IPCUnixSocket, Error)
>  				<< "Failed to recvmsg: " << strerror(-ret);
> +    free(buf);
>  		return ret;
>  	}
>  
>  	if (fds)
>  		memcpy(fds, CMSG_DATA(cmsg), num * sizeof(uint32_t));
>  
> +  free(buf);
>  	return 0;
>  }
>  

-- 
Regards,

Laurent Pinchart