kinect_upload_fw: fix a -Wstrict-aliasing warning

kinect_upload_fw.c:87:2: warning: dereferencing type-punned pointer will break strict-aliasing rules [-Wstrict-aliasing]

Use a union when there is the need to use the same memory for variables
of incompatible types (especially if they have different storage size).

diff --git a/kinect_upload_fw/kinect_upload_fw.c b/kinect_upload_fw/kinect_upload_fw.c
index da909d5..51ef81e 100644 (file)
--- a/kinect_upload_fw/kinect_upload_fw.c
+++ b/kinect_upload_fw/kinect_upload_fw.c
@@ -83,31 +83,37 @@ static int get_first_reply(void) {
 }
 
 static int get_reply(void) {
-       unsigned char dump[512];
-       status_code buffer = ((status_code*)dump)[0];
+       union {
+               status_code buffer;
+               /* The following is needed because libusb_bulk_transfer might
+                * fail when working on a buffer smaller than 512 bytes.
+                */
+               unsigned char dump[512];
+       } reply;
        int res;
        int transferred;
-       res = libusb_bulk_transfer(dev, 0x81, (unsigned char*)&buffer, 512, &transferred, 0);
+
+       res = libusb_bulk_transfer(dev, 0x81, reply.dump, 512, &transferred, 0);
        if(res != 0 || transferred != sizeof(status_code)) {
                LOG("Error reading reply: %d\ttransferred: %d (expected %lu)\n", res, transferred, sizeof(status_code));
                return res;
        }
-       if(fn_le32(buffer.magic) != 0x0a6fe000) {
-               LOG("Error reading reply: invalid magic %08X\n",buffer.magic);
+       if(fn_le32(reply.buffer.magic) != 0x0a6fe000) {
+               LOG("Error reading reply: invalid magic %08X\n", reply.buffer.magic);
                return -1;
        }
-       if(fn_le32(buffer.seq) != seq) {
-               LOG("Error reading reply: non-matching sequence number %08X (expected %08X)\n", buffer.seq, seq);
+       if(fn_le32(reply.buffer.seq) != seq) {
+               LOG("Error reading reply: non-matching sequence number %08X (expected %08X)\n", reply.buffer.seq, seq);
                return -1;
        }
-       if(fn_le32(buffer.status) != 0) {
-               LOG("Notice reading reply: last uint32_t was nonzero: %d\n", buffer.status);
+       if(fn_le32(reply.buffer.status) != 0) {
+               LOG("Notice reading reply: last uint32_t was nonzero: %d\n", reply.buffer.status);
        }
 
        LOG("Reading reply: ");
        int i;
        for(i = 0; i < transferred; ++i) {
-               LOG("%02X ", ((unsigned char*)(&buffer))[i]);
+               LOG("%02X ", reply.dump[i]);
        }
        LOG("\n");