--- tools/qemu-xen-traditional/hw/fdc.c.orig	2014-10-06 15:50:24 UTC
+++ tools/qemu-xen-traditional/hw/fdc.c
@@ -1318,7 +1318,7 @@ static uint32_t fdctrl_read_data (fdctrl
 {
     fdrive_t *cur_drv;
     uint32_t retval = 0;
-    int pos;
+    uint32_t pos;
 
     cur_drv = get_cur_drv(fdctrl);
     fdctrl->dsr &= ~FD_DSR_PWRDOWN;
@@ -1327,8 +1327,8 @@ static uint32_t fdctrl_read_data (fdctrl
         return 0;
     }
     pos = fdctrl->data_pos;
+    pos %= FD_SECTOR_LEN;
     if (fdctrl->msr & FD_MSR_NONDMA) {
-        pos %= FD_SECTOR_LEN;
         if (pos == 0) {
             if (fdctrl->data_pos != 0)
                 if (!fdctrl_seek_to_next_sect(fdctrl, cur_drv)) {
@@ -1673,10 +1673,13 @@ static void fdctrl_handle_option (fdctrl
 static void fdctrl_handle_drive_specification_command (fdctrl_t *fdctrl, int direction)
 {
     fdrive_t *cur_drv = get_cur_drv(fdctrl);
+    uint32_t pos;
 
-    if (fdctrl->fifo[fdctrl->data_pos - 1] & 0x80) {
+    pos = fdctrl->data_pos - 1;
+    pos %= FD_SECTOR_LEN;
+    if (fdctrl->fifo[pos] & 0x80) {
         /* Command parameters done */
-        if (fdctrl->fifo[fdctrl->data_pos - 1] & 0x40) {
+        if (fdctrl->fifo[pos] & 0x40) {
             fdctrl->fifo[0] = fdctrl->fifo[1];
             fdctrl->fifo[2] = 0;
             fdctrl->fifo[3] = 0;
@@ -1771,7 +1774,7 @@ static uint8_t command_to_handler[256];
 static void fdctrl_write_data (fdctrl_t *fdctrl, uint32_t value)
 {
     fdrive_t *cur_drv;
-    int pos;
+    uint32_t pos;
 
     /* Reset mode */
     if (!(fdctrl->dor & FD_DOR_nRESET)) {
@@ -1817,7 +1820,9 @@ static void fdctrl_write_data (fdctrl_t 
     }
 
     FLOPPY_DPRINTF("%s: %02x\n", __func__, value);
-    fdctrl->fifo[fdctrl->data_pos++] = value;
+    pos = fdctrl->data_pos++;
+    pos %= FD_SECTOR_LEN;
+    fdctrl->fifo[pos] = value;
     if (fdctrl->data_pos == fdctrl->data_len) {
         /* We now have all parameters
          * and will be able to treat the command
--- tools/qemu-xen/hw/block/fdc.c.orig	2014-12-02 10:41:02 UTC
+++ tools/qemu-xen/hw/block/fdc.c
@@ -1440,7 +1440,7 @@ static uint32_t fdctrl_read_data(FDCtrl 
 {
     FDrive *cur_drv;
     uint32_t retval = 0;
-    int pos;
+    uint32_t pos;
 
     cur_drv = get_cur_drv(fdctrl);
     fdctrl->dsr &= ~FD_DSR_PWRDOWN;
@@ -1449,8 +1449,8 @@ static uint32_t fdctrl_read_data(FDCtrl 
         return 0;
     }
     pos = fdctrl->data_pos;
+    pos %= FD_SECTOR_LEN;
     if (fdctrl->msr & FD_MSR_NONDMA) {
-        pos %= FD_SECTOR_LEN;
         if (pos == 0) {
             if (fdctrl->data_pos != 0)
                 if (!fdctrl_seek_to_next_sect(fdctrl, cur_drv)) {
@@ -1794,10 +1794,13 @@ static void fdctrl_handle_option(FDCtrl 
 static void fdctrl_handle_drive_specification_command(FDCtrl *fdctrl, int direction)
 {
     FDrive *cur_drv = get_cur_drv(fdctrl);
+    uint32_t pos;
 
-    if (fdctrl->fifo[fdctrl->data_pos - 1] & 0x80) {
+    pos = fdctrl->data_pos - 1;
+    pos %= FD_SECTOR_LEN;
+    if (fdctrl->fifo[pos] & 0x80) {
         /* Command parameters done */
-        if (fdctrl->fifo[fdctrl->data_pos - 1] & 0x40) {
+        if (fdctrl->fifo[pos] & 0x40) {
             fdctrl->fifo[0] = fdctrl->fifo[1];
             fdctrl->fifo[2] = 0;
             fdctrl->fifo[3] = 0;
@@ -1897,7 +1900,7 @@ static uint8_t command_to_handler[256];
 static void fdctrl_write_data(FDCtrl *fdctrl, uint32_t value)
 {
     FDrive *cur_drv;
-    int pos;
+    uint32_t pos;
 
     /* Reset mode */
     if (!(fdctrl->dor & FD_DOR_nRESET)) {
@@ -1945,7 +1948,9 @@ static void fdctrl_write_data(FDCtrl *fd
     }
 
     FLOPPY_DPRINTF("%s: %02x\n", __func__, value);
-    fdctrl->fifo[fdctrl->data_pos++] = value;
+    pos = fdctrl->data_pos++;
+    pos %= FD_SECTOR_LEN;
+    fdctrl->fifo[pos] = value;
     if (fdctrl->data_pos == fdctrl->data_len) {
         /* We now have all parameters
          * and will be able to treat the command