cpu_ioreq_pio, cpu_ioreq_move: introduce read_phys_req_item, write_phys_req_item

Replace a lot of formulaic multiplications (containing casts, no less)
with calls to a pair of functions.  This encapsulates in a single
place the operations which require care relating to integer overflow.

Cc: Dongxiao Xu <dongxiao.xu@intel.com>
Signed-off-by: Ian Jackson <ian.jackson@eu.citrix.com>
Acked-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>

xen-all.c

@@ -683,11 +683,45 @@ static void do_outp(pio_addr_t addr,
     }
 }
 
-static void cpu_ioreq_pio(ioreq_t *req)
+/*
+ * Helper functions which read/write an object from/to physical guest
+ * memory, as part of the implementation of an ioreq.
+ *
+ * Equivalent to
+ *   cpu_physical_memory_rw(addr + (req->df ? -1 : +1) * req->size * i,
+ *                          val, req->size, 0/1)
+ * except without the integer overflow problems.
+ */
+static void rw_phys_req_item(hwaddr addr,
+                             ioreq_t *req, uint32_t i, void *val, int rw)
+{
+    /* Do everything unsigned so overflow just results in a truncated result
+     * and accesses to undesired parts of guest memory, which is up
+     * to the guest */
+    hwaddr offset = (hwaddr)req->size * i;
+    if (req->df) {
+        addr -= offset;
+    } else {
+        addr += offset;
+    }
+    cpu_physical_memory_rw(addr, val, req->size, rw);
+}
+
+static inline void read_phys_req_item(hwaddr addr,
+                                      ioreq_t *req, uint32_t i, void *val)
 {
-    int i, sign;
+    rw_phys_req_item(addr, req, i, val, 0);
+}
+static inline void write_phys_req_item(hwaddr addr,
+                                       ioreq_t *req, uint32_t i, void *val)
+{
+    rw_phys_req_item(addr, req, i, val, 1);
+}
 
-    sign = req->df ? -1 : 1;
+
+static void cpu_ioreq_pio(ioreq_t *req)
+{
+    int i;
 
     if (req->dir == IOREQ_READ) {
         if (!req->data_is_ptr) {
@@ -697,9 +731,7 @@ static void cpu_ioreq_pio(ioreq_t *req)
 
             for (i = 0; i < req->count; i++) {
                 tmp = do_inp(req->addr, req->size);
-                cpu_physical_memory_write(
-                        req->data + (sign * i * (int64_t)req->size),
-                        (uint8_t *) &tmp, req->size);
+                write_phys_req_item(req->data, req, i, &tmp);
             }
         }
     } else if (req->dir == IOREQ_WRITE) {
@@ -709,9 +741,7 @@ static void cpu_ioreq_pio(ioreq_t *req)
             for (i = 0; i < req->count; i++) {
                 uint32_t tmp = 0;
 
-                cpu_physical_memory_read(
-                        req->data + (sign * i * (int64_t)req->size),
-                        (uint8_t*) &tmp, req->size);
+                read_phys_req_item(req->data, req, i, &tmp);
                 do_outp(req->addr, req->size, tmp);
             }
         }
@@ -720,22 +750,16 @@ static void cpu_ioreq_pio(ioreq_t *req)
 
 static void cpu_ioreq_move(ioreq_t *req)
 {
-    int i, sign;
-
-    sign = req->df ? -1 : 1;
+    int i;
 
     if (!req->data_is_ptr) {
         if (req->dir == IOREQ_READ) {
             for (i = 0; i < req->count; i++) {
-                cpu_physical_memory_read(
-                        req->addr + (sign * i * (int64_t)req->size),
-                        (uint8_t *) &req->data, req->size);
+                read_phys_req_item(req->addr, req, i, &req->data);
             }
         } else if (req->dir == IOREQ_WRITE) {
             for (i = 0; i < req->count; i++) {
-                cpu_physical_memory_write(
-                        req->addr + (sign * i * (int64_t)req->size),
-                        (uint8_t *) &req->data, req->size);
+                write_phys_req_item(req->addr, req, i, &req->data);
             }
         }
     } else {
@@ -743,21 +767,13 @@ static void cpu_ioreq_move(ioreq_t *req)
 
         if (req->dir == IOREQ_READ) {
             for (i = 0; i < req->count; i++) {
-                cpu_physical_memory_read(
-                        req->addr + (sign * i * (int64_t)req->size),
-                        (uint8_t*) &tmp, req->size);
-                cpu_physical_memory_write(
-                        req->data + (sign * i * (int64_t)req->size),
-                        (uint8_t*) &tmp, req->size);
+                read_phys_req_item(req->addr, req, i, &tmp);
+                write_phys_req_item(req->data, req, i, &tmp);
             }
         } else if (req->dir == IOREQ_WRITE) {
             for (i = 0; i < req->count; i++) {
-                cpu_physical_memory_read(
-                        req->data + (sign * i * (int64_t)req->size),
-                        (uint8_t*) &tmp, req->size);
-                cpu_physical_memory_write(
-                        req->addr + (sign * i * (int64_t)req->size),
-                        (uint8_t*) &tmp, req->size);
+                read_phys_req_item(req->data, req, i, &tmp);
+                write_phys_req_item(req->addr, req, i, &tmp);
             }
         }
     }