linux-user: added support for pwritev() system call.

This system call performs the same task as the writev() system call,
with the exception of having the fourth argument, offset, which
specifes the file offset at which the input operation is to be performed.
Because of this, the pwritev() implementation is based on the writev()
implementation in linux-user mode.

But, since pwritev() is implemented in the kernel as a 5-argument syscall,
5 arguments are needed to be handled as input and passed to the host
syscall.

The pos_l and pos_h argument of the safe_pwritev() are of type unsigned
long, which can be of different sizes on different platforms. The input
arguments are converted to the appropriate host size when passed to
safe_pwritev().
Signed-off-by: NDejan Jovicevic <dejan.jovicevic@rt-rk.com>
Signed-off-by: NRiku Voipio <riku.voipio@linaro.org>

linux-user/syscall.c

@@ -920,6 +920,8 @@ safe_syscall3(ssize_t, readv, int, fd, const struct iovec *, iov, int, iovcnt)
 safe_syscall3(ssize_t, writev, int, fd, const struct iovec *, iov, int, iovcnt)
 safe_syscall5(ssize_t, preadv, int, fd, const struct iovec *, iov, int, iovcnt,
               unsigned long, pos_l, unsigned long, pos_h)
+safe_syscall5(ssize_t, pwritev, int, fd, const struct iovec *, iov, int, iovcnt,
+              unsigned long, pos_l, unsigned long, pos_h)
 safe_syscall3(int, connect, int, fd, const struct sockaddr *, addr,
               socklen_t, addrlen)
 safe_syscall6(ssize_t, sendto, int, fd, const void *, buf, size_t, len,
@@ -10073,6 +10075,19 @@ abi_long do_syscall(void *cpu_env, int num, abi_long arg1,
            }
         }
         break;
+#endif
+#if defined(TARGET_NR_pwritev)
+    case TARGET_NR_pwritev:
+        {
+            struct iovec *vec = lock_iovec(VERIFY_READ, arg2, arg3, 1);
+            if (vec != NULL) {
+                ret = get_errno(safe_pwritev(arg1, vec, arg3, arg4, arg5));
+                unlock_iovec(vec, arg2, arg3, 0);
+            } else {
+                ret = -host_to_target_errno(errno);
+           }
+        }
+        break;
 #endif
     case TARGET_NR_getsid:
         ret = get_errno(getsid(arg1));