fix UB that cause warning

common/iovector.h

@@ -34,6 +34,7 @@ limitations under the License.
 #include <cstring>
 #include <new>
 #include <memory>
+#include <array>
 #include <sys/uio.h>
 
 #include <photon/common/callback.h>
@@ -308,34 +309,34 @@ class iovector
  struct iovec* begin()
  {
  do_assert();
- return iovs + iov_begin;
+ return iovs_ptr() + iov_begin;
  }
  const struct iovec* begin() const
  {
  do_assert();
- return iovs + iov_begin;
+ return iovs_ptr() + iov_begin;
  }
  struct iovec* end()
  {
  do_assert();
- return iovs + iov_end;
+ return iovs_ptr() + iov_end;
  }
  const struct iovec* end() const
  {
  do_assert();
- return iovs + iov_end;
+ return iovs_ptr() + iov_end;
  }
  struct iovec& operator[] (int64_t i)
  {
  do_assert();
  assert(iov_begin + i < iov_end);
- return iovs[iov_begin + i];
+ return iovs_ptr()[iov_begin + i];
  }
  const struct iovec& operator[] (int64_t i) const
  {
  do_assert();
  assert(iov_begin + i < iov_end);
- return iovs[iov_begin + i];
+ return iovs_ptr()[iov_begin + i];
  }
 
  // push some stuff to the front, and
@@ -344,7 +345,7 @@ class iovector
  {
  do_assert();
  IF_ASSERT_RETURN(iov_begin > 0, 0);
- iovs[--iov_begin] = iov;
+ iovs_ptr()[--iov_begin] = iov;
  return iov.iov_len;
  }
  size_t push_front(void* buf, size_t size)
@@ -369,7 +370,7 @@ class iovector
  {
  do_assert();
  IF_ASSERT_RETURN(iov_end < capacity, 0);
- iovs[iov_end++] = iov;
+ iovs_ptr()[iov_end++] = iov;
  return iov.iov_len;
  }
  size_t push_back(void* buf, size_t size)
@@ -393,13 +394,13 @@ class iovector
  {
  do_assert();
  IF_ASSERT_RETURN(!empty(), 0);
- return iovs[iov_begin++].iov_len;
+ return iovs_ptr()[iov_begin++].iov_len;
  }
  size_t pop_back()
  {
  do_assert();
  IF_ASSERT_RETURN(!empty(), 0);
- return iovs[--iov_end].iov_len;
+ return iovs_ptr()[--iov_end].iov_len;
  }
 
  void clear() // doesn't dispose()
@@ -772,7 +773,7 @@ class iovector
  clear_dispose();
  iov_end = end;
 
- memcpy(begin(), rhs.begin(), iovcnt() * sizeof(iovs[0]));
+ memcpy(begin(), rhs.begin(), iovcnt() * sizeof(iovs_ptr()[0]));
  allocator()->copy(rhs.allocator(), rhs.nbases);
  nbases = rhs.nbases;
  rhs.nbases = 0;
@@ -791,7 +792,7 @@ class iovector
  }
 
  void update(iovector_view va) {
- iov_begin = va.iov - iovs;
+ iov_begin = va.iov - iovs_ptr();
  iov_end = iov_begin + va.iovcnt;
  }
 
@@ -827,7 +828,7 @@ class iovector
  uint16_t capacity; // total capacity
  uint16_t iov_begin, iov_end; // [iov_begin, iov_end)
  uint16_t nbases; // # of allocated pointers
- struct iovec iovs[0];
+ // struct iovec iovs[];
 
  friend iovector* new_iovector(uint16_t capacity, uint16_t preserve);
  friend void delete_iovector(iovector* ptr);
@@ -841,7 +842,7 @@ class iovector
 
  inline __attribute__((always_inline))
  struct iovec* iovs_ptr() const {
- return const_cast<struct iovec*>(iovs);
+ return reinterpret_cast<struct iovec*>(const_cast<iovector*>(this + 1));
  }
 
  // not allowed to freely construct / destruct
@@ -861,7 +862,7 @@ class iovector
 
  struct IOVAllocation_ : public IOAlloc
  {
- void* bases[0];
+ void* bases[];
  void* do_allocate(int size, uint16_t& nbases, uint16_t capacity)
  {
  return do_allocate(size, size, nbases, capacity);
@@ -898,7 +899,7 @@ class iovector
 
  IOVAllocation_* allocator() const
  { // this makes an assumption of the memory layout as `IOVectorEntity`
- auto addr = (char*)this + sizeof(*this) +sizeof(iovs[0]) * capacity;
+ auto addr = (char*)this + sizeof(*this) +sizeof(iovs_ptr()[0]) * capacity;
  return (IOVAllocation_*)addr;
  }
  void dispose()