CreateUninitializedVector was performing the following actions:
1. call StartVector.
2. call make_space, and set buf to point to the reserved space.
3. call EndVector.
The problem is that a call to EndVector can ultimately call make_space, which
if the buffer is full, will cause a reallocation, invalidating the value stored
in buf. So setting buf needs to be delayed until after EndVector.
The following code, when run under valgrind shows a write to free'd memory before
the change, but no such error after:
int main()
{
flatbuffers::FlatBufferBuilder fbb(128);
char *buf = nullptr;
fbb.CreateUninitializedVector(128, &buf);
*buf = 0;
}
uint8_t **buf) {
NotNested();
StartVector(len, elemsize);
- *buf = buf_.make_space(len * elemsize);
- return EndVector(len);
+ buf_.make_space(len * elemsize);
+ auto vec_start = GetSize();
+ auto vec_end = EndVector(len);
+ *buf = buf_.data_at(vec_start);
+ return vec_end;
}
/// @brief Specialized version of `CreateVector` for non-copying use cases.