Mapping virtual memory to virtual memory

Question

I am supplied with a struct that lies somewhere in the memory. Is it possible in WinAPI/POSIX to create a memory mapping that would alias the struct to a different part of the memory range so that identical bytes could be accessed from both locations? I cannot control the location of the original struct, but the new one can be stored anywhere.

I think, at least in WinAPI, I could create a temporary file and store the pages that contain the struct there, and then I could (hopefully) replace the original pages with new ones that point to the file, then map the file to a new section in the memory. However, I am worried about the performance of accessing the memory. Is there something better?

Answer 1

In Linux you can use memfd_create(2) to allocate memory which you can access through a file descriptor. You'd then write(2) the original data to that in-memory file and map it over the original location with mmap(2) using MAP_FIXED flag, and then to another location with a non-fixed mmap(2) . Be aware that mapping must be a multiple of the underlying page size (4k in regular address space, or hugepage size if the memfd was allocated from hugepages).