While I was updating syscalls to stop passing null-terminated strings,
I added some helpful struct types:
- StringArgument { const char*; size_t; }
- ImmutableBuffer<Data, Size> { const Data*; Size; }
- MutableBuffer<Data, Size> { Data*; Size; }
The Process class has some convenience functions for validating and
optionally extracting the contents from these structs:
- get_syscall_path_argument(StringArgument)
- validate_and_copy_string_from_user(StringArgument)
- validate(ImmutableBuffer)
- validate(MutableBuffer)
There's still so much code around this and I'm wondering if we should
generate most of it instead. Possible nice little project.
This code never worked, as was never used for anything. We can build
a much better SHM implementation on top of TmpFS or similar when we
get to the point when we need one.
It's now possible to get purgeable memory by using mmap(MAP_PURGEABLE).
Purgeable memory has a "volatile" flag that can be set using madvise():
- madvise(..., MADV_SET_VOLATILE)
- madvise(..., MADV_SET_NONVOLATILE)
When in the "volatile" state, the kernel may take away the underlying
physical memory pages at any time, without notifying the owner.
This gives you a guilt discount when caching very large things. :^)
Setting a purgeable region to non-volatile will return whether or not
the memory has been taken away by the kernel while being volatile.
Basically, if madvise(..., MADV_SET_NONVOLATILE) returns 1, that means
the memory was purged while volatile, and whatever was in that piece
of memory needs to be reconstructed before use.
This patch adds the mprotect() syscall to allow changing the protection
flags for memory regions. We don't do any region splitting/merging yet,
so this only works on whole mmap() regions.
Added a "crash -r" flag to verify that we crash when you attempt to
write to read-only memory. :^)
