Add "fast page" to KERNEL_OFFSET. This is always present in page
tables and only requires changing the page table entry to map. This
requires no interrupts since it should only be for very operations
like memcpy.
I used to map all temporary mappings to vaddr 0, but this is much
better. C++ standard always says that nullptr access is undefined
and this gets rid of it.
Fixed some bugs I found along the way
Before reserving address space in SYS_EXEC verify that ELF address
space is actually loadable. For example when trying to execute the
kernel binary in userspace, binarys address space would overlap with
current kernel address space. Now kernel won't crash anymore and
will just send SIGKILL to the process calling exec*().
We only clone mapped pages that have been marked as writeble.
Read/execute only pages will be exactly as in the file itself and
can be demand paged also :D
We now load ELF files to VirtualRanges instead of using kmalloc.
We have only a fixed 1 MiB kmalloc for big allocations and this
allows loading files even when they don't fit in there.
This caused me to rewrite the whole ELF loading process since the
loaded ELF is not in memory mapped by every process.
Virtual ranges allow you to zero out the memory and to copy into
them from arbitary byte buffers.
Bananymous
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