Problems loading Conway v0.1-pre1 release

[m44rtn]

Vireo build: 3658 (v0.1-pre1, release)

Describe the bug
Vireo may have trouble loading conway.elf on systems with more than 79 MB of memory. The system may kernel panic (non present page fault) or halt completely due to a triple fault.

[m44rtn]

#21

[m44rtn]

latest commit still has this issue (build 3850).

[m44rtn]

The problem is caused by shadow_t (paging.c) which takes up around 61 KiB when the system has 80 megabytes of ram or more. shadow_t Is currently stored in memory using kmalloc. Kmalloc has 65 KiB of space at its disposal to allocate, and apparently the kernel needs a little over 4 KiB to function correctly in its current state.

When the ISO9660 driver starts reversing file paths, the system does not have any kmalloc space left and it returns NULL. Since reverse_path does not check for NULL pointers, this caused the problem of an underflow at some point in the function and the kernel tries to write to memory address 0xFFFFFFFF (4 GiB - 1), which is not available since the available memory is only 80 MB.

The solution is to either move shadow_t to a better location (preferred), or grow kmalloc allocation space size based on how much memory is available in a given system.