Implement user mode tasks with syscall support #275
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Signed-off-by: Pawel Wieczorkiewicz <[email protected]>
This uses a very simple (and just good enough for now) origin detection mechanism. Kernel -> User or User -> Kernel tranistion is decided based on CS selector value on the stack (CPL bits checks). When privilege tranistion is detected a CR3 pagetable switch occurs as well as swapgs for percpu segment (userland has it set to NULL). User pagetables need a kernel mapping of CR3 register and percpu page to be able to switch to it on interrupt/exception. Signed-off-by: Pawel Wieczorkiewicz <[email protected]>
Signed-off-by: Pawel Wieczorkiewicz <[email protected]>
Signed-off-by: Pawel Wieczorkiewicz <[email protected]>
This routine preserves all kernel registers upon invocation. It receives user stack pointer via 3rd parameter instead of via a percpu location. Signed-off-by: Pawel Wieczorkiewicz <[email protected]>
Allocate user task stack and keep a reference in the task_t structure. Add enter_usermode() to the user pagetables kernel mappings. Signed-off-by: Pawel Wieczorkiewicz <[email protected]>
The exit system call has index 0. It is used by usermode_stub() to exit back to kernel, when user task is finished. Signed-off-by: Pawel Wieczorkiewicz <[email protected]>
…its) Signed-off-by: Pawel Wieczorkiewicz <[email protected]>
Exceptions occuring in usermode terminate a user task, but are not fatal for the kernel. Signed-off-by: Pawel Wieczorkiewicz <[email protected]>
Signed-off-by: Pawel Wieczorkiewicz <[email protected]>
The printf() system call accepts only 4 parameters: format string and for parameters for it. There is no variadic parameters support and there is also no checks for the sanity of the format string vs parameters list. Use with care. Signed-off-by: Pawel Wieczorkiewicz <[email protected]>
Signed-off-by: Pawel Wieczorkiewicz <[email protected]>
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Implements #55