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/*
* Copyright (c) 2018-2021, Andreas Kling <kling@serenityos.org>
*
* SPDX-License-Identifier: BSD-2-Clause
*/
#include <AK/StdLibExtras.h>
#include <Kernel/Arch/x86/Processor.h>
#include <Kernel/Arch/x86/TrapFrame.h>
#include <Kernel/Panic.h>
#include <Kernel/Process.h>
#include <Kernel/Random.h>
#include <Kernel/Sections.h>
#include <Kernel/Thread.h>
namespace Kernel {
#define ENTER_THREAD_CONTEXT_ARGS_SIZE (2 * 4) // to_thread, from_thread
extern "C" void thread_context_first_enter(void);
extern "C" void do_assume_context(Thread* thread, u32 flags);
extern "C" void exit_kernel_thread(void);
// clang-format off
asm(
// enter_thread_context returns to here first time a thread is executing
".globl thread_context_first_enter \n"
"thread_context_first_enter: \n"
// switch_context will have pushed from_thread and to_thread to our new
// stack prior to thread_context_first_enter() being called, and the
// pointer to TrapFrame was the top of the stack before that
" movl 8(%esp), %ebx \n" // save pointer to TrapFrame
" cld \n"
" call context_first_init \n"
" addl $" __STRINGIFY(ENTER_THREAD_CONTEXT_ARGS_SIZE) ", %esp \n"
" movl %ebx, 0(%esp) \n" // push pointer to TrapFrame
" jmp common_trap_exit \n"
);
// clang-format on
#if ARCH(I386)
// clang-format off
asm(
".global do_assume_context \n"
"do_assume_context: \n"
" movl 4(%esp), %ebx \n"
" movl 8(%esp), %esi \n"
// We're going to call Processor::init_context, so just make sure
// we have enough stack space so we don't stomp over it
" subl $(" __STRINGIFY(4 + REGISTER_STATE_SIZE + TRAP_FRAME_SIZE + 4) "), %esp \n"
" pushl %esi \n"
" pushl %ebx \n"
" cld \n"
" call do_init_context \n"
" addl $8, %esp \n"
" movl %eax, %esp \n" // move stack pointer to what Processor::init_context set up for us
" pushl %ebx \n" // push to_thread
" pushl %ebx \n" // push from_thread
" pushl $thread_context_first_enter \n" // should be same as tss.eip
" jmp enter_thread_context \n"
);
// clang-format on
#endif
String Processor::platform_string() const
{
// FIXME: other platforms
return "x86_64";
}
u32 Processor::init_context(Thread& thread, bool leave_crit)
{
VERIFY(is_kernel_mode());
VERIFY(g_scheduler_lock.is_locked());
if (leave_crit) {
// Leave the critical section we set up in in Process::exec,
// but because we still have the scheduler lock we should end up with 1
m_in_critical--; // leave it without triggering anything or restoring flags
VERIFY(in_critical() == 1);
}
u32 kernel_stack_top = thread.kernel_stack_top();
// Add a random offset between 0-256 (16-byte aligned)
kernel_stack_top -= round_up_to_power_of_two(get_fast_random<u8>(), 16);
u32 stack_top = kernel_stack_top;
// TODO: handle NT?
VERIFY((cpu_flags() & 0x24000) == 0); // Assume !(NT | VM)
auto& tss = thread.tss();
bool return_to_user = (tss.cs & 3) != 0;
// make room for an interrupt frame
if (!return_to_user) {
// userspace_esp and userspace_ss are not popped off by iret
// unless we're switching back to user mode
stack_top -= sizeof(RegisterState) - 2 * sizeof(u32);
// For kernel threads we'll push the thread function argument
// which should be in tss.esp and exit_kernel_thread as return
// address.
stack_top -= 2 * sizeof(u32);
*reinterpret_cast<u32*>(kernel_stack_top - 2 * sizeof(u32)) = tss.esp;
*reinterpret_cast<u32*>(kernel_stack_top - 3 * sizeof(u32)) = FlatPtr(&exit_kernel_thread);
} else {
stack_top -= sizeof(RegisterState);
}
// we want to end up 16-byte aligned, %esp + 4 should be aligned
stack_top -= sizeof(u32);
*reinterpret_cast<u32*>(kernel_stack_top - sizeof(u32)) = 0;
// set up the stack so that after returning from thread_context_first_enter()
// we will end up either in kernel mode or user mode, depending on how the thread is set up
// However, the first step is to always start in kernel mode with thread_context_first_enter
RegisterState& iretframe = *reinterpret_cast<RegisterState*>(stack_top);
// FIXME: copy state to be recovered through TSS
TODO();
// make space for a trap frame
stack_top -= sizeof(TrapFrame);
TrapFrame& trap = *reinterpret_cast<TrapFrame*>(stack_top);
trap.regs = &iretframe;
trap.prev_irq_level = 0;
trap.next_trap = nullptr;
stack_top -= sizeof(u32); // pointer to TrapFrame
*reinterpret_cast<u32*>(stack_top) = stack_top + 4;
if constexpr (CONTEXT_SWITCH_DEBUG) {
if (return_to_user) {
dbgln("init_context {} ({}) set up to execute at eip={}:{}, esp={}, stack_top={}, user_top={}:{}",
thread,
VirtualAddress(&thread),
iretframe.cs, tss.eip,
VirtualAddress(tss.esp),
VirtualAddress(stack_top),
iretframe.userspace_ss,
iretframe.userspace_esp);
} else {
dbgln("init_context {} ({}) set up to execute at eip={}:{}, esp={}, stack_top={}",
thread,
VirtualAddress(&thread),
iretframe.cs, tss.eip,
VirtualAddress(tss.esp),
VirtualAddress(stack_top));
}
}
// make switch_context() always first return to thread_context_first_enter()
// in kernel mode, so set up these values so that we end up popping iretframe
// off the stack right after the context switch completed, at which point
// control is transferred to what iretframe is pointing to.
tss.eip = FlatPtr(&thread_context_first_enter);
tss.esp0 = kernel_stack_top;
tss.esp = stack_top;
tss.cs = GDT_SELECTOR_CODE0;
tss.ds = GDT_SELECTOR_DATA0;
tss.es = GDT_SELECTOR_DATA0;
tss.gs = GDT_SELECTOR_DATA0;
tss.ss = GDT_SELECTOR_DATA0;
tss.fs = GDT_SELECTOR_PROC;
return stack_top;
}
void Processor::switch_context(Thread*& from_thread, Thread*& to_thread)
{
VERIFY(!in_irq());
VERIFY(m_in_critical == 1);
VERIFY(is_kernel_mode());
dbgln_if(CONTEXT_SWITCH_DEBUG, "switch_context --> switching out of: {} {}", VirtualAddress(from_thread), *from_thread);
from_thread->save_critical(m_in_critical);
PANIC("Context switching not implemented.");
dbgln_if(CONTEXT_SWITCH_DEBUG, "switch_context <-- from {} {} to {} {}", VirtualAddress(from_thread), *from_thread, VirtualAddress(to_thread), *to_thread);
Processor::current().restore_in_critical(to_thread->saved_critical());
}
void Processor::assume_context(Thread& thread, FlatPtr flags)
{
dbgln_if(CONTEXT_SWITCH_DEBUG, "Assume context for thread {} {}", VirtualAddress(&thread), thread);
VERIFY_INTERRUPTS_DISABLED();
Scheduler::prepare_after_exec();
// in_critical() should be 2 here. The critical section in Process::exec
// and then the scheduler lock
VERIFY(Processor::current().in_critical() == 2);
(void)flags;
TODO();
VERIFY_NOT_REACHED();
}
UNMAP_AFTER_INIT void Processor::initialize_context_switching(Thread& initial_thread)
{
VERIFY(initial_thread.process().is_kernel_process());
auto& tss = initial_thread.tss();
m_tss = tss;
m_tss.esp0 = tss.esp0;
m_tss.ss0 = GDT_SELECTOR_DATA0;
// user mode needs to be able to switch to kernel mode:
m_tss.cs = m_tss.ds = m_tss.es = m_tss.gs = m_tss.ss = GDT_SELECTOR_CODE0 | 3;
m_tss.fs = GDT_SELECTOR_PROC | 3;
m_scheduler_initialized = true;
// FIXME: Context switching (see i386 impl)
VERIFY_NOT_REACHED();
}
}
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