Kernel: Add x86_64 support for fork()

Kernel/Arch/x86/common/Processor.cpp

@@ -39,6 +39,7 @@ Atomic<u32> Processor::s_idle_cpu_mask { 0 };
 
 extern "C" void thread_context_first_enter(void);
 extern "C" void exit_kernel_thread(void);
+extern "C" void do_assume_context(Thread* thread, u32 flags);
 
 // The compiler can't see the calls to these functions inside assembly.
 // Declare them, to avoid dead code warnings.
@@ -1233,4 +1234,20 @@ extern "C" FlatPtr do_init_context(Thread* thread, u32 flags)
 #endif
     return Processor::current().init_context(*thread, true);
 }
+
+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);
+
+    do_assume_context(&thread, flags);
+
+    VERIFY_NOT_REACHED();
+}
+
 }

Kernel/Arch/x86/i386/Processor.cpp

@@ -17,7 +17,6 @@ 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
@@ -236,21 +235,6 @@ void Processor::switch_context(Thread*& from_thread, 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);
-
-    do_assume_context(&thread, flags);
-
-    VERIFY_NOT_REACHED();
-}
-
 UNMAP_AFTER_INIT void Processor::initialize_context_switching(Thread& initial_thread)
 {
     VERIFY(initial_thread.process().is_kernel_process());

Kernel/Arch/x86/x86_64/Processor.cpp

@@ -16,7 +16,6 @@
 namespace Kernel {
 
 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
@@ -50,6 +49,8 @@ asm(
 "    movq %rax, %rsp \n" // move stack pointer to what Processor::init_context set up for us
 "    movq %r12, %rdi \n" // to_thread
 "    movq %r12, %rsi \n" // from_thread
+"    pushq %r12 \n" // to_thread (for thread_context_first_enter)
+"    pushq %r12 \n" // from_thread (for thread_context_first_enter)
 "    movabs $thread_context_first_enter, %r12 \n" // should be same as regs.rip
 "    pushq %r12 \n"
 "    jmp enter_thread_context \n"
@@ -238,22 +239,6 @@ void Processor::switch_context(Thread*& from_thread, 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());

Kernel/Syscalls/fork.cpp

@@ -66,8 +66,29 @@ KResultOr<FlatPtr> Process::sys$fork(RegisterState& regs)
     dbgln_if(FORK_DEBUG, "fork: child will begin executing at {:04x}:{:08x} with stack {:04x}:{:08x}, kstack {:04x}:{:08x}",
         child_regs.cs, child_regs.eip, child_regs.ss, child_regs.esp, child_regs.ss0, child_regs.esp0);
 #else
-    (void)regs;
+    auto& child_regs = child_first_thread->m_regs;
-    PANIC("Process::sys$fork() not implemented.");
+    child_regs.rax = 0; // fork() returns 0 in the child :^)
+    child_regs.rbx = regs.rbx;
+    child_regs.rcx = regs.rcx;
+    child_regs.rdx = regs.rdx;
+    child_regs.rbp = regs.rbp;
+    child_regs.rsp = regs.userspace_rsp;
+    child_regs.rsi = regs.rsi;
+    child_regs.rdi = regs.rdi;
+    child_regs.r8 = regs.r8;
+    child_regs.r9 = regs.r9;
+    child_regs.r10 = regs.r10;
+    child_regs.r11 = regs.r11;
+    child_regs.r12 = regs.r12;
+    child_regs.r13 = regs.r13;
+    child_regs.r14 = regs.r14;
+    child_regs.r15 = regs.r15;
+    child_regs.rflags = regs.rflags;
+    child_regs.rip = regs.rip;
+    child_regs.cs = regs.cs;
+
+    dbgln_if(FORK_DEBUG, "fork: child will begin executing at {:04x}:{:16x} with stack {:08x}, kstack {:08x}",
+        child_regs.cs, child_regs.rip, child_regs.rsp, child_regs.rsp0);
 #endif
 
     {