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https://github.com/RGBCube/serenity
synced 2025-05-30 17:58:11 +00:00
Implement fork()!
This is quite cool! The syscall entry point plumbs the register dump down to sys$fork(), which uses it to set up the child process's TSS in order to resume execution right after the int 0x80 fork() call. :^) This works pretty well, although there is some problem with the kernel alias mappings used to clone the parent process's regions. If I disable the MM::release_page_directory() code, there's no problem. Probably there's a premature freeing of a physical page somehow.
This commit is contained in:
Andreas Kling
parent
10b666f69a
commit
8accc92c3c
16 changed files with 228 additions and 78 deletions
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@ -105,30 +105,6 @@ void Process::initialize()
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loadTaskRegister(s_kernelProcess->selector());
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}
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void Process::allocateLDT()
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{
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ASSERT(!m_tss.ldt);
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static const WORD numLDTEntries = 4;
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m_ldt_selector = gdt_alloc_entry();
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m_ldtEntries = new Descriptor[numLDTEntries];
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#if 0
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kprintf("new ldt selector = %x\n", m_ldt_selector);
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kprintf("new ldt table at = %p\n", m_ldtEntries);
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kprintf("new ldt table size = %u\n", (numLDTEntries * 8) - 1);
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#endif
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Descriptor& ldt = getGDTEntry(m_ldt_selector);
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ldt.setBase(m_ldtEntries);
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ldt.setLimit(numLDTEntries * 8 - 1);
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ldt.dpl = 0;
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ldt.segment_present = 1;
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ldt.granularity = 0;
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ldt.zero = 0;
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ldt.operation_size = 1;
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ldt.descriptor_type = 0;
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ldt.type = Descriptor::LDT;
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m_tss.ldt = m_ldt_selector;
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}
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template<typename Callback>
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static void forEachProcess(Callback callback)
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{
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@ -235,6 +211,77 @@ int Process::sys$gethostname(char* buffer, size_t size)
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return 0;
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}
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Process* Process::fork(RegisterDump& regs)
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{
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auto* child = new Process(String(m_name), m_uid, m_gid, m_pid, m_ring, m_cwd.copyRef(), m_executable.copyRef(), m_tty, this);
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#ifdef FORK_DEBUG
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dbgprintf("fork: child=%p\n", child);
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#endif
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#if 0
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// FIXME: An honest fork() would copy these. Needs a Vector copy ctor.
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child->m_arguments = m_arguments;
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child->m_initialEnvironment = m_initialEnvironment;
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#endif
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for (auto& region : m_regions) {
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#ifdef FORK_DEBUG
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dbgprintf("fork: cloning Region{%p}\n", region.ptr());
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#endif
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auto cloned_region = region->clone();
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// FIXME: Move subregions into Region?
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for (auto& subregion : m_subregions) {
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if (subregion->region.ptr() != region.ptr())
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continue;
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#ifdef FORK_DEBUG
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dbgprintf("fork: cloning Subregion{%p}\n", subregion.ptr());
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#endif
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auto cloned_subregion = make<Subregion>(*cloned_region, subregion->offset, subregion->size, subregion->linearAddress, String(subregion->name));
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child->m_subregions.append(move(cloned_subregion));
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MM.mapSubregion(*child, *child->m_subregions.last());
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}
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child->m_regions.append(move(cloned_region));
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MM.mapRegion(*child, *child->m_regions.last());
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}
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child->m_tss.eax = 0; // fork() returns 0 in the child :^)
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child->m_tss.ebx = regs.ebx;
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child->m_tss.ecx = regs.ecx;
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child->m_tss.edx = regs.edx;
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child->m_tss.ebp = regs.ebp;
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child->m_tss.esp = regs.esp_if_crossRing;
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child->m_tss.esi = regs.esi;
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child->m_tss.edi = regs.edi;
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child->m_tss.eflags = regs.eflags;
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child->m_tss.eip = regs.eip;
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child->m_tss.cs = regs.cs;
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child->m_tss.ds = regs.ds;
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child->m_tss.es = regs.es;
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child->m_tss.fs = regs.fs;
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child->m_tss.gs = regs.gs;
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child->m_tss.ss = regs.ss_if_crossRing;
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#ifdef FORK_DEBUG
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dbgprintf("fork: child will begin executing at %w:%x with stack %w:%x\n", child->m_tss.cs, child->m_tss.eip, child->m_tss.ss, child->m_tss.esp);
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#endif
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ProcFileSystem::the().addProcess(*child);
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s_processes->prepend(child);
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system.nprocess++;
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#ifdef TASK_DEBUG
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kprintf("Process %u (%s) forked from %u @ %p\n", child->pid(), child->name().characters(), m_pid, child->m_tss.eip);
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#endif
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return child;
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}
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pid_t Process::sys$fork(RegisterDump& regs)
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{
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auto* child = fork(regs);
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ASSERT(child);
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return child->pid();
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}
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int Process::sys$spawn(const char* path, const char** args)
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{
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if (args) {
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@ -413,9 +460,9 @@ Process* Process::createKernelProcess(void (*e)(), String&& name)
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return process;
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}
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Process::Process(String&& name, uid_t uid, gid_t gid, pid_t parentPID, RingLevel ring, RetainPtr<VirtualFileSystem::Node>&& cwd, RetainPtr<VirtualFileSystem::Node>&& executable, TTY* tty)
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Process::Process(String&& name, uid_t uid, gid_t gid, pid_t parentPID, RingLevel ring, RetainPtr<VirtualFileSystem::Node>&& cwd, RetainPtr<VirtualFileSystem::Node>&& executable, TTY* tty, Process* fork_parent)
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: m_name(move(name))
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, m_pid(next_pid++)
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, m_pid(next_pid++) // FIXME: RACE: This variable looks racy!
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, m_uid(uid)
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, m_gid(gid)
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, m_state(Runnable)
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@ -425,57 +472,71 @@ Process::Process(String&& name, uid_t uid, gid_t gid, pid_t parentPID, RingLevel
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, m_tty(tty)
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, m_parentPID(parentPID)
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{
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{
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if (fork_parent) {
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m_sid = fork_parent->m_sid;
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m_pgid = fork_parent->m_pgid;
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} else {
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// FIXME: Use a ProcessHandle? Presumably we're executing *IN* the parent right now though..
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InterruptDisabler disabler;
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if (auto* parent = Process::fromPID(m_parentPID)) {
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m_sid = parent->m_sid;
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m_pgid = parent->m_pgid;
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}
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}
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m_page_directory = (PageDirectory*)kmalloc_page_aligned(sizeof(PageDirectory));
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MM.populate_page_directory(*this);
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m_file_descriptors.resize(m_max_open_file_descriptors);
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if (tty) {
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m_file_descriptors[0] = tty->open(O_RDONLY);
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m_file_descriptors[1] = tty->open(O_WRONLY);
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m_file_descriptors[2] = tty->open(O_WRONLY);
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}
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m_nextRegion = LinearAddress(0x10000000);
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memset(&m_tss, 0, sizeof(m_tss));
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if (isRing3()) {
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memset(&m_ldtEntries, 0, sizeof(m_ldtEntries));
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allocateLDT();
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}
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// Only IF is set when a process boots.
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m_tss.eflags = 0x0202;
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word cs, ds, ss;
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if (isRing0()) {
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cs = 0x08;
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ds = 0x10;
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ss = 0x10;
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if (fork_parent) {
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m_file_descriptors.resize(fork_parent->m_file_descriptors.size());
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for (size_t i = 0; i < fork_parent->m_file_descriptors.size(); ++i) {
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if (!fork_parent->m_file_descriptors[i])
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continue;
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#ifdef FORK_DEBUG
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dbgprintf("fork: cloning fd %u... (%p) istty? %um\n", i, fork_parent->m_file_descriptors[i].ptr(), fork_parent->m_file_descriptors[i]->isTTY());
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#endif
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m_file_descriptors[i] = fork_parent->m_file_descriptors[i]->clone();
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}
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} else {
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cs = 0x1b;
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ds = 0x23;
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ss = 0x23;
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m_file_descriptors.resize(m_max_open_file_descriptors);
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if (tty) {
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m_file_descriptors[0] = tty->open(O_RDONLY);
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m_file_descriptors[1] = tty->open(O_WRONLY);
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m_file_descriptors[2] = tty->open(O_WRONLY);
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}
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}
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m_tss.ds = ds;
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m_tss.es = ds;
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m_tss.fs = ds;
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m_tss.gs = ds;
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m_tss.ss = ss;
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m_tss.cs = cs;
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if (fork_parent)
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m_nextRegion = fork_parent->m_nextRegion;
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else
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m_nextRegion = LinearAddress(0x10000000);
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if (fork_parent) {
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memcpy(&m_tss, &fork_parent->m_tss, sizeof(m_tss));
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} else {
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memset(&m_tss, 0, sizeof(m_tss));
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// Only IF is set when a process boots.
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m_tss.eflags = 0x0202;
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word cs, ds, ss;
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if (isRing0()) {
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cs = 0x08;
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ds = 0x10;
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ss = 0x10;
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} else {
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cs = 0x1b;
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ds = 0x23;
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ss = 0x23;
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}
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m_tss.ds = ds;
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m_tss.es = ds;
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m_tss.fs = ds;
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m_tss.gs = ds;
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m_tss.ss = ss;
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m_tss.cs = cs;
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}
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m_tss.cr3 = (dword)m_page_directory;
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@ -486,10 +547,14 @@ Process::Process(String&& name, uid_t uid, gid_t gid, pid_t parentPID, RingLevel
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m_stackTop0 = (stackBottom + defaultStackSize) & 0xffffff8;
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m_tss.esp = m_stackTop0;
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} else {
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auto* region = allocateRegion(defaultStackSize, "stack");
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ASSERT(region);
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m_stackTop3 = region->linearAddress.offset(defaultStackSize).get() & 0xfffffff8;
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m_tss.esp = m_stackTop3;
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if (fork_parent) {
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m_stackTop3 = fork_parent->m_stackTop3;
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} else {
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auto* region = allocateRegion(defaultStackSize, "stack");
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ASSERT(region);
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m_stackTop3 = region->linearAddress.offset(defaultStackSize).get() & 0xfffffff8;
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m_tss.esp = m_stackTop3;
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}
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}
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if (isRing3()) {
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@ -511,12 +576,6 @@ Process::~Process()
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ProcFileSystem::the().removeProcess(*this);
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system.nprocess--;
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if (isRing3()) {
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delete [] m_ldtEntries;
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m_ldtEntries = nullptr;
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gdt_free_entry(m_ldt_selector);
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}
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gdt_free_entry(selector());
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if (m_kernelStack) {
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