initial check-in, version 0.5.0

src/thread/pthread_create.c

@@ -0,0 +1,189 @@
+#include "pthread_impl.h"
+
+#define pthread_self __pthread_self
+
+static void docancel(struct pthread *self)
+{
+	struct __ptcb cb = { .__next = self->cancelbuf };
+	__pthread_unwind_next(&cb);
+}
+
+static void cancel_handler(int sig, siginfo_t *si, void *ctx)
+{
+	struct pthread *self = pthread_self();
+	self->cancel = 1;
+	if (self->canceldisable || (!self->cancelasync && !self->cancelpoint))
+		return;
+	docancel(self);
+}
+
+/* "rsyscall" is a mechanism by which a thread can synchronously force all
+ * other threads to perform an arbitrary syscall. It is necessary to work
+ * around the non-conformant implementation of setuid() et al on Linux,
+ * which affect only the calling thread and not the whole process. This
+ * implementation performs some tricks with signal delivery to work around
+ * the fact that it does not keep any list of threads in userspace. */
+
+static struct {
+	volatile int lock, hold, blocks, cnt;
+	unsigned long arg[6];
+	int nr;
+	int err;
+} rs;
+
+static void rsyscall_handler(int sig, siginfo_t *si, void *ctx)
+{
+	if (rs.cnt == libc.threads_minus_1) return;
+
+	if (syscall6(rs.nr, rs.arg[0], rs.arg[1], rs.arg[2],
+		rs.arg[3], rs.arg[4], rs.arg[5]) < 0 && !rs.err) rs.err=errno;
+
+	a_inc(&rs.cnt);
+	__wake(&rs.cnt, 1, 1);
+	while(rs.hold)
+		__wait(&rs.hold, 0, 1, 1);
+	a_dec(&rs.cnt);
+	if (!rs.cnt) __wake(&rs.cnt, 1, 1);
+}
+
+static int rsyscall(int nr, long a, long b, long c, long d, long e, long f)
+{
+	int i, ret;
+	sigset_t set = { 0 };
+	struct pthread *self = pthread_self();
+	sigaddset(&set, SIGSYSCALL);
+
+	LOCK(&rs.lock);
+	while ((i=rs.blocks))
+		__wait(&rs.blocks, 0, i, 1);
+
+	__libc_sigprocmask(SIG_BLOCK, &set, 0);
+
+	rs.nr = nr;
+	rs.arg[0] = a; rs.arg[1] = b;
+	rs.arg[2] = c; rs.arg[3] = d;
+	rs.arg[4] = d; rs.arg[5] = f;
+	rs.hold = 1;
+	rs.err = 0;
+	rs.cnt = 0;
+
+	/* Dispatch signals until all threads respond */
+	for (i=libc.threads_minus_1; i; i--)
+		sigqueue(self->pid, SIGSYSCALL, (union sigval){0});
+	while ((i=rs.cnt) < libc.threads_minus_1) {
+		sigqueue(self->pid, SIGSYSCALL, (union sigval){0});
+		__wait(&rs.cnt, 0, i, 1);
+	}
+
+	/* Handle any lingering signals with no-op */
+	__libc_sigprocmask(SIG_UNBLOCK, &set, 0);
+
+	/* Resume other threads' signal handlers and wait for them */
+	rs.hold = 0;
+	__wake(&rs.hold, -1, 0);
+	while((i=rs.cnt)) __wait(&rs.cnt, 0, i, 1);
+
+	if (rs.err) errno = rs.err, ret = -1;
+	else ret = syscall6(nr, a, b, c, d, e, f);
+
+	UNLOCK(&rs.lock);
+	return ret;
+}
+
+static void cancelpt(int x)
+{
+	struct pthread *self = pthread_self();
+	if (self->canceldisable) return;
+	self->cancelpoint = x;
+	if (self->cancel) docancel(self);
+}
+
+static void init_threads()
+{
+	struct sigaction sa = { .sa_flags = SA_SIGINFO | SA_RESTART };
+	libc.lock = __lock;
+	libc.cancelpt = cancelpt;
+	libc.rsyscall = rsyscall;
+	sa.sa_sigaction = cancel_handler;
+	__libc_sigaction(SIGCANCEL, &sa, 0);
+	sigaddset(&sa.sa_mask, SIGSYSCALL);
+	sigaddset(&sa.sa_mask, SIGCANCEL);
+	sa.sa_sigaction = rsyscall_handler;
+	__libc_sigaction(SIGSYSCALL, &sa, 0);
+	sigprocmask(SIG_UNBLOCK, &sa.sa_mask, 0);
+}
+
+static int start(void *p)
+{
+	struct pthread *self = p;
+	pthread_exit(self->start(self->start_arg));
+	return 0;
+}
+
+#undef pthread_self
+
+#define CLONE_MAGIC 0x7d0f00
+int __clone(int (*)(void *), void *, int, void *, pid_t *, void *, pid_t *);
+
+#define ROUND(x) (((x)+PAGE_SIZE-1)&-PAGE_SIZE)
+
+/* pthread_key_create.c overrides this */
+static const size_t dummy = 0;
+weak_alias(dummy, __pthread_tsd_size);
+
+int pthread_create(pthread_t *res, const pthread_attr_t *attr, void *(*entry)(void *), void *arg)
+{
+	static int init;
+	int ret;
+	size_t size, guard;
+	struct pthread *self = pthread_self(), *new;
+	unsigned char *map, *stack, *tsd;
+	static const pthread_attr_t default_attr;
+
+	if (!self) return errno = ENOSYS;
+	if (!init && ++init) init_threads();
+
+	if (!attr) attr = &default_attr;
+	guard = ROUND(attr->__guardsize + DEFAULT_GUARD_SIZE);
+	size = guard + ROUND(attr->__stacksize + DEFAULT_STACK_SIZE);
+	size += __pthread_tsd_size;
+	map = mmap(0, size, PROT_READ|PROT_WRITE|PROT_EXEC, MAP_PRIVATE|MAP_ANON, -1, 0);
+	if (!map) return EAGAIN;
+	mprotect(map, guard, PROT_NONE);
+
+	tsd = map + size - __pthread_tsd_size;
+	new = (void *)(tsd - sizeof *new - PAGE_SIZE%sizeof *new);
+	new->map_base = map;
+	new->map_size = size;
+	new->pid = self->pid;
+	new->errno_ptr = &new->errno_val;
+	new->start = entry;
+	new->start_arg = arg;
+	new->self = new;
+	new->tsd = (void *)tsd;
+	new->detached = attr->__detach;
+	new->attr = *attr;
+	memcpy(new->tlsdesc, self->tlsdesc, sizeof new->tlsdesc);
+	new->tlsdesc[1] = (uintptr_t)new;
+	stack = (void *)((uintptr_t)new-1 & ~(uintptr_t)15);
+
+	/* We must synchronize new thread creation with rsyscall
+	 * delivery. This looks to be the least expensive way: */
+	a_inc(&rs.blocks);
+	while (rs.lock) __wait(&rs.lock, 0, 1, 1);
+
+	a_inc(&libc.threads_minus_1);
+	ret = __clone(start, stack, CLONE_MAGIC, new,
+		&new->tid, &new->tlsdesc, &new->tid);
+
+	a_dec(&rs.blocks);
+	if (rs.lock) __wake(&rs.blocks, 1, 1);
+
+	if (ret < 0) {
+		a_dec(&libc.threads_minus_1);
+		munmap(map, size);
+		return -ret;
+	}
+	*res = new;
+	return 0;
+}