3 files changed, 113 insertions, 118 deletions

diff --git a/src/thread/__rsyscall.c b/src/thread/__rsyscall.c
deleted file mode 100644
index e885d9e7..00000000
--- a/src/thread/__rsyscall.c
+++ /dev/null
@@ -1,114 +0,0 @@
-#include "pthread_impl.h"
-
-/* "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;
-	int init;
-} rs;
-
-static void rsyscall_handler(int sig, siginfo_t *si, void *ctx)
-{
-	struct pthread *self = __pthread_self();
-	long r;
-
-	if (!rs.hold || rs.cnt == libc.threads_minus_1) return;
-
-	/* Threads which have already decremented themselves from the
-	 * thread count must not increment rs.cnt or otherwise act. */
-	if (self->dead) {
-		sigfillset(&((ucontext_t *)ctx)->uc_sigmask);
-		return;
-	}
-
-	r = __syscall(rs.nr, rs.arg[0], rs.arg[1],
-		rs.arg[2], rs.arg[3], rs.arg[4], rs.arg[5]);
-	if (r < 0) rs.err=-r;
-
-	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);
-}
-
-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;
-
-	if (!libc.threads_minus_1)
-		return syscall(nr, a, b, c, d, e, f);
-
-	self = __pthread_self();
-
-	LOCK(&rs.lock);
-	while ((i=rs.blocks))
-		__wait(&rs.blocks, 0, i, 1);
-
-	__syscall(SYS_rt_sigprocmask, SIG_BLOCK, (uint64_t[]){-1}, &set, 8);
-
-	if (!rs.init) {
-		struct sigaction sa = {
-			.sa_flags = SA_SIGINFO | SA_RESTART,
-			.sa_sigaction = rsyscall_handler,
-			.sa_mask = set
-		};
-		sigfillset(&sa.sa_mask);
-		sa.sa_sigaction = rsyscall_handler;
-		__libc_sigaction(SIGSYSCALL, &sa, 0);
-		rs.init = 1;
-	}
-
-	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.err = 0;
-	rs.cnt = 0;
-	rs.hold = 1;
-
-	/* 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 */
-	__syscall(SYS_rt_sigprocmask, SIG_SETMASK, &set, &set, 8);
-
-	/* 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 = syscall(nr, a, b, c, d, e, f);
-
-	UNLOCK(&rs.lock);
-	return ret;
-}
-
-void __rsyscall_lock()
-{
-	a_inc(&rs.blocks);
-	while (rs.lock) __wait(&rs.lock, 0, 1, 1);
-}
-
-void __rsyscall_unlock()
-{
-	a_dec(&rs.blocks);
-	if (rs.lock) __wake(&rs.blocks, 1, 1);
-}
diff --git a/src/thread/pthread_create.c b/src/thread/pthread_create.c
index d60c2a4d..856015ff 100644
--- a/src/thread/pthread_create.c
+++ b/src/thread/pthread_create.c
@@ -3,8 +3,8 @@
 static void dummy_0()
 {
 }
-weak_alias(dummy_0, __rsyscall_lock);
-weak_alias(dummy_0, __rsyscall_unlock);
+weak_alias(dummy_0, __synccall_lock);
+weak_alias(dummy_0, __synccall_unlock);
 weak_alias(dummy_0, __pthread_tsd_run_dtors);
 
 #ifdef __pthread_unwind_next
@@ -99,12 +99,12 @@ int pthread_create(pthread_t *res, const pthread_attr_t *attr, void *(*entry)(vo
 	new->tlsdesc[1] = (uintptr_t)new;
 	stack = (void *)((uintptr_t)new-1 & ~(uintptr_t)15);
 
-	__rsyscall_lock();
+	__synccall_lock();
 
 	a_inc(&libc.threads_minus_1);
 	ret = __uniclone(stack, start, new);
 
-	__rsyscall_unlock();
+	__synccall_unlock();
 
 	if (ret < 0) {
 		a_dec(&libc.threads_minus_1);
diff --git a/src/thread/synccall.c b/src/thread/synccall.c
new file mode 100644
index 00000000..7c4f92bf
--- /dev/null
+++ b/src/thread/synccall.c
@@ -0,0 +1,109 @@
+#include "pthread_impl.h"
+#include <semaphore.h>
+
+static struct chain {
+	struct chain *next;
+	sem_t sem, sem2;
+} *head;
+
+static void (*callback)(void *), *context;
+static int chainlen;
+static sem_t chainlock, chaindone;
+static pthread_rwlock_t lock = PTHREAD_RWLOCK_INITIALIZER;
+
+static void handler(int sig, siginfo_t *si, void *ctx)
+{
+	struct chain ch;
+	pthread_t self = __pthread_self();
+	int old_errno = errno;
+
+	if (chainlen == libc.threads_minus_1) return;
+
+	sigqueue(self->pid, SIGSYNCCALL, (union sigval){0});
+
+	/* Threads which have already decremented themselves from the
+	 * thread count must not act. Block further receipt of signals
+	 * and return. */
+	if (self->dead) {
+		memset(&((ucontext_t *)ctx)->uc_sigmask, -1, 8);
+		errno = old_errno;
+		return;
+	}
+
+	sem_init(&ch.sem, 0, 0);
+	sem_init(&ch.sem2, 0, 0);
+
+	while (sem_wait(&chainlock));
+	ch.next = head;
+	head = &ch;
+	if (++chainlen == libc.threads_minus_1) sem_post(&chaindone);
+	sem_post(&chainlock);
+
+	while (sem_wait(&ch.sem));
+	callback(context);
+	sem_post(&ch.sem2);
+	while (sem_wait(&ch.sem));
+
+	errno = old_errno;
+}
+
+void __synccall(void (*func)(void *), void *ctx)
+{
+	pthread_t self;
+	struct sigaction sa;
+	struct chain *cur, *next;
+	uint64_t oldmask;
+
+	pthread_rwlock_wrlock(&lock);
+
+	__syscall(SYS_rt_sigprocmask, SIG_BLOCK, (uint64_t[]){-1}, &oldmask, 8);
+
+	if (!libc.threads_minus_1) {
+		func(ctx);
+		return;
+	}
+
+	sem_init(&chaindone, 0, 0);
+	sem_init(&chainlock, 0, 1);
+	chainlen = 0;
+	callback = func;
+	context = ctx;
+
+	sa.sa_flags = SA_SIGINFO | SA_RESTART;
+	sa.sa_sigaction = handler;
+	sigfillset(&sa.sa_mask);
+	__libc_sigaction(SIGSYNCCALL, &sa, 0);
+
+	self = __pthread_self();
+	sigqueue(self->pid, SIGSYNCCALL, (union sigval){0});
+	while (sem_wait(&chaindone));
+
+	for (cur=head; cur; cur=cur->next) {
+		sem_post(&cur->sem);
+		while (sem_wait(&cur->sem2));
+	}
+	func(ctx);
+
+	for (cur=head; cur; cur=next) {
+		next = cur->next;
+		sem_post(&cur->sem);
+	}
+
+	sa.sa_flags = 0;
+	sa.sa_handler = SIG_IGN;
+	__libc_sigaction(SIGSYNCCALL, &sa, 0);
+
+	__syscall(SYS_rt_sigprocmask, SIG_SETMASK, &oldmask, 0, 8);
+
+	pthread_rwlock_unlock(&lock);
+}
+
+void __synccall_lock()
+{
+	pthread_rwlock_rdlock(&lock);
+}
+
+void __synccall_unlock()
+{
+	pthread_rwlock_unlock(&lock);
+}