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-rw-r--r--src/thread/__rsyscall.c113
1 files changed, 113 insertions, 0 deletions
diff --git a/src/thread/__rsyscall.c b/src/thread/__rsyscall.c
new file mode 100644
index 00000000..923db2bf
--- /dev/null
+++ b/src/thread/__rsyscall.c
@@ -0,0 +1,113 @@
+#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);
+
+ sigfillset(&set);
+ __libc_sigprocmask(SIG_BLOCK, &set, &set);
+
+ if (!rs.init) {
+ struct sigaction sa = {
+ .sa_sigaction = rsyscall_handler,
+ .sa_mask = set
+ };
+ sigfillset(&sa.sa_mask);
+ sa.sa_sigaction = rsyscall_handler;
+ __libc_sigaction(SIGSYSCALL, &sa, 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.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 */
+ __libc_sigprocmask(SIG_UNBLOCK, &set, &set);
+
+ /* 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);
+}