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#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);
}
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