diff options
Diffstat (limited to 'src/thread')
| -rw-r--r-- | src/thread/__rsyscall.c | 113 | ||||
| -rw-r--r-- | src/thread/pthread_create.c | 105 |
2 files changed, 122 insertions, 96 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); +} diff --git a/src/thread/pthread_create.c b/src/thread/pthread_create.c index a9a08171..ec329f50 100644 --- a/src/thread/pthread_create.c +++ b/src/thread/pthread_create.c @@ -1,5 +1,11 @@ #include "pthread_impl.h" +static void dummy_0() +{ +} +weak_alias(dummy_0, __rsyscall_lock); +weak_alias(dummy_0, __rsyscall_unlock); + static void dummy_1(pthread_t self) { } @@ -72,101 +78,12 @@ static void cancelpt(int x) } } -/* "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) -{ - 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); -} - -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.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, 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 = syscall(nr, a, b, c, d, e, f); - - UNLOCK(&rs.lock); - return ret; -} - static void init_threads() { struct sigaction sa = { .sa_flags = SA_SIGINFO | SA_RESTART }; libc.lock = __lock; libc.lockfile = __lockfile; libc.cancelpt = cancelpt; - libc.rsyscall = rsyscall; - - sigfillset(&sa.sa_mask); - sa.sa_sigaction = rsyscall_handler; - __libc_sigaction(SIGSYSCALL, &sa, 0); sigemptyset(&sa.sa_mask); sa.sa_sigaction = cancel_handler; @@ -205,7 +122,7 @@ int pthread_create(pthread_t *res, const pthread_attr_t *attr, void *(*entry)(vo size_t size, guard; struct pthread *self = pthread_self(), *new; unsigned char *map, *stack, *tsd; - static const pthread_attr_t default_attr; + const pthread_attr_t default_attr = { 0 }; if (!self) return ENOSYS; if (!init && ++init) init_threads(); @@ -236,16 +153,12 @@ 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); - /* 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); + __rsyscall_lock(); a_inc(&libc.threads_minus_1); ret = __uniclone(stack, start, new); - a_dec(&rs.blocks); - if (rs.lock) __wake(&rs.blocks, 1, 1); + __rsyscall_unlock(); if (ret < 0) { a_dec(&libc.threads_minus_1); |