lib: Add mlibc

Signed-off-by: Ian Moffett <ian@osmora.org>

1 files changed, 114 insertions, 0 deletions

diff --git a/lib/mlibc/options/posix/generic/semaphore-stubs.cpp b/lib/mlibc/options/posix/generic/semaphore-stubs.cpp
new file mode 100644
index 0000000..d41eccb
--- /dev/null
+++ b/lib/mlibc/options/posix/generic/semaphore-stubs.cpp
@@ -0,0 +1,114 @@
+#include <semaphore.h>
+#include <errno.h>
+
+#include <bits/ensure.h>
+#include <mlibc/debug.hpp>
+#include <mlibc/ansi-sysdeps.hpp>
+#include <mlibc/posix-sysdeps.hpp>
+
+static constexpr unsigned int semaphoreHasWaiters = static_cast<uint32_t>(1 << 31);
+static constexpr unsigned int semaphoreCountMask = static_cast<uint32_t>(1 << 31) - 1;
+
+int sem_init(sem_t *sem, int pshared, unsigned int initial_count) {
+	if (pshared) {
+		mlibc::infoLogger() << "mlibc: shared semaphores are unsuppored" << frg::endlog;
+		errno = ENOSYS;
+		return -1;
+	}
+
+	if (initial_count > SEM_VALUE_MAX) {
+		errno = EINVAL;
+		return -1;
+	}
+
+	sem->__mlibc_count = initial_count;
+
+	return 0;
+}
+
+int sem_destroy(sem_t *) {
+	return 0;
+}
+
+int sem_wait(sem_t *sem) {
+	unsigned int state = 0;
+
+	while (1) {
+		if (!(state & semaphoreCountMask)) {
+			if (__atomic_compare_exchange_n(&sem->__mlibc_count, &state, semaphoreHasWaiters,
+						false, __ATOMIC_ACQUIRE, __ATOMIC_ACQUIRE)) {
+				int e = mlibc::sys_futex_wait((int *)&sem->__mlibc_count, state, nullptr);
+				if (e == 0 || e == EAGAIN) {
+					continue;
+				} else if (e == EINTR) {
+					errno = EINTR;
+					return -1;
+				} else {
+					mlibc::panicLogger() << "sys_futex_wait() failed with error code " << e << frg::endlog;
+				}
+			}
+		} else {
+			unsigned int desired = (state - 1);
+			if (__atomic_compare_exchange_n(&sem->__mlibc_count, &state, desired, false,
+						__ATOMIC_RELAXED, __ATOMIC_RELAXED))
+				return 0;
+		}
+	}
+}
+
+int sem_timedwait(sem_t *sem, const struct timespec *) {
+	mlibc::infoLogger() << "\e[31mmlibc: sem_timedwait is implemented as sem_wait\e[0m" << frg::endlog;
+	return sem_wait(sem);
+}
+
+int sem_post(sem_t *sem) {
+	auto old_count = __atomic_load_n(&sem->__mlibc_count, __ATOMIC_RELAXED) & semaphoreCountMask;
+
+	if (old_count + 1 > SEM_VALUE_MAX) {
+		errno = EOVERFLOW;
+		return -1;
+	}
+
+	auto state = __atomic_exchange_n(&sem->__mlibc_count, old_count + 1, __ATOMIC_RELEASE);
+
+	if (state & semaphoreHasWaiters)
+		if (int e = mlibc::sys_futex_wake((int *)&sem->__mlibc_count); e)
+			__ensure(!"sys_futex_wake() failed");
+
+	return 0;
+}
+
+sem_t *sem_open(const char *, int, ...) {
+	__ensure(!"Not implemented");
+	__builtin_unreachable();
+}
+
+int sem_close(sem_t *) {
+	__ensure(!"Not implemented");
+	__builtin_unreachable();
+}
+
+int sem_getvalue(sem_t *, int *) {
+	__ensure(!"Not implemented");
+	__builtin_unreachable();
+}
+
+int sem_unlink(const char *) {
+	__ensure(!"Not implemented");
+	__builtin_unreachable();
+}
+
+int sem_trywait(sem_t *sem) {
+	while (true) {
+		auto state = __atomic_load_n(&sem->__mlibc_count, __ATOMIC_ACQUIRE);
+
+		if (state & semaphoreHasWaiters) {
+			return EAGAIN;
+		}
+
+		auto desired = state - 1;
+		if (__atomic_compare_exchange_n(&sem->__mlibc_count, &state, desired, false, __ATOMIC_RELEASE, __ATOMIC_RELAXED)) {
+			return 0;
+		}
+	}
+}