lib: Add mlibc

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

1 files changed, 68 insertions, 0 deletions

diff --git a/lib/mlibc/options/internal/gcc/guard-abi.cpp b/lib/mlibc/options/internal/gcc/guard-abi.cpp
new file mode 100644
index 0000000..945582a
--- /dev/null
+++ b/lib/mlibc/options/internal/gcc/guard-abi.cpp
@@ -0,0 +1,68 @@
+
+#include <stddef.h>
+#include <stdint.h>
+#include <string.h>
+
+#include <mlibc/debug.hpp>
+#include <mlibc/internal-sysdeps.hpp>
+
+namespace {
+
+// Itanium ABI static initialization guard.
+struct Guard {
+	// bit of the mutex member variable.
+	// indicates that the mutex is locked.
+	static constexpr int32_t locked = 1;
+
+	void lock() {
+		uint32_t v = 0;
+		if(__atomic_compare_exchange_n(&mutex, &v, Guard::locked, false,
+				__ATOMIC_ACQUIRE, __ATOMIC_RELAXED))
+			return;
+
+		mlibc::sys_libc_log("__cxa_guard_acquire contention");
+		__builtin_trap();
+	}
+
+	void unlock() {
+		__atomic_store_n(&mutex, 0, __ATOMIC_RELEASE);
+	}
+
+	// the first byte's meaning is fixed by the ABI.
+	// it indicates whether initialization has already been completed.
+	uint8_t complete;
+
+	// we use some of the remaining bytes to implement a mutex.
+	uint32_t mutex;
+};
+
+static_assert(sizeof(Guard) == sizeof(int64_t));
+
+} // namespace { }
+
+extern "C" [[ gnu::visibility("hidden") ]] void __cxa_pure_virtual() {
+	mlibc::panicLogger() << "mlibc: Pure virtual function called from IP "
+			<< (void *)__builtin_return_address(0) << frg::endlog;
+}
+
+extern "C" [[ gnu::visibility("hidden") ]] int __cxa_guard_acquire(int64_t *ptr) {
+	auto guard = reinterpret_cast<Guard *>(ptr);
+	guard->lock();
+	// relaxed ordering is sufficient because
+	// Guard::complete is only modified while the mutex is held.
+	if(__atomic_load_n(&guard->complete, __ATOMIC_RELAXED)) {
+		guard->unlock();
+		return 0;
+	}else{
+		return 1;
+	}
+}
+
+extern "C" [[ gnu::visibility("hidden") ]] void __cxa_guard_release(int64_t *ptr) {
+	auto guard = reinterpret_cast<Guard *>(ptr);
+	// do a store-release so that compiler generated code can skip calling
+	// __cxa_guard_acquire by doing a load-acquire on Guard::complete.
+	__atomic_store_n(&guard->complete, 1, __ATOMIC_RELEASE);
+	guard->unlock();
+}
+