1 files changed, 89 insertions, 0 deletions
diff --git a/src/ldso/dlerror.c b/src/ldso/dlerror.c
new file mode 100644
index 0000000..dae0f3a
--- /dev/null
+++ b/src/ldso/dlerror.c
@@ -0,0 +1,89 @@
+#include <dlfcn.h>
+#include <stdlib.h>
+#include <stdarg.h>
+#include "pthread_impl.h"
+#include "dynlink.h"
+#include "atomic.h"
+
+#define malloc __libc_malloc
+#define calloc __libc_calloc
+#define realloc __libc_realloc
+#define free __libc_free
+
+char *dlerror()
+{
+	pthread_t self = __pthread_self();
+	if (!self->dlerror_flag) return 0;
+	self->dlerror_flag = 0;
+	char *s = self->dlerror_buf;
+	if (s == (void *)-1)
+		return "Dynamic linker failed to allocate memory for error message";
+	else
+		return s;
+}
+
+/* Atomic singly-linked list, used to store list of thread-local dlerror
+ * buffers for deferred free. They cannot be freed at thread exit time
+ * because, by the time it's known they can be freed, the exiting thread
+ * is in a highly restrictive context where it cannot call (even the
+ * libc-internal) free. It also can't take locks; thus the atomic list. */
+
+static void *volatile freebuf_queue;
+
+void __dl_thread_cleanup(void)
+{
+	pthread_t self = __pthread_self();
+	if (!self->dlerror_buf || self->dlerror_buf == (void *)-1)
+		return;
+	void *h;
+	do {
+		h = freebuf_queue;
+		*(void **)self->dlerror_buf = h;
+	} while (a_cas_p(&freebuf_queue, h, self->dlerror_buf) != h);
+}
+
+hidden void __dl_vseterr(const char *fmt, va_list ap)
+{
+	void **q;
+	do q = freebuf_queue;
+	while (q && a_cas_p(&freebuf_queue, q, 0) != q);
+
+	while (q) {
+		void **p = *q;
+		free(q);
+		q = p;
+	}
+
+	va_list ap2;
+	va_copy(ap2, ap);
+	pthread_t self = __pthread_self();
+	if (self->dlerror_buf != (void *)-1)
+		free(self->dlerror_buf);
+	size_t len = vsnprintf(0, 0, fmt, ap2);
+	if (len < sizeof(void *)) len = sizeof(void *);
+	va_end(ap2);
+	char *buf = malloc(len+1);
+	if (buf) {
+		vsnprintf(buf, len+1, fmt, ap);
+	} else {
+		buf = (void *)-1;	
+	}
+	self->dlerror_buf = buf;
+	self->dlerror_flag = 1;
+}
+
+hidden void __dl_seterr(const char *fmt, ...)
+{
+	va_list ap;
+	va_start(ap, fmt);
+	__dl_vseterr(fmt, ap);
+	va_end(ap);
+}
+
+static int stub_invalid_handle(void *h)
+{
+	__dl_seterr("Invalid library handle %p", (void *)h);
+	return 1;
+}
+
+weak_alias(stub_invalid_handle, __dl_invalid_handle);