1 files changed, 59 insertions, 8 deletions
diff --git a/lib/libc/gen/errno.c b/lib/libc/gen/errno.c
index 62c0978c6aa..d706b0807a7 100644
--- a/lib/libc/gen/errno.c
+++ b/lib/libc/gen/errno.c
@@ -1,21 +1,72 @@
-/*	$OpenBSD: errno.c,v 1.5 2005/08/08 08:05:34 espie Exp $ */
+/*	$OpenBSD: errno.c,v 1.6 2016/05/07 19:05:22 guenther Exp $ */
 /* PUBLIC DOMAIN: No Rights Reserved.   Marco S Hyman <marc@snafu.org> */
 
+#include <tib.h>
 #include <errno.h>
-#undef errno
+#include <unistd.h>
+#include "thread_private.h"
 
+
+#ifdef TCB_HAVE_MD_GET
 /*
- * global errno for unthreaded programs.
+ * If there's an MD TCB_GET() macro, then getting the TCB address is
+ * cheap enough that we can do it even in single-threaded programs,
+ * so the tc_errnoptr and tc_tcb callbacks will be unused, and __errno()
+ * can just use TIB_GET().
  */
-int errno;
+int *
+__errno(void)
+{
+	return (&TIB_GET()->tib_errno);
+}
+DEF_STRONG(__errno);
 
+#else /* ! TCB_HAVE_MD_GET */
 /*
- * weak version of function used by unthreaded programs.
+ * Otherwise, getting the TCB address requires the __get_tcb()
+ * syscall.  Rather than pay that cost for single-threaded programs,
+ * the syscall stubs will invoke the tc_errnoptr callback to set errno
+ * and other code will invoke the tc_tcb callback to get the TCB
+ * for cancelation checks, etc.  The default callbacks will just
+ * work from the cached location of the initial thread's TCB;
+ * libpthread can override them to the necessary more expensive
+ * versions that use __get_tcb().
+ */
+
+/* cached pointer to the TCB of the only thread in single-threaded programs */
+void	*_libc_single_tcb = NULL;
+
+static inline void *
+single_threaded_tcb(void)
+{
+	if (__predict_false(_libc_single_tcb == NULL))
+		_libc_single_tcb = TCB_GET();
+	return (_libc_single_tcb);
+}
+
+static int *
+single_threaded_errnoptr(void)
+{
+	return &TCB_TO_TIB(single_threaded_tcb())->tib_errno;
+}
+
+/*
+ * __errno(): just use the callback to get the applicable current method
  */
 int *
-___errno(void)
+__errno(void)
 {
-	return &errno;
+	return (_thread_cb.tc_errnoptr());
 }
+DEF_STRONG(__errno);
+
+#endif /* !TCB_HAVE_MD_GET */
 
-__weak_alias(__errno, ___errno);
+
+struct thread_callbacks _thread_cb =
+{
+#ifndef	TCB_HAVE_MD_GET
+	.tc_errnoptr	= &single_threaded_errnoptr,
+	.tc_tcb		= &single_threaded_tcb,
+#endif
+};