libthread: use consistent stack calculation code in makecontext

Also reduce duplication: makecontext is per-arch not per-os-arch.

May fix #353.

1 files changed, 28 insertions, 0 deletions

diff --git a/src/libthread/x86_64-ucontext.c b/src/libthread/x86_64-ucontext.c
new file mode 100644
index 00000000..5d1aaefc
--- /dev/null
+++ b/src/libthread/x86_64-ucontext.c
@@ -0,0 +1,28 @@
+#include "threadimpl.h"
+
+void
+makecontext(ucontext_t *uc, void (*fn)(void), int argc, ...)
+{
+	uintptr *sp;
+	va_list arg;
+
+	if(argc != 2)
+		sysfatal("libthread: makecontext misused");
+	va_start(arg, argc);
+	uc->mc.di = va_arg(arg, uint);
+	uc->mc.si = va_arg(arg, uint);
+	va_end(arg);
+
+	sp = USPALIGN(uc, 16);
+	*--sp = 0;  // fn's return address
+	*--sp = (uintptr)fn;  // return address of setcontext
+	uc->mc.sp = (uintptr)sp;
+}
+
+int
+swapcontext(ucontext_t *oucp, ucontext_t *ucp)
+{
+	if(getcontext(oucp) == 0)
+		setcontext(ucp);
+	return 0;
+}