1 #include "threadimpl.h"
2 
3 void
4 makecontext(ucontext_t *uc, void (*fn)(void), int argc, ...)
5 {
6 	uintptr *sp;
7 	va_list arg;
8 
9 //fprint(2, "makecontext %d\n", argc);
10 	if(argc != 2)
11 		sysfatal("libthread: makecontext misused");
12 	va_start(arg, argc);
13 	uc->mc.di = va_arg(arg, uint);
14 	uc->mc.si = va_arg(arg, uint);
15 //fprint(2, "%ux %ux\n", uc->mc.di, uc->mc.si);
16 	va_end(arg);
17 
18 	sp = (uintptr*)((char*)uc->uc_stack.ss_sp+uc->uc_stack.ss_size);
19 	/*
20 	 * Stack pointer at call instruction (before return address
21 	 * gets pushed) must be 16-byte aligned.
22 	 */
23 	if((uintptr)sp%4)
24 		abort();
25 	while((uintptr)sp%16 != 0)
26 		sp--;
27 	*--sp = 0;  // fn's return address
28 	*--sp = (uintptr)fn;  // return address of setcontext
29 	uc->mc.sp = (uintptr)sp;
30 }
31 
32 int
33 swapcontext(ucontext_t *oucp, ucontext_t *ucp)
34 {
35 	if(getcontext(oucp) == 0)
36 		setcontext(ucp);
37 	return 0;
38 }