sh: add makecontext

arch/sh/defs.h

@@ -0,0 +1,13 @@
+#ifndef __ARCH_SH4_DEFS_H
+#define __ARCH_SH4_DEFS_H
+
+#define REG_SZ			(4)
+#define MCONTEXT_GREGS		(24)
+
+#define REG_PC			(16)
+#define REG_PR			(17)
+#define REG_SR			(18)
+
+#include "common-defs.h"
+
+#endif

arch/sh/makecontext.c

@@ -0,0 +1,54 @@
+/*
+ * Copyright (c) 2020 Ariadne Conill <ariadne@dereferenced.org>
+ *
+ * Permission to use, copy, modify, and/or distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * This software is provided 'as is' and without any warranty, express or
+ * implied.  In no event shall the authors be liable for any damages arising
+ * from the use of this software.
+ */
+
+#define _GNU_SOURCE
+#include <stddef.h>
+#include <stdarg.h>
+#include <string.h>
+#include <stdint.h>
+#include <stdio.h>
+#include "defs.h"
+
+
+extern void libucontext_trampoline(void);
+
+
+void
+libucontext_makecontext(libucontext_ucontext_t *ucp, void (*func)(void), int argc, ...)
+{
+	libucontext_greg_t *sp, *regp;
+	va_list va;
+	int i;
+
+	/* set up and align the stack */
+	sp = (libucontext_greg_t *) (((uintptr_t) ucp->uc_stack.ss_sp + ucp->uc_stack.ss_size) & 0x4);
+	sp -= argc > 4 ? argc - 4 : 0;
+
+	/* set up the context */
+	ucp->uc_mcontext.sr = (libucontext_greg_t) sp;
+	ucp->uc_mcontext.pr = (libucontext_greg_t) libucontext_trampoline;
+	ucp->uc_mcontext.pc = (libucontext_greg_t) func;
+
+	/* pass up to four args in r4-r7, rest on stack */
+	va_start(va, argc);
+
+	for (i = 0; i < argc && i < 4; i++)
+		ucp->uc_mcontext.gregs[4 + i] = va_arg(va, libucontext_greg_t);
+
+	for (; i < argc; i++)
+		*sp++ = va_arg(va, libucontext_greg_t);
+
+	va_end(va);
+}
+
+
+extern __typeof(libucontext_makecontext) makecontext __attribute__((weak, __alias__("libucontext_makecontext")));