libc: kvx: add {get,set,swap,make}context functions

Add the obsolescent SUSv3 family of user context manipulating functions
for kvx.

Signed-off-by: Julian Vetter <jvetter@kalrayinc.com>

1 files changed, 53 insertions, 0 deletions

diff --git a/libc/sysdeps/linux/kvx/makecontext.c b/libc/sysdeps/linux/kvx/makecontext.c
new file mode 100644
index 000000000..a52eded9f
--- /dev/null
+++ b/libc/sysdeps/linux/kvx/makecontext.c
@@ -0,0 +1,53 @@
+/*
+ * This file is subject to the terms and conditions of the GNU General Public
+ * License. See the file "COPYING" in the main directory of this archive for
+ * more details.
+ *
+ * Copyright (C) 2025 Kalray Inc.
+ * Author(s): Julian Vetter <jvetter@kalrayinc.com>
+ */
+
+#include <stdarg.h>
+#include <ucontext.h>
+
+
+/* Number of arguments that go in registers.	*/
+#define NREG_ARGS 12
+
+/* Take a context previously prepared via getcontext() and set to
+	 call func() with the given int only args.	*/
+void
+__makecontext (ucontext_t *ucp, void (*func) (void), int argc, ...)
+{
+	extern void __startcontext (void);
+	unsigned long *funcstack;
+	va_list vl;
+	unsigned long *regptr;
+	unsigned int reg;
+
+	/* Start at the top of stack.	*/
+	funcstack = (unsigned long *) (ucp->uc_stack.ss_sp + ucp->uc_stack.ss_size);
+	funcstack -= argc < NREG_ARGS ? 0 : argc - NREG_ARGS;
+	funcstack = (unsigned long *) (((uintptr_t) funcstack & -32L));
+
+	ucp->uc_mcontext.sc_regs.r12 = (unsigned long) funcstack;
+	/* Use $r20 and $r21 to pass some infos to __startcontext */
+	ucp->uc_mcontext.sc_regs.r20 = (unsigned long) ucp->uc_link;
+	ucp->uc_mcontext.sc_regs.r21 = (unsigned long) func;
+	ucp->uc_mcontext.sc_regs.ra = (unsigned long) __startcontext;
+
+	va_start (vl, argc);
+
+	/* The first twelve arguments go into registers.	*/
+	regptr = &(ucp->uc_mcontext.sc_regs.r0);
+
+	for (reg = 0; (reg < argc) && (reg < NREG_ARGS); reg++)
+		*regptr++ = va_arg (vl, unsigned long);
+
+	/* And the remainder on the stack.	*/
+	for (; reg < argc; reg++)
+		*funcstack++ = va_arg (vl, unsigned long);
+
+	va_end (vl);
+}
+weak_alias (__makecontext, makecontext)