From e11fa34822ac4e3e5848dac03b5420fe00c64b05 Mon Sep 17 00:00:00 2001
From: Ariadne Conill <ariadne@dereferenced.org>
Date: Mon, 18 May 2020 03:19:22 +0000
Subject: [PATCH] riscv64: add makecontext() and __start_context() trampoline

---
 arch/riscv64/makecontext.c  | 62 +++++++++++++++++++++++++++++++++++++
 arch/riscv64/startcontext.S | 29 +++++++++++++++++
 2 files changed, 91 insertions(+)
 create mode 100644 arch/riscv64/makecontext.c
 create mode 100644 arch/riscv64/startcontext.S

diff --git a/arch/riscv64/makecontext.c b/arch/riscv64/makecontext.c
new file mode 100644
index 0000000..7325a9a
--- /dev/null
+++ b/arch/riscv64/makecontext.c
@@ -0,0 +1,62 @@
+/*
+ * Copyright (c) 2018 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 <signal.h>
+#include <string.h>
+#include <stdint.h>
+#include <stdio.h>
+#include "defs.h"
+
+
+extern void __start_context(void);
+
+
+void
+__makecontext(ucontext_t *ucp, void (*func)(void), int argc, ...)
+{
+	greg_t *sp, *regp;
+	va_list va;
+	int i;
+
+	/* set up and align the stack. */
+	sp = (greg_t *) ((uintptr_t) ucp->uc_stack.ss_sp + ucp->uc_stack.ss_size);
+	sp -= argc < 8 ? 0 : argc - 8;
+	sp = (greg_t *) (((uintptr_t) sp & -16L));
+
+	/* set up the ucontext structure */
+	ucp->uc_mcontext.gregs[REG_PC] = (greg_t) __start_context;
+	ucp->uc_mcontext.gregs[REG_S0] = 0;
+	ucp->uc_mcontext.gregs[REG_S1] = (greg_t) func;
+	ucp->uc_mcontext.gregs[REG_S2] = (greg_t) ucp->uc_link;
+	ucp->uc_mcontext.gregs[REG_SP] = (greg_t) sp;
+	ucp->uc_mcontext.gregs[REG_PC_SAVE] = 0;
+
+	va_start(va, argc);
+
+	/* first 8 args go in $a0 through $a7. */
+	regp = &(ucp->uc_mcontext.gregs[REG_A0]);
+
+	for (i = 0; (i < argc && i < 8); i++)
+		*regp++ = va_arg (va, greg_t);
+
+	/* remainder overflows into stack */
+	for (; i < argc; i++)
+		*sp++ = va_arg (va, greg_t);
+
+	va_end(va);
+}
+
+
+extern __typeof(__makecontext) makecontext __attribute__((weak, __alias__("__makecontext")));
diff --git a/arch/riscv64/startcontext.S b/arch/riscv64/startcontext.S
new file mode 100644
index 0000000..9a885c8
--- /dev/null
+++ b/arch/riscv64/startcontext.S
@@ -0,0 +1,29 @@
+/*
+ * 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.
+ */
+
+#include "defs.h"
+
+FUNC(__start_context)
+	/* call the function passed to makecontext() */
+	jalr	s1
+
+	/* check for linked context */
+	beqz	s2, no_linked_context
+
+	/* if one is set, invoke it */
+	mv	a0, s2
+	jal	__setcontext
+
+	/* otherwise, exit. */
+no_linked_context:
+	j	exit
+END(__start_context)