From b507f65d4461757c577a9f90325967e92a895520 Mon Sep 17 00:00:00 2001
From: Samuel Williams <samuel.williams@oriontransfer.co.nz>
Date: Tue, 30 Mar 2021 18:46:24 +1300
Subject: Support for native riscv64 coroutines.

---
 configure.ac                |  3 ++
 coroutine/riscv64/Context.S | 87 +++++++++++++++++++++++++++++++++++++++++++++
 coroutine/riscv64/Context.h | 45 +++++++++++++++++++++++
 3 files changed, 135 insertions(+)
 create mode 100644 coroutine/riscv64/Context.S
 create mode 100644 coroutine/riscv64/Context.h

diff --git a/configure.ac b/configure.ac
index 58aa35a9da..d78964f63b 100644
--- a/configure.ac
+++ b/configure.ac
@@ -2488,6 +2488,9 @@ AS_CASE([$coroutine_type], [yes|''], [
         [powerpc64le-linux*], [
             coroutine_type=ppc64le
         ],
+        [riscv64-linux*], [
+            rb_cv_coroutine=riscv64
+        ],
         [x86_64-openbsd*], [
             coroutine_type=amd64
         ],
diff --git a/coroutine/riscv64/Context.S b/coroutine/riscv64/Context.S
new file mode 100644
index 0000000000..cc4e872f84
--- /dev/null
+++ b/coroutine/riscv64/Context.S
@@ -0,0 +1,87 @@
+#define TOKEN_PASTE(x,y) x##y
+#define PREFIXED_SYMBOL(prefix,name) TOKEN_PASTE(prefix,name)
+
+.text
+.align 2
+
+.global PREFIXED_SYMBOL(SYMBOL_PREFIX,coroutine_transfer)
+PREFIXED_SYMBOL(SYMBOL_PREFIX,coroutine_transfer):
+
+	# Make space on the stack for caller registers
+	addi sp, sp, -0xd0
+
+	# Save caller registers
+	sd s0, 0x00(sp)
+	sd s1, 0x08(sp)
+	sd s2, 0x10(sp)
+	sd s3, 0x18(sp)
+	sd s4, 0x20(sp)
+	sd s5, 0x28(sp)
+	sd s6, 0x30(sp)
+	sd s7, 0x38(sp)
+	sd s8, 0x40(sp)
+	sd s9, 0x48(sp)
+	sd s10, 0x50(sp)
+	sd s11, 0x58(sp)
+	fsd fs0, 0x60(sp)
+	fsd fs1, 0x68(sp)
+	fsd fs2, 0x70(sp)
+	fsd fs3, 0x78(sp)
+	fsd fs4, 0x80(sp)
+	fsd fs5, 0x88(sp)
+	fsd fs6, 0x90(sp)
+	fsd fs7, 0x98(sp)
+	fsd fs8, 0xa0(sp)
+	fsd fs9, 0xa8(sp)
+	fsd fs10, 0xb0(sp)
+	fsd fs11, 0xb8(sp)
+
+	# Save return address
+	sd ra, 0xc0(sp)
+
+	# Save stack pointer to a0 (first argument)
+	mv a2, sp
+	sd a2, (a0)
+
+	# Load stack pointer from a1 (second argument)
+	ld a3, (a1)
+	mv sp, a3
+
+	# Restore caller registers
+	ld s0, 0x00(sp)
+	ld s1, 0x08(sp)
+	ld s2, 0x10(sp)
+	ld s3, 0x18(sp)
+	ld s4, 0x20(sp)
+	ld s5, 0x28(sp)
+	ld s6, 0x30(sp)
+	ld s7, 0x38(sp)
+	ld s8, 0x40(sp)
+	ld s9, 0x48(sp)
+	ld s10, 0x50(sp)
+	ld s11, 0x58(sp)
+	fld fs0, 0x60(sp)
+	fld fs1, 0x68(sp)
+	fld fs2, 0x70(sp)
+	fld fs3, 0x78(sp)
+	fld fs4, 0x80(sp)
+	fld fs5, 0x88(sp)
+	fld fs6, 0x90(sp)
+	fld fs7, 0x98(sp)
+	fld fs8, 0xa0(sp)
+	fld fs9, 0xa8(sp)
+	fld fs10, 0xb0(sp)
+	fld fs11, 0xb8(sp)
+
+	# Load return address
+	ld ra, 0xc0(sp)
+
+	# Pop stack frame
+	addi sp, sp, 0xd0
+
+	# Jump to return address
+	ret
+
+#if defined(__linux__) && defined(__ELF__)
+.section .note.GNU-stack,"",%progbits
+#endif
diff --git a/coroutine/riscv64/Context.h b/coroutine/riscv64/Context.h
new file mode 100644
index 0000000000..5ec03266b2
--- /dev/null
+++ b/coroutine/riscv64/Context.h
@@ -0,0 +1,45 @@
+#pragma once
+
+#include <assert.h>
+#include <stddef.h>
+#include <stdint.h>
+#include <string.h>
+
+#define COROUTINE __attribute__((noreturn)) void
+
+enum {COROUTINE_REGISTERS = 0xd0 / 8};
+
+struct coroutine_context
+{
+    void **stack_pointer;
+};
+
+typedef COROUTINE(* coroutine_start)(struct coroutine_context *from, struct coroutine_context *self);
+
+static inline void coroutine_initialize_main(struct coroutine_context * context) {
+    context->stack_pointer = NULL;
+}
+
+static inline void coroutine_initialize(
+    struct coroutine_context *context,
+    coroutine_start start,
+    void *stack,
+    size_t size
+) {
+    assert(start && stack && size >= 1024);
+
+    // Stack grows down. Force 16-byte alignment.
+    char * top = (char*)stack + size;
+    context->stack_pointer = (void**)((uintptr_t)top & ~0xF);
+
+    context->stack_pointer -= COROUTINE_REGISTERS;
+    memset(context->stack_pointer, 0, sizeof(void*) * COROUTINE_REGISTERS);
+
+    context->stack_pointer[0xc0 / 8] = (void*)start;
+}
+
+struct coroutine_context * coroutine_transfer(struct coroutine_context * current, struct coroutine_context * target);
+
+static inline void coroutine_destroy(struct coroutine_context * context)
+{
+}
-- 
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