added riscv64

4 files changed, 133 insertions, 0 deletions

diff --git a/lib/arch/riscv64/README.md b/lib/arch/riscv64/README.md
new file mode 100644
index 0000000..517ddb2
--- /dev/null
+++ b/lib/arch/riscv64/README.md
@@ -0,0 +1,12 @@
+# riscv64 (RISC-V ELF)
+Provide an implementation of the platform specific API as required in
+[`api.h`](../api.h) according to the `RISC-V ELF ABI`.
+
+## Notes: RISC-V ABI
+- Integer/pointer arguments via `x10 - x17`
+- Integer/pointer return values via `x10` - `x11`
+- Callee saved registers `x2`, `x8` - `x9`, `x18` - `x27`, `f8` - `f9`, `f18` - `f27`
+
+## References
+- [RISC-V ABI](https://github.com/riscv/riscv-elf-psabi-doc/blob/master/riscv-elf.md)
+- [RISC-V asm manual](https://github.com/riscv/riscv-asm-manual/blob/master/riscv-asm.md)
diff --git a/lib/arch/riscv64/init_stack.cc b/lib/arch/riscv64/init_stack.cc
new file mode 100644
index 0000000..94dab1c
--- /dev/null
+++ b/lib/arch/riscv64/init_stack.cc
@@ -0,0 +1,39 @@
+/* Copyright (c) 2021 Johannes Stoelp */
+
+#include <cassert>
+#include <cstdint>  // uintN_t
+
+extern "C" void thread_create();
+
+void* init_stack(void* stack_ptr, void (*entry)(void*), const void* ctx) {
+    static_assert(sizeof(uint64_t) == sizeof(std::uintptr_t), "Pointer must be 64bit!");
+
+    // Setup initial stack frame which will be popped when yielding
+    // first time into the thread.
+    // Basic idea is to yield into Thread::entry() function which will
+    // then call the user function.
+
+    uint64_t* stack = static_cast<uint64_t*>(stack_ptr);
+    // Arguments for `thread_create`.
+    *(--stack) = reinterpret_cast<uint64_t>(ctx);
+    *(--stack) = reinterpret_cast<uint64_t>(entry);
+
+    // Yield epilogue.
+    *(--stack) = reinterpret_cast<uint64_t>(thread_create);  // Return address (ra)
+
+    // Callee saved registers.
+    *(--stack) = static_cast<uint64_t>(0);  // x8
+    *(--stack) = static_cast<uint64_t>(0);  // x9
+    *(--stack) = static_cast<uint64_t>(0);  // x18
+    *(--stack) = static_cast<uint64_t>(0);  // x19
+    *(--stack) = static_cast<uint64_t>(0);  // x20
+    *(--stack) = static_cast<uint64_t>(0);  // x21
+    *(--stack) = static_cast<uint64_t>(0);  // x22
+    *(--stack) = static_cast<uint64_t>(0);  // x23
+    *(--stack) = static_cast<uint64_t>(0);  // x24
+    *(--stack) = static_cast<uint64_t>(0);  // x25
+    *(--stack) = static_cast<uint64_t>(0);  // x26
+    *(--stack) = static_cast<uint64_t>(0);  // x27
+
+    return static_cast<void*>(stack);
+}
diff --git a/lib/arch/riscv64/thread_create.s b/lib/arch/riscv64/thread_create.s
new file mode 100644
index 0000000..68c09cd
--- /dev/null
+++ b/lib/arch/riscv64/thread_create.s
@@ -0,0 +1,19 @@
+# Copyright (c) 2021 Johannes Stoelp
+
+    .section .text, "ax", @progbits
+
+     # extern "C" void thread_create();
+    .global thread_create
+    .type   thread_create, @function
+thread_create:
+    .cfi_startproc
+    ld a0, 8(sp)
+    ld x5, 0(sp)
+
+    jalr x5
+
+    # FIXME: no return from thread after user fn finished.
+1:
+    j 1b
+    .cfi_endproc
+    .size thread_create, .-thread_create
diff --git a/lib/arch/riscv64/yield.s b/lib/arch/riscv64/yield.s
new file mode 100644
index 0000000..985cb52
--- /dev/null
+++ b/lib/arch/riscv64/yield.s
@@ -0,0 +1,63 @@
+# Copyright (c) 2021 Johannes Stoelp
+
+    .macro push reg
+        addi sp, sp, -8
+        sd \reg, 0(sp)
+    .endm
+
+    .macro pop reg
+        ld \reg, 0(sp)
+        addi sp, sp, 8
+    .endm
+
+    .section .text, "ax", @progbits
+
+    # extern "C" void yield(const void* new_stack, void** old_stack);
+    #                                   ^^^^^^^^^         ^^^^^^^^^
+    #                                   a0 (x10)          a1 (x11)
+    .global yield
+    .type   yield, @function
+yield:
+    .cfi_startproc
+    # save return address
+    push ra
+
+    # push callee saved registers
+    push x8
+    push x9
+    push x18
+    push x19
+    push x20
+    push x21
+    push x22
+    push x23
+    push x24
+    push x25
+    push x26
+    push x27
+
+    # arg0: a0 holds new stack
+    # arg1: a1 holds addr to location current stack must be saved
+    sd sp, 0(a1)  # save current stack ptr
+    mv sp, a0     # switch to new stack ptr
+
+    # pop callee saved registers
+    pop x27
+    pop x26
+    pop x25
+    pop x24
+    pop x23
+    pop x22
+    pop x21
+    pop x20
+    pop x19
+    pop x18
+    pop x9
+    pop x8
+
+    # restore return address
+    pop ra
+
+    ret
+    .cfi_endproc
+    .size yield, .-yield