From 0d881bc974b74dff75c00a3cab5d535cbb2ace46 Mon Sep 17 00:00:00 2001
From: johannst <johannes.stoelp@gmail.com>
Date: Fri, 26 Feb 2021 23:19:03 +0100
Subject: added implementation for armv7a

---
 lib/arch/arm/README.md       |  9 +++++++++
 lib/arch/arm/api.h           |  6 ++++++
 lib/arch/arm/init_stack.cc   | 35 +++++++++++++++++++++++++++++++++++
 lib/arch/arm/thread_create.s | 20 ++++++++++++++++++++
 lib/arch/arm/yield.s         | 32 ++++++++++++++++++++++++++++++++
 5 files changed, 102 insertions(+)
 create mode 100644 lib/arch/arm/README.md
 create mode 100644 lib/arch/arm/api.h
 create mode 100644 lib/arch/arm/init_stack.cc
 create mode 100644 lib/arch/arm/thread_create.s
 create mode 100644 lib/arch/arm/yield.s

(limited to 'lib/arch/arm')

diff --git a/lib/arch/arm/README.md b/lib/arch/arm/README.md
new file mode 100644
index 0000000..8631c93
--- /dev/null
+++ b/lib/arch/arm/README.md
@@ -0,0 +1,9 @@
+# Procedure Call Standard ARM64
+
+- Integer/pointer arguments via `r0`-`r3`
+- Integer/pointer return values via `r0`
+- Callee saved registers `r4`-`r11`, `sp`, `lr`, `fp`
+
+## Reference
+- [johannst armv7 notes](https://johannst.github.io/notes/arch/armv7.html)
+
diff --git a/lib/arch/arm/api.h b/lib/arch/arm/api.h
new file mode 100644
index 0000000..c7a688d
--- /dev/null
+++ b/lib/arch/arm/api.h
@@ -0,0 +1,6 @@
+/* Copyright (c) 2021 Johannes Stoelp */
+
+#pragma once
+
+extern "C" void yield(const void* new_stack, void** old_stack);
+void* init_stack(void* stack_ptr, void (*entry)(void*), const void* ctx);
diff --git a/lib/arch/arm/init_stack.cc b/lib/arch/arm/init_stack.cc
new file mode 100644
index 0000000..422be64
--- /dev/null
+++ b/lib/arch/arm/init_stack.cc
@@ -0,0 +1,35 @@
+#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(uint32_t) == sizeof(std::uintptr_t), "Pointer must be 32bit!");
+
+    // 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.
+
+    uint32_t* stack = static_cast<uint32_t*>(stack_ptr);
+    // Arguments for `thread_create`.
+    *(--stack) = reinterpret_cast<uint32_t>(ctx);
+    *(--stack) = reinterpret_cast<uint32_t>(entry);
+
+    // Yield epilogue.
+    *(--stack) = reinterpret_cast<uint32_t>(thread_create);  // r15 (PC)
+    *(--stack) = static_cast<uint32_t>(0);                   // r11 (FP)
+
+    // Callee saved registers.
+    *(--stack) = static_cast<uint32_t>(0);  // r11
+    *(--stack) = static_cast<uint32_t>(0);  // r10
+    *(--stack) = static_cast<uint32_t>(0);  // r9
+    *(--stack) = static_cast<uint32_t>(0);  // r8
+    *(--stack) = static_cast<uint32_t>(0);  // r7
+    *(--stack) = static_cast<uint32_t>(0);  // r6
+    *(--stack) = static_cast<uint32_t>(0);  // r5
+    *(--stack) = static_cast<uint32_t>(0);  // r4
+
+    assert((reinterpret_cast<std::uintptr_t>(stack) & 0x7) == 0);  // 8byte aligned
+    return static_cast<void*>(stack);
+}
diff --git a/lib/arch/arm/thread_create.s b/lib/arch/arm/thread_create.s
new file mode 100644
index 0000000..7231c3e
--- /dev/null
+++ b/lib/arch/arm/thread_create.s
@@ -0,0 +1,20 @@
+# Copyright (c) 2021 Johannes Stoelp
+
+    .arch armv7-a
+    .section .text, "ax", %progbits
+
+     # extern "C" void thread_create();
+    .global thread_create
+    .type   thread_create, %function
+thread_create:
+    .cfi_startproc
+    ldr r0, [sp, #0x4]
+    ldr r1, [sp]
+
+    blx r1
+
+    # FIXME: no return from thread after user fn finished.
+1:
+    b 1b
+    .cfi_endproc
+    .size thread_create, .-thread_create
diff --git a/lib/arch/arm/yield.s b/lib/arch/arm/yield.s
new file mode 100644
index 0000000..de9d604
--- /dev/null
+++ b/lib/arch/arm/yield.s
@@ -0,0 +1,32 @@
+# Copyright (c) 2021 Johannes Stoelp
+
+    .arch armv7-a
+    .section .text, "ax", %progbits
+
+    # extern "C" void yield(const void* new_stack, void** old_stack);
+    #                                   ^^^^^^^^^         ^^^^^^^^^
+    #                                   x0                x1
+    .global yield
+    .type   yield, %function
+yield:
+    .cfi_startproc
+    // prologue
+    push {fp, lr}
+    mov fp, sp
+
+    // push callee saved registers
+    push {r4-r11}
+
+    // arg0: r0 holds new stack
+    // arg1: r1 holds addr to location current stack must be saved
+    mov r2, sp
+    str r2, [r1]  // save current stack ptr
+    mov sp, r0    // switch to new stack ptr
+
+    // pop callee saved registers
+    pop {r4-r11}
+
+    // epilogue
+    pop {fp, pc}
+    .cfi_endproc
+    .size yield, .-yield
-- 
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