From dfa05a97e083122a788c0ffb5c9e26888fe3dcd1 Mon Sep 17 00:00:00 2001
From: johannst <johannes.stoelp@gmail.com>
Date: Thu, 17 Sep 2020 00:06:28 +0200
Subject: setup new stack + basic yielding between two stacks

---
 lib/matcha.h | 77 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 77 insertions(+)
 create mode 100644 lib/matcha.h

(limited to 'lib/matcha.h')

diff --git a/lib/matcha.h b/lib/matcha.h
new file mode 100644
index 0000000..9387bf9
--- /dev/null
+++ b/lib/matcha.h
@@ -0,0 +1,77 @@
+#include <cassert>
+#include <cstdint>
+#include <cstdio>
+#include <sys/mman.h>
+#include <unistd.h>  // sysconf
+
+extern "C" void thread_create();
+extern "C" void yield(void* new_stack, void** old_stack);
+
+long get_pagesize() {
+    return sysconf(_SC_PAGESIZE);
+}
+
+struct Thread {
+    Thread(const Thread&) = delete;
+    Thread& operator=(const Thread&) = delete;
+    Thread(void (*fn)());
+
+    static void entry(void* obj);
+
+    // private:
+    void* mStackPtr;
+    void (*mUserFn)();
+};
+
+Thread::Thread(void (*fn)()) : mUserFn(fn) {
+    const long PAGE_SIZE = get_pagesize();
+    const long STACK_SIZE = 8 * PAGE_SIZE;
+
+    // create new stack
+    void* stack = mmap(nullptr, STACK_SIZE, PROT_WRITE | PROT_READ, MAP_PRIVATE | MAP_ANONYMOUS, -1 /* fd */, 0 /* offset */);
+    assert(stack != MAP_FAILED);
+
+    // protect last stack page (lowest addr)
+    int ret = mprotect(stack, PAGE_SIZE, PROT_NONE);
+    assert(ret == 0);
+
+    // stack grows downwards
+    mStackPtr = static_cast<uint8_t*>(stack) + STACK_SIZE;
+    {
+        uint64_t* stack = static_cast<uint64_t*>(mStackPtr);
+        *(--stack) = (uint64_t)this;
+        *(--stack) = (uint64_t)Thread::entry;
+
+        // initial values for yield epilog
+        *(--stack) = (uint64_t)thread_create;
+        *(--stack) = (uint64_t)0;
+
+        // initial values for callee saved regs
+        *(--stack) = (uint64_t)0;                                        // rbx
+        *(--stack) = (uint64_t)(static_cast<uint64_t*>(mStackPtr) - 4);  // rbp
+        *(--stack) = (uint64_t)0;                                        // r12
+        *(--stack) = (uint64_t)0;                                        // r13
+        *(--stack) = (uint64_t)0;                                        // r14
+        *(--stack) = (uint64_t)0;                                        // r15
+
+        mStackPtr = static_cast<void*>(stack);
+    }
+}
+
+void Thread::entry(void* obj) {
+    Thread* t = static_cast<Thread*>(obj);
+
+    puts("thread entry");
+    t->mUserFn();
+    puts("thread done");
+}
+
+void* gOriginalStack;
+
+void yield_to(const Thread& t) {
+    yield(t.mStackPtr, &gOriginalStack);
+}
+
+void yield_from(Thread& t) {
+    yield(gOriginalStack, &t.mStackPtr);
+}
-- 
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