Add a libc skeleton with a primitive malloc.

lib/libc/src/malloc.cpp

@@ -0,0 +1,44 @@
+#include <zcall.h>
+
+#include "stdlib.h"
+
+namespace {
+class NaiveAllocator {
+ public:
+  constexpr static uint64_t kSize = 0x4000;
+  NaiveAllocator() {}
+  bool is_init() { return next_addr_ != 0; }
+  void Init() {
+    uint64_t vmmo_cap;
+    uint64_t err = ZMemoryObjectCreate(kSize, &vmmo_cap);
+    if (err != 0) {
+      ZProcessExit(err);
+    }
+    err = ZAddressSpaceMap(Z_INIT_VMAS_SELF, 0, vmmo_cap, &next_addr_);
+    max_addr_ = next_addr_ + kSize;
+  }
+
+  void* Allocate(size_t size) {
+    uint64_t addr = next_addr_;
+    next_addr_ += size;
+    if (next_addr_ >= max_addr_) {
+      return 0;
+    }
+    return reinterpret_cast<void*>(addr);
+  }
+
+ private:
+  uint64_t next_addr_ = 0;
+  uint64_t max_addr_ = 0;
+};
+
+NaiveAllocator gAlloc;
+
+}  // namespace
+
+void* malloc(size_t size) {
+  if (!gAlloc.is_init()) {
+    gAlloc.Init();
+  }
+  return gAlloc.Allocate(size);
+}