feat: add support for aarch64 timer/interrupts, port MontaukOS userspace

programs/include/gui/framebuffer.hpp

@@ -13,6 +13,18 @@
 
 namespace gui {
 
+// Drain write-combining stores to the scanout buffer before it is flipped
+// or composited by someone else.
+inline void wc_store_fence() {
+#if defined(__x86_64__)
+    asm volatile("sfence" ::: "memory");
+#elif defined(__aarch64__)
+    asm volatile("dsb st" ::: "memory");
+#else
+#error "unsupported architecture"
+#endif
+}
+
 class Framebuffer {
     uint32_t* hw_fb;
     uint32_t* hw_fb2;    // second scanout buffer (page flip), nullptr if unsupported
@@ -322,12 +334,12 @@ public:
                 montauk::memcpy(mirror, src, row_bytes);
             }
         }
-        if (hw_mirror) asm volatile("sfence" ::: "memory");
+        if (hw_mirror) wc_store_fence();
 
         if (hw_fb2) {
             // Wait for the latch (vsync): the buffer we just left becomes
             // safe to draw into only once the new one is actually scanning.
-            asm volatile("sfence" ::: "memory");
+            wc_store_fence();
             int64_t presented = montauk::fb_flip(hw_next, 1);
             if (presented == hw_next) {
                 hw_next ^= 1;
@@ -359,7 +371,7 @@ public:
                         montauk::memcpy(mirror, src, row_bytes);
                     }
                 }
-                asm volatile("sfence" ::: "memory");
+                wc_store_fence();
             }
         }
     }