add initial bootloader work

1 files changed, 40 insertions, 0 deletions

diff --git a/loader_stage2.c b/loader_stage2.c
new file mode 100644
index 0000000..98ce571
--- /dev/null
+++ b/loader_stage2.c
@@ -0,0 +1,40 @@
+#include <stddef.h>
+#include <stdint.h>
+#include <uart.h>
+#include <global.h>
+
+void *const kernel_load_addr = ((void*) 0x8000);
+
+void __attribute__((section(".text.stage2main")))
+stage2(uint32_t r0, uint32_t r1, uint32_t atags)
+{
+  // Declare as unused
+  (void) r0;
+  (void) r1;
+  (void) atags;
+
+  uart_puts("hello stage2!\n\r");
+
+  // get kernel size via uart (little endian)
+  uint32_t b0, b1, b2, b3;
+  
+  b0 = uart_getc();
+  b1 = uart_getc();
+  b2 = uart_getc();
+  b3 = uart_getc();
+  
+  uint32_t kernel_size = b0 | (b1 << 8) | (b2 << 16) | (b3 << 24);
+
+  // load kernel at kernel_load_addr
+  char *dst = kernel_load_addr, *end = dst + kernel_size;
+
+  while (dst < end)
+    *(dst++) = uart_getc();
+
+  // jump to kernel
+  // TODO also forward arguments (r0, r1, atags)
+  asm volatile("bx %0" :: "r" (kernel_load_addr) : "memory");
+}
+
+void *const _start = ((void*) stage2); // for linker script
+