[kernel] Add test mode, controlled by manifest

The manifest can now supply a list of boot flags, including "test".
Those get turned into the bootproto::args::flags field by the
bootloader. The kernel takes those and uses the test flag to control
enabling syscalls with the new "test" attribute, like the new
test_finish syscall, which lets automated tests call back to the kernel
to shut down the system.

src/boot/bootconfig.cpp

@@ -41,7 +41,8 @@ bootconfig::bootconfig(util::buffer data, uefi::boot_services *bs)
     data += 1; // reserved byte
     uint16_t num_programs = *util::read<uint16_t>(data);
     uint16_t num_data = *util::read<uint16_t>(data);
-    data += 2; // reserved short
+
+    m_flags = *util::read<uint16_t>(data);
 
     read_descriptor(m_kernel, data);
     read_descriptor(m_init, data);

src/boot/bootconfig.h

@@ -28,12 +28,14 @@ public:
     /// Constructor. Loads bootconfig from the given buffer.
     bootconfig(util::buffer data, uefi::boot_services *bs);
 
-    inline const descriptor & kernel() { return m_kernel; }
-    inline const descriptor & init() { return m_init; }
+    inline uint16_t flags() const { return m_flags; }
+    inline const descriptor & kernel() const { return m_kernel; }
+    inline const descriptor & init() const { return m_init; }
     descriptors programs() { return m_programs; }
     descriptors data() { return m_data; }
 
 private:
+    uint16_t m_flags;
     descriptor m_kernel;
     descriptor m_init;
     descriptors m_programs;

src/boot/main.cpp

@@ -77,6 +77,7 @@ load_resources(bootproto::args *args, video::screen *screen, uefi::handle image,
 
     args->kernel = loader::load_program(disk, bc.kernel(), true);
     args->init = loader::load_program(disk, bc.init());
+    args->flags = static_cast<bootproto::boot_flags>(bc.flags());
 
     namespace bits = util::bits;
     using bootproto::desc_flags;