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Magenta.md

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Overview

Magenta is the base operating system, including the kernel and device drivers and support infrastructure.

Magenta is written in a subset of modern C++ [https://github.com/fuchsia-mirror/magenta/blob/master/docs/cxx.md], with C (25%) and asm (3%). It is based on a microkernel, which supports capabilities, message passing and limited device support (mostly for supporting low-level bus operations). Device drivers and filesystems are written as processes using a DDK interface.

Infrastructure

  • stuff for loading drivers
  • filesystem to contain drivers
  • library to access syscalls
  • library support for misc stuff like executing procs
  • "misc" drivers for providing environment support, like "root handle"

Security

  • there are no users. only capabilities.
  • capabilities, based on kernel object handles and rights. Each handle is associated with rights that say how the handle may be used.
  • object handles are owned by a single process and their handles are not valid in any other processes.
  • multiple object handles may reference the same object
  • object handles can be transfered to other processes via message passing. while in transit they are not owned by the sender or the receiver, but are owned by the kernel.
  • kernel has policy settings for limiting operations. XXX investigate more XXX QueryPolicy
  • handles have weak obfuscation. each process has a random mask that handles are xor'd against.

Drivers and DDK

Kernel Code

  • Handle lib/magenta/include/magenta/handle.h record the owning process, the object (dispatcher) they reference, and the rights associated with the handle.
  • Dispatcher lib/magenta/include/magenta/dispatcher.h is the base class for kernel objects.
  • JobDispatcher ./lib/magenta/include/magenta/job_dispatcher.h is an object representing a job. Jobs group together processes and other jobs.
  • ProcessDispatcher ./lib/magenta/include/magenta/process_dispatcher.h are objects for managing processes. It contains a list of UserThreads, a reference to a VmAspace, a list of Handles. and a reference to a
  • ThreadDispatcher ./lib/magenta/include/magenta/thread_dispatcher.h represents a thread by referencing a UserThread ./lib/magenta/include/magenta/user_thread.h.
  • rights are defined in system/public/magenta/types.h
  • signals are defined in system/public/magenta/types.h
  • important types:
    • mx_koid_t are object IDs

Random Tips

  • see [https://github.com/fuchsia-mirror/magenta/blob/master/docs/hacking.md] for info on getting to the shell window, and using keys. Alt-Esc to switch to terminals, Alt-Fn to jump to terminals, Alt-tab to switch to next terminal.
  • The shell has a few interesting builtins for hacking:
    • k help and `k mx help. Sends messages to a kernel debugging interface. Output goes to serial console. See magenta/third_party/uapp/dash/src/bltin/magenta.c mxc_k() for details See kernel/lib/magenta/diagnostics.cpp cmd_diagnostics() for mx commands.
    • from shell run @? and @ bootstrap launch spinning_square. Sends a message to dmctl, which sends it to the application manager which tries to launch an application. See magenta/third_party/uapp/dash/src/bltin/magenta.c mxc_at() for details See application/src/manager/command_listener.cc
    • from shell run dm help, dm reboot, dm "kerneldebug help (same as k help), dm @? (same as @?) Sends a message directly to dmctl XXX show equivalent command as launching bootstrap? See magenta/third_party/uapp/dash/src/bltin/magenta.c mxc_dm() for details See system/core/devmgr/dmctl.c, related devmgr files for more, and /dev/class/misc/dmctl for more