kbuild: rust: keep Rust objects out of Clang LTO with inline helpersgrafted

Under `CONFIG_LTO_CLANG` + `CONFIG_RUST_INLINE_HELPERS`, one may hit
`objtool` errors such as:

    vmlinux.o: error: objtool: _R..._3Gsp4boot+0xd6a:
    can't find jump dest instruction at .text._R..._3Gsp4boot+0x1dfd

The reason is that in such builds, the Clang invocation that compiles
the combined Rust plus helpers bitcode emits LLVM bitcode (again) --
the final code generation happens in the linker's LTO step, which the
`-mllvm` trap options passed to Clang do not reach.

This, in turn, means that unreachable traps are missing, and the
impossible paths do not merely fallthrough to the next symbol, but past
the end of their own section, since LTO builds place each function in
its own section.

Thus filter `CC_FLAGS_LTO` out of the Clang invocation, so that it always
emits machine code directly, with the traps in place.

Assisted-by: LLM
Cc: Gary Guo <gary@garyguo.net>
Cc: Boqun Feng <boqun@kernel.org>
Cc: Alice Ryhl <aliceryhl@google.com>
Cc: Matthew Maurer <mmaurer@google.com>
Cc: Josh Poimboeuf <jpoimboe@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: stable@vger.kernel.org
Fixes: 3a2486cc1da5 ("kbuild: rust: provide an option to inline C helpers into Rust")
Acked-by: Gary Guo <gary@garyguo.net>
Link: https://patch.msgid.link/20260816133233.197500-2-ojeda@kernel.org
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

1 files changed, 245 insertions, 0 deletions

diff --git a/Documentation/input/uinput.rst b/Documentation/input/uinput.rst
new file mode 100644
index 000000000..30fe80e32
--- /dev/null
+++ b/Documentation/input/uinput.rst
@@ -0,0 +1,245 @@
+=============
+uinput module
+=============
+
+Introduction
+============
+
+uinput is a kernel module that makes it possible to emulate input devices
+from userspace. By writing to /dev/uinput (or /dev/input/uinput) device, a
+process can create a virtual input device with specific capabilities. Once
+this virtual device is created, the process can send events through it,
+that will be delivered to userspace and in-kernel consumers.
+
+Interface
+=========
+
+::
+
+  linux/uinput.h
+
+The uinput header defines ioctls to create, set up, and destroy virtual
+devices.
+
+libevdev
+========
+
+libevdev is a wrapper library for evdev devices that provides interfaces to
+create uinput devices and send events. libevdev is less error-prone than
+accessing uinput directly, and should be considered for new software.
+
+For examples and more information about libevdev:
+https://www.freedesktop.org/software/libevdev/doc/latest/
+
+Examples
+========
+
+Keyboard events
+---------------
+
+This first example shows how to create a new virtual device, and how to
+send a key event. All default imports and error handlers were removed for
+the sake of simplicity.
+
+.. code-block:: c
+
+   #include <linux/uinput.h>
+
+   void emit(int fd, int type, int code, int val)
+   {
+      struct input_event ie;
+
+      ie.type = type;
+      ie.code = code;
+      ie.value = val;
+      /* timestamp values below are ignored */
+      ie.time.tv_sec = 0;
+      ie.time.tv_usec = 0;
+
+      write(fd, &ie, sizeof(ie));
+   }
+
+   int main(void)
+   {
+      struct uinput_setup usetup;
+
+      int fd = open("/dev/uinput", O_WRONLY | O_NONBLOCK);
+
+
+      /*
+       * The ioctls below will enable the device that is about to be
+       * created, to pass key events, in this case the space key.
+       */
+      ioctl(fd, UI_SET_EVBIT, EV_KEY);
+      ioctl(fd, UI_SET_KEYBIT, KEY_SPACE);
+
+      memset(&usetup, 0, sizeof(usetup));
+      usetup.id.bustype = BUS_USB;
+      usetup.id.vendor = 0x1234; /* sample vendor */
+      usetup.id.product = 0x5678; /* sample product */
+      strcpy(usetup.name, "Example device");
+
+      ioctl(fd, UI_DEV_SETUP, &usetup);
+      ioctl(fd, UI_DEV_CREATE);
+
+      /*
+       * On UI_DEV_CREATE the kernel will create the device node for this
+       * device. We are inserting a pause here so that userspace has time
+       * to detect, initialize the new device, and can start listening to
+       * the event, otherwise it will not notice the event we are about
+       * to send. This pause is only needed in our example code!
+       */
+      sleep(1);
+
+      /* Key press, report the event, send key release, and report again */
+      emit(fd, EV_KEY, KEY_SPACE, 1);
+      emit(fd, EV_SYN, SYN_REPORT, 0);
+      emit(fd, EV_KEY, KEY_SPACE, 0);
+      emit(fd, EV_SYN, SYN_REPORT, 0);
+
+      /*
+       * Give userspace some time to read the events before we destroy the
+       * device with UI_DEV_DESTROY.
+       */
+      sleep(1);
+
+      ioctl(fd, UI_DEV_DESTROY);
+      close(fd);
+
+      return 0;
+   }
+
+Mouse movements
+---------------
+
+This example shows how to create a virtual device that behaves like a physical
+mouse.
+
+.. code-block:: c
+
+   #include <linux/uinput.h>
+
+   /* emit function is identical to of the first example */
+
+   int main(void)
+   {
+      struct uinput_setup usetup;
+      int i = 50;
+
+      int fd = open("/dev/uinput", O_WRONLY | O_NONBLOCK);
+
+      /* enable mouse button left and relative events */
+      ioctl(fd, UI_SET_EVBIT, EV_KEY);
+      ioctl(fd, UI_SET_KEYBIT, BTN_LEFT);
+
+      ioctl(fd, UI_SET_EVBIT, EV_REL);
+      ioctl(fd, UI_SET_RELBIT, REL_X);
+      ioctl(fd, UI_SET_RELBIT, REL_Y);
+
+      memset(&usetup, 0, sizeof(usetup));
+      usetup.id.bustype = BUS_USB;
+      usetup.id.vendor = 0x1234; /* sample vendor */
+      usetup.id.product = 0x5678; /* sample product */
+      strcpy(usetup.name, "Example device");
+
+      ioctl(fd, UI_DEV_SETUP, &usetup);
+      ioctl(fd, UI_DEV_CREATE);
+
+      /*
+       * On UI_DEV_CREATE the kernel will create the device node for this
+       * device. We are inserting a pause here so that userspace has time
+       * to detect, initialize the new device, and can start listening to
+       * the event, otherwise it will not notice the event we are about
+       * to send. This pause is only needed in our example code!
+       */
+      sleep(1);
+
+      /* Move the mouse diagonally, 5 units per axis */
+      while (i--) {
+         emit(fd, EV_REL, REL_X, 5);
+         emit(fd, EV_REL, REL_Y, 5);
+         emit(fd, EV_SYN, SYN_REPORT, 0);
+         usleep(15000);
+      }
+
+      /*
+       * Give userspace some time to read the events before we destroy the
+       * device with UI_DEV_DESTROY.
+       */
+      sleep(1);
+
+      ioctl(fd, UI_DEV_DESTROY);
+      close(fd);
+
+      return 0;
+   }
+
+
+uinput old interface
+--------------------
+
+Before uinput version 5, there wasn't a dedicated ioctl to set up a virtual
+device. Programs supporting older versions of uinput interface need to fill
+a uinput_user_dev structure and write it to the uinput file descriptor to
+configure the new uinput device. New code should not use the old interface
+but interact with uinput via ioctl calls, or use libevdev.
+
+.. code-block:: c
+
+   #include <linux/uinput.h>
+
+   /* emit function is identical to of the first example */
+
+   int main(void)
+   {
+      struct uinput_user_dev uud;
+      int version, rc, fd;
+
+      fd = open("/dev/uinput", O_WRONLY | O_NONBLOCK);
+      rc = ioctl(fd, UI_GET_VERSION, &version);
+
+      if (rc == 0 && version >= 5) {
+         /* use UI_DEV_SETUP */
+         return 0;
+      }
+
+      /*
+       * The ioctls below will enable the device that is about to be
+       * created, to pass key events, in this case the space key.
+       */
+      ioctl(fd, UI_SET_EVBIT, EV_KEY);
+      ioctl(fd, UI_SET_KEYBIT, KEY_SPACE);
+
+      memset(&uud, 0, sizeof(uud));
+      snprintf(uud.name, UINPUT_MAX_NAME_SIZE, "uinput old interface");
+      write(fd, &uud, sizeof(uud));
+
+      ioctl(fd, UI_DEV_CREATE);
+
+      /*
+       * On UI_DEV_CREATE the kernel will create the device node for this
+       * device. We are inserting a pause here so that userspace has time
+       * to detect, initialize the new device, and can start listening to
+       * the event, otherwise it will not notice the event we are about
+       * to send. This pause is only needed in our example code!
+       */
+      sleep(1);
+
+      /* Key press, report the event, send key release, and report again */
+      emit(fd, EV_KEY, KEY_SPACE, 1);
+      emit(fd, EV_SYN, SYN_REPORT, 0);
+      emit(fd, EV_KEY, KEY_SPACE, 0);
+      emit(fd, EV_SYN, SYN_REPORT, 0);
+
+      /*
+       * Give userspace some time to read the events before we destroy the
+       * device with UI_DEV_DESTROY.
+       */
+      sleep(1);
+
+      ioctl(fd, UI_DEV_DESTROY);
+
+      close(fd);
+      return 0;
+   }
+