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rust-raspberrypi-OS-tutorials/03_hacky_hello_world/README.ES.md

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Tutorial 03 - Hacky Hello World

tl;dr

  • Se añade la macro global print!() para habilitar la "depuración basada en printf" ("printf debugging") lo más pronto posible.
  • Para mantener una duración razonable en este tutorial, las funciones de impresión por el momento "abusan" una propiedad de QEMU que nos permite hacer uso del UART de la Raspberry sin haberla configurado apropiadamente.
  • El uso del hardware real de UART se habilitará paso por paso en los siguientes tutoriales.

Adiciones notables

  • src/console.rs introduce una interfaz con Traits para comandos de consola.
  • src/bsp/raspberrypi/console.rs implementa la interfaz para que QEMU pueda crear una emulación de UART.
  • El panic handler (manejador de pánico) hace uso de la nueva macro print!() para mostrar mensajes de error del usuario.
  • Hay un nuevo objetivo en el Makefile: make test, destinado a la automatización de pruebas. Este comando inicia el kernel (núcleo) compilado en QEMU, y busca una cadena de texto específica en la salida que ha sido producida por el kernel (núcleo).
    • En este tutorial, se buscará la cadena Stopping here, que es creada por la macro panic!() al final del archivo main.rs.

Pruébalo

QEMU ya no está siendo ejecutado en modo ensamblador. Desde ahora en adelante mostrará la salida de la consola.

$ make qemu
[...]
Hello from Rust!

Kernel panic: Stopping here.

Diccionario

  • Hacky: Solución torpe o poco elegante para un problema.

  • Debugging: Proceso para identificar y corregir errores de programación.

    • printf debugging: Usado para describir el trabajo de depuración (debugging) poniendo comandos que dan una salida en consola, como el de "printf", en diferentes lugares del programa; observando la información y tratando de deducir qué está mal en el programa basándose en la información que nos dan nuestros comandos.

  • Traits: Un trait le hace saber al compilador de Rust acerca de una funcionalidad que tiene un tipo de dato particular y que puede compartir con otros tipos de datos.

    NOTA: Los traits son similares a una característica que se le conoce comúnmente como interfaces en otros lenguajes, aunque con algunas diferencias.

    Si deseas aprender más acerca de esto, por favor lee este capítulo del libro de Rust: Traits: Defining Shared Behavior - The Rust Programming Language

Diferencias con el archivo anterior

diff -uNr 02_runtime_init/Cargo.toml 03_hacky_hello_world/Cargo.toml
--- 02_runtime_init/Cargo.toml
+++ 03_hacky_hello_world/Cargo.toml
@@ -1,6 +1,6 @@
 [package]
 name = "mingo"
-version = "0.2.0"
+version = "0.3.0"
 authors = ["Andre Richter <andre.o.richter@gmail.com>"]
 edition = "2021"


diff -uNr 02_runtime_init/Makefile 03_hacky_hello_world/Makefile
--- 02_runtime_init/Makefile
+++ 03_hacky_hello_world/Makefile
@@ -24,7 +24,7 @@
     KERNEL_BIN        = kernel8.img
     QEMU_BINARY       = qemu-system-aarch64
     QEMU_MACHINE_TYPE = raspi3
-    QEMU_RELEASE_ARGS = -d in_asm -display none
+    QEMU_RELEASE_ARGS = -serial stdio -display none
     OBJDUMP_BINARY    = aarch64-none-elf-objdump
     NM_BINARY         = aarch64-none-elf-nm
     READELF_BINARY    = aarch64-none-elf-readelf
@@ -35,7 +35,7 @@
     KERNEL_BIN        = kernel8.img
     QEMU_BINARY       = qemu-system-aarch64
     QEMU_MACHINE_TYPE =
-    QEMU_RELEASE_ARGS = -d in_asm -display none
+    QEMU_RELEASE_ARGS = -serial stdio -display none
     OBJDUMP_BINARY    = aarch64-none-elf-objdump
     NM_BINARY         = aarch64-none-elf-nm
     READELF_BINARY    = aarch64-none-elf-readelf
@@ -71,17 +71,20 @@
     --strip-all            \
     -O binary

-EXEC_QEMU = $(QEMU_BINARY) -M $(QEMU_MACHINE_TYPE)
+EXEC_QEMU          = $(QEMU_BINARY) -M $(QEMU_MACHINE_TYPE)
+EXEC_TEST_DISPATCH = ruby ../common/tests/dispatch.rb

 ##------------------------------------------------------------------------------
 ## Dockerization
 ##------------------------------------------------------------------------------
-DOCKER_CMD          = docker run -t --rm -v $(shell pwd):/work/tutorial -w /work/tutorial
-DOCKER_CMD_INTERACT = $(DOCKER_CMD) -i
+DOCKER_CMD            = docker run -t --rm -v $(shell pwd):/work/tutorial -w /work/tutorial
+DOCKER_CMD_INTERACT   = $(DOCKER_CMD) -i
+DOCKER_ARG_DIR_COMMON = -v $(shell pwd)/../common:/work/common

 # DOCKER_IMAGE defined in include file (see top of this file).
 DOCKER_QEMU  = $(DOCKER_CMD_INTERACT) $(DOCKER_IMAGE)
 DOCKER_TOOLS = $(DOCKER_CMD) $(DOCKER_IMAGE)
+DOCKER_TEST  = $(DOCKER_CMD) $(DOCKER_ARG_DIR_COMMON) $(DOCKER_IMAGE)



@@ -169,3 +172,28 @@
 ##------------------------------------------------------------------------------
 check:
     @RUSTFLAGS="$(RUSTFLAGS)" $(CHECK_CMD) --message-format=json
+
+
+
+##--------------------------------------------------------------------------------------------------
+## Testing targets
+##--------------------------------------------------------------------------------------------------
+.PHONY: test test_boot
+
+ifeq ($(QEMU_MACHINE_TYPE),) # QEMU is not supported for the board.
+
+test_boot test :
+    $(call colorecho, "\n$(QEMU_MISSING_STRING)")
+
+else # QEMU is supported.
+
+##------------------------------------------------------------------------------
+## Run boot test
+##------------------------------------------------------------------------------
+test_boot: $(KERNEL_BIN)
+    $(call colorecho, "\nBoot test - $(BSP)")
+    @$(DOCKER_TEST) $(EXEC_TEST_DISPATCH) $(EXEC_QEMU) $(QEMU_RELEASE_ARGS) -kernel $(KERNEL_BIN)
+
+test: test_boot
+
+endif

diff -uNr 02_runtime_init/src/bsp/raspberrypi/console.rs 03_hacky_hello_world/src/bsp/raspberrypi/console.rs
--- 02_runtime_init/src/bsp/raspberrypi/console.rs
+++ 03_hacky_hello_world/src/bsp/raspberrypi/console.rs
@@ -0,0 +1,47 @@
+// SPDX-License-Identifier: MIT OR Apache-2.0
+//
+// Copyright (c) 2018-2022 Andre Richter <andre.o.richter@gmail.com>
+
+//! BSP console facilities.
+
+use crate::console;
+use core::fmt;
+
+//--------------------------------------------------------------------------------------------------
+// Private Definitions
+//--------------------------------------------------------------------------------------------------
+
+/// A mystical, magical device for generating QEMU output out of the void.
+struct QEMUOutput;
+
+//--------------------------------------------------------------------------------------------------
+// Private Code
+//--------------------------------------------------------------------------------------------------
+
+/// Implementing `core::fmt::Write` enables usage of the `format_args!` macros, which in turn are
+/// used to implement the `kernel`'s `print!` and `println!` macros. By implementing `write_str()`,
+/// we get `write_fmt()` automatically.
+///
+/// See [`src/print.rs`].
+///
+/// [`src/print.rs`]: ../../print/index.html
+impl fmt::Write for QEMUOutput {
+    fn write_str(&mut self, s: &str) -> fmt::Result {
+        for c in s.chars() {
+            unsafe {
+                core::ptr::write_volatile(0x3F20_1000 as *mut u8, c as u8);
+            }
+        }
+
+        Ok(())
+    }
+}
+
+//--------------------------------------------------------------------------------------------------
+// Public Code
+//--------------------------------------------------------------------------------------------------
+
+/// Return a reference to the console.
+pub fn console() -> impl console::interface::Write {
+    QEMUOutput {}
+}

diff -uNr 02_runtime_init/src/bsp/raspberrypi.rs 03_hacky_hello_world/src/bsp/raspberrypi.rs
--- 02_runtime_init/src/bsp/raspberrypi.rs
+++ 03_hacky_hello_world/src/bsp/raspberrypi.rs
@@ -4,4 +4,5 @@

 //! Top-level BSP file for the Raspberry Pi 3 and 4.

+pub mod console;
 pub mod cpu;

diff -uNr 02_runtime_init/src/console.rs 03_hacky_hello_world/src/console.rs
--- 02_runtime_init/src/console.rs
+++ 03_hacky_hello_world/src/console.rs
@@ -0,0 +1,19 @@
+// SPDX-License-Identifier: MIT OR Apache-2.0
+//
+// Copyright (c) 2018-2022 Andre Richter <andre.o.richter@gmail.com>
+
+//! System console.
+
+//--------------------------------------------------------------------------------------------------
+// Public Definitions
+//--------------------------------------------------------------------------------------------------
+
+/// Console interfaces.
+pub mod interface {
+    /// Console write functions.
+    ///
+    /// `core::fmt::Write` is exactly what we need for now. Re-export it here because
+    /// implementing `console::Write` gives a better hint to the reader about the
+    /// intention.
+    pub use core::fmt::Write;
+}

diff -uNr 02_runtime_init/src/main.rs 03_hacky_hello_world/src/main.rs
--- 02_runtime_init/src/main.rs
+++ 03_hacky_hello_world/src/main.rs
@@ -104,12 +104,16 @@
 //!     - It is implemented in `src/_arch/__arch_name__/cpu/boot.s`.
 //! 2. Once finished with architectural setup, the arch code calls `kernel_init()`.

+#![feature(format_args_nl)]
+#![feature(panic_info_message)]
 #![no_main]
 #![no_std]

 mod bsp;
+mod console;
 mod cpu;
 mod panic_wait;
+mod print;

 /// Early init code.
 ///
@@ -117,5 +121,7 @@
 ///
 /// - Only a single core must be active and running this function.
 unsafe fn kernel_init() -> ! {
-    panic!()
+    println!("[0] Hello from Rust!");
+
+    panic!("Stopping here.")
 }

diff -uNr 02_runtime_init/src/panic_wait.rs 03_hacky_hello_world/src/panic_wait.rs
--- 02_runtime_init/src/panic_wait.rs
+++ 03_hacky_hello_world/src/panic_wait.rs
@@ -4,10 +4,16 @@

 //! A panic handler that infinitely waits.

-use crate::cpu;
+use crate::{cpu, println};
 use core::panic::PanicInfo;

 #[panic_handler]
-fn panic(_info: &PanicInfo) -> ! {
+fn panic(info: &PanicInfo) -> ! {
+    if let Some(args) = info.message() {
+        println!("\nKernel panic: {}", args);
+    } else {
+        println!("\nKernel panic!");
+    }
+
     cpu::wait_forever()
 }

diff -uNr 02_runtime_init/src/print.rs 03_hacky_hello_world/src/print.rs
--- 02_runtime_init/src/print.rs
+++ 03_hacky_hello_world/src/print.rs
@@ -0,0 +1,38 @@
+// SPDX-License-Identifier: MIT OR Apache-2.0
+//
+// Copyright (c) 2018-2022 Andre Richter <andre.o.richter@gmail.com>
+
+//! Printing.
+
+use crate::{bsp, console};
+use core::fmt;
+
+//--------------------------------------------------------------------------------------------------
+// Public Code
+//--------------------------------------------------------------------------------------------------
+
+#[doc(hidden)]
+pub fn _print(args: fmt::Arguments) {
+    use console::interface::Write;
+
+    bsp::console::console().write_fmt(args).unwrap();
+}
+
+/// Prints without a newline.
+///
+/// Carbon copy from <https://doc.rust-lang.org/src/std/macros.rs.html>
+#[macro_export]
+macro_rules! print {
+    ($($arg:tt)*) => ($crate::print::_print(format_args!($($arg)*)));
+}
+
+/// Prints with a newline.
+///
+/// Carbon copy from <https://doc.rust-lang.org/src/std/macros.rs.html>
+#[macro_export]
+macro_rules! println {
+    () => ($crate::print!("\n"));
+    ($($arg:tt)*) => ({
+        $crate::print::_print(format_args_nl!($($arg)*));
+    })
+}

diff -uNr 02_runtime_init/tests/boot_test_string.rb 03_hacky_hello_world/tests/boot_test_string.rb
--- 02_runtime_init/tests/boot_test_string.rb
+++ 03_hacky_hello_world/tests/boot_test_string.rb
@@ -0,0 +1,3 @@
+# frozen_string_literal: true
+
+EXPECTED_PRINT = 'Stopping here'