[WIP] Support virtio-console

Makefile

@@ -215,6 +215,37 @@ ifeq ($(call has, VIRTIOGPU), 1)
     OBJS_EXTRA += vgpu-display.o
 endif
 
+# console
+SEMU_CONSOLE ?= both
+SEMU_CONSOLE := $(strip $(SEMU_CONSOLE))
+override ENABLE_VIRTIOCONSOLE := 0
+override ENABLE_UART8250 := 0
+ifeq ($(SEMU_CONSOLE),virtio)
+    override ENABLE_VIRTIOCONSOLE := 1
+else ifeq ($(SEMU_CONSOLE),both)
+    override ENABLE_VIRTIOCONSOLE := 1
+    override ENABLE_UART8250 := 1
+else ifeq ($(SEMU_CONSOLE),uart8250)
+    override ENABLE_UART8250 := 1
+else ifeq ($(SEMU_CONSOLE),uart)
+    override ENABLE_UART8250 := 1
+else
+    $(error SEMU_CONSOLE must be virtio, uart8250, or both)
+endif
+
+$(call set-feature, VIRTIOCONSOLE)
+$(call set-feature, UART8250)
+
+ifeq ($(call has, VIRTIOCONSOLE), 1)
+    OBJS_EXTRA += virtio-console.o
+    VIRTIO_CONSOLE_PATH ?= /tmp/semu-hvc0
+    OPTS += --virtio-console-path $(VIRTIO_CONSOLE_PATH)
+endif
+
+ifeq ($(call has, UART8250), 1)
+    OBJS_EXTRA += uart.o
+endif
+
 ifneq ($(filter 1,$(call has, VIRTIOGPU) $(call has, VIRTIOINPUT)),)
     OBJS_EXTRA += window-sw.o
 endif
@@ -227,7 +258,6 @@ OBJS := \
 	ram.o \
 	utils.o \
 	plic.o \
-	uart.o \
 	main.o \
 	aclint.o \
 	coro.o \

README.md

@@ -6,11 +6,12 @@ A minimalist RISC-V system emulator capable of running Linux the kernel and corr
 - Privilege levels: S and U modes
 - Control and status registers (CSR)
 - Virtual memory system: RV32 MMU
-- UART: 8250/16550
+- UART: 8250/16550 console
 - PLIC (platform-level interrupt controller): 32 interrupts, no priority
 - Standard SBI, with the timer extension
 - I/O support using VirtIO standard:
     - virtio-blk acquires disk image from the host.
+    - virtio-console exposes an additional guest console as `/dev/hvc0`.
     - virtio-net is mapped as TAP interface.
     - virtio-snd uses [PortAudio](https://github.com/PortAudio/portaudio) for sound playback on the host with one limitations:
         - As some unknown issues in guest Linux OS (confirmed in v6.7 and v6.12), you need
@@ -67,7 +68,7 @@ With the default external-root build, `make check` uses `Image`, `minimal.dtb`,
 and `ext4.img`, and boots `semu` headlessly with an equivalent command line:
 
 ```shell
-$ ./semu -k Image -c 1 -b minimal.dtb -H -d ext4.img
+$ ./semu -k Image -c 1 -b minimal.dtb -H -d ext4.img --virtio-console-path /tmp/semu-hvc0
 ```
 
 If `ENABLE_EXTERNAL_ROOT=0` is used, `make check` switches to the legacy
@@ -90,6 +91,33 @@ Enter `root` to access shell.
 
 You can exit the emulator using: \<Ctrl-a x\>. (press Ctrl+A, leave it, afterwards press X)
 
+By default, `make check` enables both the 8250 UART console and
+virtio-console. The UART is the primary console, so boot logs and the main
+login prompt appear in the terminal that ran `make check`. The virtio-console
+device is also exposed to the guest as `/dev/hvc0`, and `make check` creates a
+host endpoint at `/tmp/semu-hvc0`.
+
+Open another host terminal to attach to the virtio-console:
+
+```shell
+$ screen /tmp/semu-hvc0
+```
+
+Inside the guest, confirm both consoles are active with:
+
+```shell
+# cat /proc/consoles
+# grep hvc0 /etc/inittab
+```
+
+To use only one console implementation at build time, override
+`SEMU_CONSOLE`:
+
+```shell
+$ make check SEMU_CONSOLE=uart8250
+$ make check SEMU_CONSOLE=virtio
+```
+
 To test virtio-gpu with a visible SDL window, run `semu` manually without `-H`.
 Make sure `sdl2-config` is in `PATH`, then build the emulator, DTB, kernel, and
 test tools disk. Press `Ctrl+Alt+G` to release the mouse cursor from the SDL
@@ -119,7 +147,7 @@ project and can be listed in the guest with:
 ## Usage
 
 ```shell
-./semu -k linux-image [-b dtb-file] [-d disk-image] [-i initrd-image] [-s shared-directory] [-H]
+./semu -k linux-image [-b dtb-file] [-d disk-image] [-i initrd-image] [-s shared-directory] [-H] [--virtio-console-path path]
 ```
 
 * `linux-image` is the path to the Linux kernel `Image`.
@@ -129,6 +157,9 @@ project and can be listed in the guest with:
   from `rootfs.cpio` via `scripts/rootfs_ext4.sh`.
 * `shared-directory` is optional, as it specifies the path of a directory on the host that will be shared with the guest operating system through virtio-fs, enabling file access from the guest via a virtual filesystem mount.
 * `-H` (or `--headless`) skips SDL window creation; useful for CI and `make check`.
+* `virtio-console-path` is optional, as it creates a host-side symlink to the
+  pseudo-terminal connected to the guest `/dev/hvc0`. The default used by
+  `make check` is `/tmp/semu-hvc0`.
 * `initrd-image` is optional and only used on the *legacy* boot path.
   The default `minimal.dtb` built with `ENABLE_EXTERNAL_ROOT=1` does not
   advertise initrd placement, so `-i` there requires either

configs/buildroot.config

@@ -47,4 +47,5 @@ BR2_TARGET_ROOTFS_CPIO_FULL=y
 # BR2_TARGET_ROOTFS_CPIO_DRACUT is not set
 BR2_TARGET_ROOTFS_CPIO_NONE=y
 # BR2_TARGET_ROOTFS_TAR is not set
+BR2_ROOTFS_POST_BUILD_SCRIPT="../target/post-build.sh"
 BR2_PACKAGE_BUSYBOX_CONFIG="busybox.config"

configs/linux.config

@@ -834,7 +834,7 @@ CONFIG_SERIAL_CORE_CONSOLE=y
 # CONFIG_NULL_TTY is not set
 # CONFIG_SERIAL_DEV_BUS is not set
 # CONFIG_TTY_PRINTK is not set
-# CONFIG_VIRTIO_CONSOLE is not set
+CONFIG_VIRTIO_CONSOLE=y
 # CONFIG_IPMI_HANDLER is not set
 CONFIG_HW_RANDOM=y
 CONFIG_HW_RANDOM_VIRTIO=y

device.h

@@ -50,6 +50,8 @@ void plic_write(hart_t *core,
                 uint32_t value);
 /* UART */
 
+#if SEMU_HAS(UART8250)
+
 #define IRQ_UART 1
 #define IRQ_UART_BIT (1 << IRQ_UART)
 
@@ -85,6 +87,7 @@ void u8250_write(hart_t *core,
 void u8250_check_ready(u8250_state_t *uart);
 void u8250_flush_out(u8250_state_t *uart);
 void capture_keyboard_input();
+#endif /* SEMU_HAS(UART8250) */
 
 /* virtio-net */
 
@@ -347,6 +350,54 @@ uint32_t virtio_gpu_register_scanout(virtio_gpu_state_t *vgpu,
                                      uint32_t height);
 #endif /* SEMU_HAS(VIRTIOGPU) */
 
+/* VirtIO-Console */
+
+#if SEMU_HAS(VIRTIOCONSOLE)
+
+#define IRQ_VCONSOLE 10
+#define IRQ_VCONSOLE_BIT (1 << IRQ_VCONSOLE)
+
+typedef struct {
+    uint32_t QueueNum;
+    uint32_t QueueDesc;
+    uint32_t QueueAvail;
+    uint32_t QueueUsed;
+    uint16_t last_avail;
+    bool ready;
+} virtio_console_queue_t;
+
+typedef struct {
+    /* feature negotiation */
+    uint32_t DeviceFeaturesSel;
+    uint32_t DriverFeatures;
+    uint32_t DriverFeaturesSel;
+    /* queue config */
+    uint32_t QueueSel;
+    virtio_console_queue_t queues[2];
+    /* status */
+    uint32_t Status;
+    uint32_t InterruptStatus;
+    /* supplied by environment */
+    uint32_t *ram;
+    int in_fd;
+    int out_fd;
+} virtio_console_state_t;
+
+void virtio_console_read(hart_t *core,
+                         virtio_console_state_t *vcon,
+                         uint32_t addr,
+                         uint8_t width,
+                         uint32_t *value);
+void virtio_console_write(hart_t *core,
+                          virtio_console_state_t *vcon,
+                          uint32_t addr,
+                          uint8_t width,
+                          uint32_t value);
+void virtio_console_init(virtio_console_state_t *vcon);
+void virtio_console_refresh_rx(virtio_console_state_t *vcon);
+
+#endif /* SEMU_HAS(VIRTIOCONSOLE) */
+
 /* ACLINT MTIMER */
 typedef struct {
     /* A MTIMER device has two separate base addresses: one for the MTIME
@@ -558,7 +609,9 @@ typedef struct {
     uint32_t *disk;
     vm_t vm;
     plic_state_t plic;
+#if SEMU_HAS(UART8250)
     u8250_state_t uart;
+#endif
 #if SEMU_HAS(VIRTIONET)
     virtio_net_state_t vnet;
 #endif
@@ -581,6 +634,9 @@ typedef struct {
 #if SEMU_HAS(VIRTIOGPU)
     virtio_gpu_state_t vgpu;
 #endif
+#if SEMU_HAS(VIRTIOCONSOLE)
+    virtio_console_state_t vconsole;
+#endif
 #if SEMU_HAS(VIRTIOINPUT) || SEMU_HAS(VIRTIOGPU)
     /* Use self-pipe trick to unblock the emulator loop when the window backend
      * has queued work, such as input events or window shutdown. When all harts

feature.h

@@ -37,5 +37,15 @@
 #define SEMU_FEATURE_VIRTIOGPU 1
 #endif
 
+/* virtio-console */
+#ifndef SEMU_FEATURE_VIRTIOCONSOLE
+#define SEMU_FEATURE_VIRTIOCONSOLE 1
+#endif
+
+/* 8250/16550 UART console */
+#ifndef SEMU_FEATURE_UART8250
+#define SEMU_FEATURE_UART8250 0
+#endif
+
 /* Feature test macro */
 #define SEMU_HAS(x) SEMU_FEATURE_##x