tracing: add semihosting backend

Using semihosting on supported architectures (arm, xtensa, riscv) it now
possible to generate tracing giles easily and without being restricted
by size.
Using qemu for example, it is now possible to generate the tracing file
simply by running:

 west build -p -b mps2/an385 tests/kernel/msgq/msgq_api/ \
 	-t run --snippet semihost-tracing

This will generate a tracing file in the build/ directory which can be
viewed with babeltrace.

Signed-off-by: Anas Nashif <[email protected]>

Author: nashif

subsys/tracing/CMakeLists.txt

@@ -22,6 +22,11 @@ zephyr_sources_ifdef(
   tracing_backend_usb.c
   )
 
+zephyr_sources_ifdef(
+  CONFIG_TRACING_BACKEND_SEMIHOST
+  tracing_backend_semihosting.c
+  )
+
 zephyr_sources_ifdef(
   CONFIG_TRACING_BACKEND_UART
   tracing_backend_uart.c

subsys/tracing/Kconfig

@@ -159,6 +159,13 @@ config TRACING_BACKEND_RAM
 	  be dumped to a file at runtime with a debugger.
 	  See gdb dump binary memory documentation for example.
 
+config TRACING_BACKEND_SEMIHOST
+	bool "Semihost backend"
+	depends on SEMIHOST
+	help
+	  Use semihosting to output tracing data. This is useful
+	  for debugging on a host machine, such as when using QEMU.
+
 config TRACING_BACKEND_ADSP_MEMORY_WINDOW
 	bool "Memory window in RAM"
 	depends on SOC_FAMILY_INTEL_ADSP
@@ -174,6 +181,7 @@ config TRACING_BACKEND_NAME
 	default "tracing_backend_usb" if TRACING_BACKEND_USB
 	default "tracing_backend_posix" if TRACING_BACKEND_POSIX
 	default "tracing_backend_ram" if TRACING_BACKEND_RAM
+	default "tracing_backend_semihost" if TRACING_BACKEND_SEMIHOST
 	default "tracing_backend_adsp_memory_window" if TRACING_BACKEND_ADSP_MEMORY_WINDOW
 
 config RAM_TRACING_BUFFER_SIZE

subsys/tracing/tracing_backend_semihosting.c

@@ -0,0 +1,37 @@
+/*
+ * Copyright (c) 2021 IoT.bzh
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#include <ctype.h>
+#include <zephyr/kernel.h>
+#include <tracing_core.h>
+#include <tracing_backend.h>
+#include <zephyr/arch/common/semihost.h>
+
+static int tracing_fd = -1;
+
+static void tracing_backend_semihost_output(
+		const struct tracing_backend *backend,
+		uint8_t *data, uint32_t length)
+{
+	semihost_write(tracing_fd, data, length);
+}
+
+static void tracing_backend_semihost_init(void)
+{
+	const char *tracing_file = "./tracing.bin";
+	tracing_fd = semihost_open(tracing_file, SEMIHOST_OPEN_AB_PLUS);
+    __ASSERT(tracing_fd >= 0, "semihost_open() returned %d", tracing_fd);
+    if (tracing_fd < 0) {
+		k_panic();
+    }
+}
+
+const struct tracing_backend_api tracing_backend_semihost_api = {
+	.init = tracing_backend_semihost_init,
+	.output  = tracing_backend_semihost_output
+};
+
+TRACING_BACKEND_DEFINE(tracing_backend_semihost, tracing_backend_semihost_api);