Fix debugging in VSCode before kernel is started

README.md

@@ -118,10 +118,3 @@ This will most likely break the usage of other plugins until the backup is resto
 * Other Arm cores than Cortex-M33: This plugin has only been tested initially on nrf9160dk, and no work has been done to verify differences between Arm architectures on Zephyr.
 * Other than Arm cores: Zero effort has been used to other architectures, and the plugin does not even check the core parameter, so it might probably crash or show garbage values.
 * Distributing the built .DLL file in Windows requires user to install [Visual C++ Redistributable](https://support.microsoft.com/en-us/topic/the-latest-supported-visual-c-downloads-2647da03-1eea-4433-9aff-95f26a218cc0) on a target machine.
-
-
-## Known problems in JLinkGDBServer
-
-* When `RTOS_GetNumThreads()` returns zero, GDB server still calls `RTOS_GetThreadRegList()` with thread id zero and generates a new dummy thread for GDB. This breaks debugging of the board startup.
-* There is no easy way to tell GDBServer that CPU is not yet running in Thread mode, and therefore
-  plugin should be ignored.

unittests/plugin_test.c

@@ -6,6 +6,7 @@
  * SPDX-License-Identifier: Apache-2.0
  */
 
+#include <stdbool.h>
 #include <stdio.h>
 #include <stdint.h>
 #include <stddef.h>
@@ -14,6 +15,7 @@
 
 #include "acutest.h"
 
+#define GDB_NO_THREAD   0xDEAD
 
 /*************************
  * Dummy data
@@ -76,17 +78,21 @@ struct stack {
 struct dummy_data {
 	uint32_t padding[1]; // Cannot start from offset zero.
 	struct my_kernel kernel;
+	bool post_kernel;
 	uint32_t debug_offsets[LEN_DEBUG_OFFSETS];
 	struct my_thread thread1;
 	struct my_thread thread2;
 	struct stack stack;
 	uint8_t extra_mem[2048];
-} dummy_data = {
+};
+
+struct dummy_data dummy_data = {
 	.kernel = {
 		.version = 1,
 		.current = offsetof(struct dummy_data, thread1),
 		.threads = offsetof(struct dummy_data, thread1)
 	},
+	.post_kernel = true,
 	.thread1 = {
 		.name = "First Thread",
 		.saved = {.psp = offsetof(struct dummy_data, stack) },
@@ -115,7 +121,33 @@ struct dummy_data {
 	}
 };
 
-uint8_t *mem = (uint8_t *) &dummy_data;
+struct dummy_data boot_dummy_data = {
+	.kernel = {
+		.version = 1,
+		.current = 0,
+		.threads = 0
+	},
+	.post_kernel = false,
+	.stack = {
+		.r0 = 0xdeadbeef,
+		.pc = 0xcafebabe,
+	},
+	.debug_offsets = {
+	offsetof(struct my_kernel, version),
+	offsetof(struct my_kernel, current),
+	offsetof(struct my_kernel, threads),
+	offsetof(struct my_thread, next),
+	offsetof(struct my_thread, next),
+	offsetof(struct my_thread, state),
+	offsetof(struct my_thread, state),
+	offsetof(struct my_thread, priority),
+	offsetof(struct my_thread, saved.psp),
+	offsetof(struct my_thread, name),
+	offsetof(struct my_thread, arch),
+	}
+};
+
+uint8_t *mem;
 
 
 
@@ -265,10 +297,12 @@ void test_init(void)
 	TEST_ASSERT(symbols != NULL);
 	symbols[0].address = offsetof(struct dummy_data, kernel);
 	symbols[1].address = offsetof(struct dummy_data, debug_offsets);
+	symbols[4].address = offsetof(struct dummy_data, post_kernel);
 }
 
 void test_parsing(void)
 {
+	mem = (uint8_t *) &dummy_data;
 	test_init();
 	int ret = RTOS_UpdateThreads();
 	TEST_ASSERT(ret == 0);
@@ -295,8 +329,41 @@ void test_parsing(void)
 	RTOS_Init(&api, 0);
 }
 
+void test_boot(void)
+{
+	mem = (uint8_t *) &boot_dummy_data;
+	test_init();
+
+	// Order of calls matches what is seen from JlinkGDBServer
+	uint32_t n = RTOS_GetNumThreads();
+	TEST_CHECK(n == 1);
+
+	int ret = RTOS_UpdateThreads();
+	TEST_ASSERT(ret == -1);
+
+	TEST_CHECK(RTOS_GetThreadId(0) == GDB_NO_THREAD);
+
+	char display[32];
+	ret = RTOS_GetThreadDisplay(display, GDB_NO_THREAD);
+	TEST_ASSERT(ret > 0);
+
+	n = RTOS_GetNumThreads();
+	TEST_CHECK(n == 1);
+
+	uint32_t id = RTOS_GetCurrentThreadId();
+	TEST_CHECK(id == GDB_NO_THREAD);
+
+	char val[10];
+	ret = RTOS_GetThreadReg(val, RTOS_PLUGIN_CPU_REG_CORTEX_M_PC, id);
+	TEST_CHECK(ret == -1);
+
+	// Force clear
+	RTOS_Init(&api, 0);
+}
+
 TEST_LIST = {
    { "test_init", test_init },
    { "test_parsing", test_parsing},
+   { "test_boot", test_boot},
    { NULL, NULL }     /* zeroed record marking the end of the list */
 };

zephyr_plugin.c

@@ -38,6 +38,11 @@
 #define JLINK_CORE_CORTEX_M7        0x0E0100FF
 #define JLINK_CORE_CORTEX_M_V8MAINL 0x0E0200FF
 
+/**
+ * Magic number used by GDB when no thread is running.
+ */
+#define GDB_NO_THREAD   0xDEAD
+
 /**
  * List of debug information that Zephyr exposes.
  *
@@ -168,7 +173,7 @@ bool threads_updated = false;
 /** Head of thread list */
 struct thread_t *threads_head = NULL;
 /** Currently running thread */
-uint32_t current_base = 0;
+uint32_t current_base = GDB_NO_THREAD;
 /* size_t size */
 uint8_t size_t_size = 0;
 /** Num thread offset */
@@ -238,7 +243,7 @@ static void clear(void)
         p = q;
     }
     threads_head = NULL;
-    current_base = 0;
+    current_base = GDB_NO_THREAD;
 }
 
 struct thread_t *base_to_thread(uint32_t base) {
@@ -291,7 +296,8 @@ static void update_handler_thread(void)
 #endif
         t = new_thread();
         sprintf(t->name, "EXCEPTION/INTERRUPT");
-        current_base = 0;
+        t->base = GDB_NO_THREAD;
+        current_base = GDB_NO_THREAD;
     }
 }
 
@@ -555,7 +561,7 @@ EXPORT uint32_t RTOS_GetThreadId(uint32_t n) {
     if (t)
         return t->base;
     else
-        return 0;
+        return current_base;
 }
 
 EXPORT int RTOS_GetThreadDisplay(char *pDisplay, uint32_t threadid) {
@@ -753,7 +759,7 @@ EXPORT int RTOS_UpdateThreads(void) {
 
 EXPORT uint32_t RTOS_GetNumThreads(void) {
 #if !defined(_NO_DEBUG_LOG) && VERBOSE_LOGGING
-    api->pfLogOutf("%s() --> %d\n", __func__, n_threads());
+    api->pfLogOutf("%s()\n", __func__);
 #endif
     /* RTOS_GetNumThreads can be called before RTOS_UpdateThreads when first
      * attaching a debugger. As RTOS_UpdateThreads populates the thread
@@ -763,9 +769,17 @@ EXPORT uint32_t RTOS_GetNumThreads(void) {
      * immediately.
      */
     if (!threads_updated) {
-        if (RTOS_UpdateThreads() < 0) {
-            return 0;
-        }
+        RTOS_UpdateThreads();
+    }
+    uint32_t threads = n_threads();
+    /* GDB gets confused if there is no thread running. Consider the current
+     * execution context a thread even if the kernel has not started yet.
+     */
+    if( threads == 0 ) {
+        threads = 1;
     }
-    return n_threads();
+#if !defined(_NO_DEBUG_LOG) && VERBOSE_LOGGING
+    api->pfLogOutf("%s() returned %u\n", __func__, threads);
+#endif
+    return threads;
 }