[system/tools]: gdbstub support C3

Closes IDF-1757
Closes IDF-2489

components/esp_gdbstub/riscv/gdbstub_riscv.c

@@ -0,0 +1,60 @@
+// Copyright 2015-2019 Espressif Systems (Shanghai) PTE LTD
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include <string.h>
+#include "esp_gdbstub.h"
+#include "esp_gdbstub_common.h"
+#include "soc/cpu.h"
+#include "sdkconfig.h"
+#include "freertos/FreeRTOS.h"
+#include "freertos/task.h"
+
+static void init_regfile(esp_gdbstub_gdb_regfile_t *dst)
+{
+    memset(dst, 0, sizeof(*dst));
+}
+
+void esp_gdbstub_frame_to_regfile(const esp_gdbstub_frame_t *frame, esp_gdbstub_gdb_regfile_t *dst)
+{
+    init_regfile(dst);
+    dst->pc = frame->mepc;
+
+    // We omit register x0 here since it's the zero register and always hard-wired to 0.
+    // See The RISC-V Instruction Set Manual Volume I: Unprivileged ISA Document Version 20191213 for more details.
+    memcpy(&(dst->x[1]), &frame->ra, sizeof(uint32_t) * 31);
+}
+
+#ifdef CONFIG_ESP_GDBSTUB_SUPPORT_TASKS
+
+/* Represents FreeRTOS TCB structure */
+typedef struct {
+    uint8_t *top_of_stack;
+    /* Other members aren't needed */
+} dummy_tcb_t;
+
+
+void esp_gdbstub_tcb_to_regfile(TaskHandle_t tcb, esp_gdbstub_gdb_regfile_t *dst)
+{
+    const dummy_tcb_t *dummy_tcb = (const dummy_tcb_t *) tcb;
+
+    const RvExcFrame *frame = (RvExcFrame *) dummy_tcb->top_of_stack;
+    esp_gdbstub_frame_to_regfile(frame, dst);
+}
+
+#endif // CONFIG_ESP_GDBSTUB_SUPPORT_TASKS
+
+int esp_gdbstub_get_signal(const esp_gdbstub_frame_t *frame)
+{
+      return 5; // SIGTRAP, see IDF-2490
+}