scripts: coredump: coredump_gdbserver in pipeline

Add support to coredump_gdbserver.py for running in a pipeline,
communicating through stdin/stdout instead of a socket.

This allows starting it from inside gdb, with:

    target remote | coredump_gdbserver.py --pipe <elf_file>  <log_file>

Signed-off-by: Kevin ORourke <kevin.orourke@ferroamp.se>

doc/services/debugging/coredump.rst

@@ -55,7 +55,8 @@ This usually involves the following steps:
 
 3. Start the custom GDB server using the script
    :zephyr_file:`scripts/coredump/coredump_gdbserver.py` with the core dump
-   binary log file, and the Zephyr ELF file as parameters.
+   binary log file, and the Zephyr ELF file as parameters. The GDB server
+   can also be started from within GDB, see below.
 
 4. Start the debugger corresponding to the target architecture.
 
@@ -220,6 +221,25 @@ in :file:`coredump.log`:
       #2  0x00100492 in func_1 (addr=0x0) at zephyr/rtos/zephyr/samples/hello_world/src/main.c:28
       #3  0x001004c8 in main () at zephyr/rtos/zephyr/samples/hello_world/src/main.c:42
 
+Starting the GDB server from within GDB
+---------------------------------------
+
+You can use ``target remote |`` to start the custom GDB server from inside
+GDB, instead of in a separate shell.
+
+1. Start GDB:
+
+   .. code-block:: console
+
+      <path to SDK>/x86_64-zephyr-elf/bin/x86_64-zephyr-elf-gdb build/zephyr/zephyr.elf
+
+2. Inside GDB, start the GDB server using the ``--pipe`` option:
+
+   .. code-block:: console
+
+      (gdb) target remote | ./scripts/coredump/coredump_gdbserver.py --pipe build/zephyr/zephyr.elf coredump.bin
+
+
 File Format
 ***********
 

scripts/coredump/coredump_gdbserver.py

@@ -21,6 +21,23 @@ LOGGING_FORMAT = "[%(levelname)s][%(name)s] %(message)s"
 GDBSERVER_HOST = ""
 
 
+class FakeSocket:
+    def __init__(self) -> None:
+        self.in_stream = sys.stdin.buffer
+        self.out_stream = sys.stdout.buffer
+
+    def recv(self, bufsize):
+        return self.in_stream.read(bufsize)
+
+    def send(self, data):
+        n = self.out_stream.write(data)
+        self.out_stream.flush()
+        return n
+
+    def close(self):
+        pass
+
+
 def parse_args():
     parser = argparse.ArgumentParser(allow_abbrev=False)
 
@@ -30,6 +47,8 @@ def parse_args():
                         help="Print extra debugging information")
     parser.add_argument("--port", type=int, default=1234,
                         help="GDB server port")
+    parser.add_argument("--pipe", action="store_true",
+                        help="Use stdio to communicate with gdb")
     parser.add_argument("-v", "--verbose", action="store_true",
                         help="Print more information")
 
@@ -99,19 +118,23 @@ def main():
 
     gdbstub = gdbstubs.get_gdbstub(logf, elff)
 
-    # Start a GDB server
-    gdbserver = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
+    if not args.pipe:
+        # Start a GDB server
+        gdbserver = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
 
-    # Reuse address so we don't have to wait for socket to be
-    # close before we can bind to the port again
-    gdbserver.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
+        # Reuse address so we don't have to wait for socket to be
+        # close before we can bind to the port again
+        gdbserver.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
 
-    gdbserver.bind((GDBSERVER_HOST, args.port))
-    gdbserver.listen(1)
+        gdbserver.bind((GDBSERVER_HOST, args.port))
+        gdbserver.listen(1)
 
-    logger.info(f"Waiting GDB connection on port {args.port}...")
+        logger.info(f"Waiting GDB connection on port {args.port}...")
 
-    conn, remote = gdbserver.accept()
+        conn, remote = gdbserver.accept()
+    else:
+        conn = FakeSocket()
+        remote = "pipe"
 
     if conn:
         logger.info(f"Accepted GDB connection from {remote}")