9 files changed, 750 insertions, 0 deletions

diff --git a/scripts/gdb/linux/.gitignore b/scripts/gdb/linux/.gitignore
new file mode 100644
index 000000000000..52e4e61140d1
--- /dev/null
+++ b/scripts/gdb/linux/.gitignore
@@ -0,0 +1,2 @@
+*.pyc
+*.pyo
diff --git a/scripts/gdb/linux/Makefile b/scripts/gdb/linux/Makefile
new file mode 100644
index 000000000000..6cf1ecf61057
--- /dev/null
+++ b/scripts/gdb/linux/Makefile
@@ -0,0 +1,11 @@
+always := gdb-scripts
+
+SRCTREE := $(shell cd $(srctree) && /bin/pwd)
+
+$(obj)/gdb-scripts:
+ifneq ($(KBUILD_SRC),)
+        $(Q)ln -fsn $(SRCTREE)/$(obj)/*.py $(objtree)/$(obj)
+endif
+        @:
+
+clean-files := *.pyc *.pyo $(if $(KBUILD_SRC),*.py)
diff --git a/scripts/gdb/linux/__init__.py b/scripts/gdb/linux/__init__.py
new file mode 100644
index 000000000000..4680fb176337
--- /dev/null
+++ b/scripts/gdb/linux/__init__.py
@@ -0,0 +1 @@
+# nothing to do for the initialization of this package
diff --git a/scripts/gdb/linux/cpus.py b/scripts/gdb/linux/cpus.py
new file mode 100644
index 000000000000..4297b83fedef
--- /dev/null
+++ b/scripts/gdb/linux/cpus.py
@@ -0,0 +1,135 @@
+#
+# gdb helper commands and functions for Linux kernel debugging
+#
+#  per-cpu tools
+#
+# Copyright (c) Siemens AG, 2011-2013
+#
+# Authors:
+#  Jan Kiszka <jan.kiszka@siemens.com>
+#
+# This work is licensed under the terms of the GNU GPL version 2.
+#
+
+import gdb
+
+from linux import tasks, utils
+
+
+MAX_CPUS = 4096
+
+
+def get_current_cpu():
+    if utils.get_gdbserver_type() == utils.GDBSERVER_QEMU:
+        return gdb.selected_thread().num - 1
+    elif utils.get_gdbserver_type() == utils.GDBSERVER_KGDB:
+        tid = gdb.selected_thread().ptid[2]
+        if tid > (0x100000000 - MAX_CPUS - 2):
+            return 0x100000000 - tid - 2
+        else:
+            return tasks.get_thread_info(tasks.get_task_by_pid(tid))['cpu']
+    else:
+        raise gdb.GdbError("Sorry, obtaining the current CPU is not yet "
+                           "supported with this gdb server.")
+
+
+def per_cpu(var_ptr, cpu):
+    if cpu == -1:
+        cpu = get_current_cpu()
+    if utils.is_target_arch("sparc:v9"):
+        offset = gdb.parse_and_eval(
+            "trap_block[{0}].__per_cpu_base".format(str(cpu)))
+    else:
+        try:
+            offset = gdb.parse_and_eval(
+                "__per_cpu_offset[{0}]".format(str(cpu)))
+        except gdb.error:
+            # !CONFIG_SMP case
+            offset = 0
+    pointer = var_ptr.cast(utils.get_long_type()) + offset
+    return pointer.cast(var_ptr.type).dereference()
+
+
+cpu_mask = {}
+
+
+def cpu_mask_invalidate(event):
+    global cpu_mask
+    cpu_mask = {}
+    gdb.events.stop.disconnect(cpu_mask_invalidate)
+    if hasattr(gdb.events, 'new_objfile'):
+        gdb.events.new_objfile.disconnect(cpu_mask_invalidate)
+
+
+def cpu_list(mask_name):
+    global cpu_mask
+    mask = None
+    if mask_name in cpu_mask:
+        mask = cpu_mask[mask_name]
+    if mask is None:
+        mask = gdb.parse_and_eval(mask_name + ".bits")
+        if hasattr(gdb, 'events'):
+            cpu_mask[mask_name] = mask
+            gdb.events.stop.connect(cpu_mask_invalidate)
+            if hasattr(gdb.events, 'new_objfile'):
+                gdb.events.new_objfile.connect(cpu_mask_invalidate)
+    bits_per_entry = mask[0].type.sizeof * 8
+    num_entries = mask.type.sizeof * 8 / bits_per_entry
+    entry = -1
+    bits = 0
+
+    while True:
+        while bits == 0:
+            entry += 1
+            if entry == num_entries:
+                return
+            bits = mask[entry]
+            if bits != 0:
+                bit = 0
+                break
+
+        while bits & 1 == 0:
+            bits >>= 1
+            bit += 1
+
+        cpu = entry * bits_per_entry + bit
+
+        bits >>= 1
+        bit += 1
+
+        yield cpu
+
+
+class PerCpu(gdb.Function):
+    """Return per-cpu variable.
+
+$lx_per_cpu("VAR"[, CPU]): Return the per-cpu variable called VAR for the
+given CPU number. If CPU is omitted, the CPU of the current context is used.
+Note that VAR has to be quoted as string."""
+
+    def __init__(self):
+        super(PerCpu, self).__init__("lx_per_cpu")
+
+    def invoke(self, var_name, cpu=-1):
+        var_ptr = gdb.parse_and_eval("&" + var_name.string())
+        return per_cpu(var_ptr, cpu)
+
+
+PerCpu()
+
+
+class LxCurrentFunc(gdb.Function):
+    """Return current task.
+
+$lx_current([CPU]): Return the per-cpu task variable for the given CPU
+number. If CPU is omitted, the CPU of the current context is used."""
+
+    def __init__(self):
+        super(LxCurrentFunc, self).__init__("lx_current")
+
+    def invoke(self, cpu=-1):
+        var_ptr = gdb.parse_and_eval("&current_task")
+        return per_cpu(var_ptr, cpu).dereference()
+
+
+LxCurrentFunc()
diff --git a/scripts/gdb/linux/dmesg.py b/scripts/gdb/linux/dmesg.py
new file mode 100644
index 000000000000..3c947f0c5dad
--- /dev/null
+++ b/scripts/gdb/linux/dmesg.py
@@ -0,0 +1,65 @@
+#
+# gdb helper commands and functions for Linux kernel debugging
+#
+#  kernel log buffer dump
+#
+# Copyright (c) Siemens AG, 2011, 2012
+#
+# Authors:
+#  Jan Kiszka <jan.kiszka@siemens.com>
+#
+# This work is licensed under the terms of the GNU GPL version 2.
+#
+
+import gdb
+import string
+
+from linux import utils
+
+
+class LxDmesg(gdb.Command):
+    """Print Linux kernel log buffer."""
+
+    def __init__(self):
+        super(LxDmesg, self).__init__("lx-dmesg", gdb.COMMAND_DATA)
+
+    def invoke(self, arg, from_tty):
+        log_buf_addr = int(str(gdb.parse_and_eval("log_buf")).split()[0], 16)
+        log_first_idx = int(gdb.parse_and_eval("log_first_idx"))
+        log_next_idx = int(gdb.parse_and_eval("log_next_idx"))
+        log_buf_len = int(gdb.parse_and_eval("log_buf_len"))
+
+        inf = gdb.inferiors()[0]
+        start = log_buf_addr + log_first_idx
+        if log_first_idx < log_next_idx:
+            log_buf_2nd_half = -1
+            length = log_next_idx - log_first_idx
+            log_buf = inf.read_memory(start, length)
+        else:
+            log_buf_2nd_half = log_buf_len - log_first_idx
+            log_buf = inf.read_memory(start, log_buf_2nd_half) + \
+                inf.read_memory(log_buf_addr, log_next_idx)
+
+        pos = 0
+        while pos < log_buf.__len__():
+            length = utils.read_u16(log_buf[pos + 8:pos + 10])
+            if length == 0:
+                if log_buf_2nd_half == -1:
+                    gdb.write("Corrupted log buffer!\n")
+                    break
+                pos = log_buf_2nd_half
+                continue
+
+            text_len = utils.read_u16(log_buf[pos + 10:pos + 12])
+            text = log_buf[pos + 16:pos + 16 + text_len]
+            time_stamp = utils.read_u64(log_buf[pos:pos + 8])
+
+            for line in memoryview(text).tobytes().splitlines():
+                gdb.write("[{time:12.6f}] {line}\n".format(
+                    time=time_stamp / 1000000000.0,
+                    line=line))
+
+            pos += length
+
+
+LxDmesg()
diff --git a/scripts/gdb/linux/modules.py b/scripts/gdb/linux/modules.py
new file mode 100644
index 000000000000..a1504c4f1900
--- /dev/null
+++ b/scripts/gdb/linux/modules.py
@@ -0,0 +1,103 @@
+#
+# gdb helper commands and functions for Linux kernel debugging
+#
+#  module tools
+#
+# Copyright (c) Siemens AG, 2013
+#
+# Authors:
+#  Jan Kiszka <jan.kiszka@siemens.com>
+#
+# This work is licensed under the terms of the GNU GPL version 2.
+#
+
+import gdb
+
+from linux import cpus, utils
+
+
+module_type = utils.CachedType("struct module")
+
+
+def module_list():
+    global module_type
+    module_ptr_type = module_type.get_type().pointer()
+    modules = gdb.parse_and_eval("modules")
+    entry = modules['next']
+    end_of_list = modules.address
+
+    while entry != end_of_list:
+        yield utils.container_of(entry, module_ptr_type, "list")
+        entry = entry['next']
+
+
+def find_module_by_name(name):
+    for module in module_list():
+        if module['name'].string() == name:
+            return module
+    return None
+
+
+class LxModule(gdb.Function):
+    """Find module by name and return the module variable.
+
+$lx_module("MODULE"): Given the name MODULE, iterate over all loaded modules
+of the target and return that module variable which MODULE matches."""
+
+    def __init__(self):
+        super(LxModule, self).__init__("lx_module")
+
+    def invoke(self, mod_name):
+        mod_name = mod_name.string()
+        module = find_module_by_name(mod_name)
+        if module:
+            return module.dereference()
+        else:
+            raise gdb.GdbError("Unable to find MODULE " + mod_name)
+
+
+LxModule()
+
+
+class LxLsmod(gdb.Command):
+    """List currently loaded modules."""
+
+    _module_use_type = utils.CachedType("struct module_use")
+
+    def __init__(self):
+        super(LxLsmod, self).__init__("lx-lsmod", gdb.COMMAND_DATA)
+
+    def invoke(self, arg, from_tty):
+        gdb.write(
+            "Address{0}    Module                  Size  Used by\n".format(
+                "        " if utils.get_long_type().sizeof == 8 else ""))
+
+        for module in module_list():
+            ref = 0
+            module_refptr = module['refptr']
+            for cpu in cpus.cpu_list("cpu_possible_mask"):
+                refptr = cpus.per_cpu(module_refptr, cpu)
+                ref += refptr['incs']
+                ref -= refptr['decs']
+
+            gdb.write("{address} {name:<19} {size:>8}  {ref}".format(
+                address=str(module['module_core']).split()[0],
+                name=module['name'].string(),
+                size=str(module['core_size']),
+                ref=str(ref)))
+
+            source_list = module['source_list']
+            t = self._module_use_type.get_type().pointer()
+            entry = source_list['next']
+            first = True
+            while entry != source_list.address:
+                use = utils.container_of(entry, t, "source_list")
+                gdb.write("{separator}{name}".format(
+                    separator=" " if first else ",",
+                    name=use['source']['name'].string()))
+                first = False
+                entry = entry['next']
+            gdb.write("\n")
+
+
+LxLsmod()
diff --git a/scripts/gdb/linux/symbols.py b/scripts/gdb/linux/symbols.py
new file mode 100644
index 000000000000..cd5bea965d4e
--- /dev/null
+++ b/scripts/gdb/linux/symbols.py
@@ -0,0 +1,177 @@
+#
+# gdb helper commands and functions for Linux kernel debugging
+#
+#  load kernel and module symbols
+#
+# Copyright (c) Siemens AG, 2011-2013
+#
+# Authors:
+#  Jan Kiszka <jan.kiszka@siemens.com>
+#
+# This work is licensed under the terms of the GNU GPL version 2.
+#
+
+import gdb
+import os
+import re
+import string
+
+from linux import modules, utils
+
+
+if hasattr(gdb, 'Breakpoint'):
+    class LoadModuleBreakpoint(gdb.Breakpoint):
+        def __init__(self, spec, gdb_command):
+            super(LoadModuleBreakpoint, self).__init__(spec, internal=True)
+            self.silent = True
+            self.gdb_command = gdb_command
+
+        def stop(self):
+            module = gdb.parse_and_eval("mod")
+            module_name = module['name'].string()
+            cmd = self.gdb_command
+
+            # enforce update if object file is not found
+            cmd.module_files_updated = False
+
+            # Disable pagination while reporting symbol (re-)loading.
+            # The console input is blocked in this context so that we would
+            # get stuck waiting for the user to acknowledge paged output.
+            show_pagination = gdb.execute("show pagination", to_string=True)
+            pagination = show_pagination.endswith("on.\n")
+            gdb.execute("set pagination off")
+
+            if module_name in cmd.loaded_modules:
+                gdb.write("refreshing all symbols to reload module "
+                          "'{0}'\n".format(module_name))
+                cmd.load_all_symbols()
+            else:
+                cmd.load_module_symbols(module)
+
+            # restore pagination state
+            gdb.execute("set pagination %s" % ("on" if pagination else "off"))
+
+            return False
+
+
+class LxSymbols(gdb.Command):
+    """(Re-)load symbols of Linux kernel and currently loaded modules.
+
+The kernel (vmlinux) is taken from the current working directly. Modules (.ko)
+are scanned recursively, starting in the same directory. Optionally, the module
+search path can be extended by a space separated list of paths passed to the
+lx-symbols command."""
+
+    module_paths = []
+    module_files = []
+    module_files_updated = False
+    loaded_modules = []
+    breakpoint = None
+
+    def __init__(self):
+        super(LxSymbols, self).__init__("lx-symbols", gdb.COMMAND_FILES,
+                                        gdb.COMPLETE_FILENAME)
+
+    def _update_module_files(self):
+        self.module_files = []
+        for path in self.module_paths:
+            gdb.write("scanning for modules in {0}\n".format(path))
+            for root, dirs, files in os.walk(path):
+                for name in files:
+                    if name.endswith(".ko"):
+                        self.module_files.append(root + "/" + name)
+        self.module_files_updated = True
+
+    def _get_module_file(self, module_name):
+        module_pattern = ".*/{0}\.ko$".format(
+            module_name.replace("_", r"[_\-]"))
+        for name in self.module_files:
+            if re.match(module_pattern, name) and os.path.exists(name):
+                return name
+        return None
+
+    def _section_arguments(self, module):
+        try:
+            sect_attrs = module['sect_attrs'].dereference()
+        except gdb.error:
+            return ""
+        attrs = sect_attrs['attrs']
+        section_name_to_address = {
+            attrs[n]['name'].string() : attrs[n]['address']
+            for n in range(int(sect_attrs['nsections']))}
+        args = []
+        for section_name in [".data", ".data..read_mostly", ".rodata", ".bss"]:
+            address = section_name_to_address.get(section_name)
+            if address:
+                args.append(" -s {name} {addr}".format(
+                    name=section_name, addr=str(address)))
+        return "".join(args)
+
+    def load_module_symbols(self, module):
+        module_name = module['name'].string()
+        module_addr = str(module['module_core']).split()[0]
+
+        module_file = self._get_module_file(module_name)
+        if not module_file and not self.module_files_updated:
+            self._update_module_files()
+            module_file = self._get_module_file(module_name)
+
+        if module_file:
+            gdb.write("loading @{addr}: {filename}\n".format(
+                addr=module_addr, filename=module_file))
+            cmdline = "add-symbol-file {filename} {addr}{sections}".format(
+                filename=module_file,
+                addr=module_addr,
+                sections=self._section_arguments(module))
+            gdb.execute(cmdline, to_string=True)
+            if not module_name in self.loaded_modules:
+                self.loaded_modules.append(module_name)
+        else:
+            gdb.write("no module object found for '{0}'\n".format(module_name))
+
+    def load_all_symbols(self):
+        gdb.write("loading vmlinux\n")
+
+        # Dropping symbols will disable all breakpoints. So save their states
+        # and restore them afterward.
+        saved_states = []
+        if hasattr(gdb, 'breakpoints') and not gdb.breakpoints() is None:
+            for bp in gdb.breakpoints():
+                saved_states.append({'breakpoint': bp, 'enabled': bp.enabled})
+
+        # drop all current symbols and reload vmlinux
+        gdb.execute("symbol-file", to_string=True)
+        gdb.execute("symbol-file vmlinux")
+
+        self.loaded_modules = []
+        module_list = modules.module_list()
+        if not module_list:
+            gdb.write("no modules found\n")
+        else:
+            [self.load_module_symbols(module) for module in module_list]
+
+        for saved_state in saved_states:
+            saved_state['breakpoint'].enabled = saved_state['enabled']
+
+    def invoke(self, arg, from_tty):
+        self.module_paths = arg.split()
+        self.module_paths.append(os.getcwd())
+
+        # enforce update
+        self.module_files = []
+        self.module_files_updated = False
+
+        self.load_all_symbols()
+
+        if hasattr(gdb, 'Breakpoint'):
+            if not self.breakpoint is None:
+                self.breakpoint.delete()
+                self.breakpoint = None
+            self.breakpoint = LoadModuleBreakpoint(
+                "kernel/module.c:do_init_module", self)
+        else:
+            gdb.write("Note: symbol update on module loading not supported "
+                      "with this gdb version\n")
+
+
+LxSymbols()
diff --git a/scripts/gdb/linux/tasks.py b/scripts/gdb/linux/tasks.py
new file mode 100644
index 000000000000..e2037d9bb7eb
--- /dev/null
+++ b/scripts/gdb/linux/tasks.py
@@ -0,0 +1,100 @@
+#
+# gdb helper commands and functions for Linux kernel debugging
+#
+#  task & thread tools
+#
+# Copyright (c) Siemens AG, 2011-2013
+#
+# Authors:
+#  Jan Kiszka <jan.kiszka@siemens.com>
+#
+# This work is licensed under the terms of the GNU GPL version 2.
+#
+
+import gdb
+
+from linux import utils
+
+
+task_type = utils.CachedType("struct task_struct")
+
+def task_lists():
+    global task_type
+    task_ptr_type = task_type.get_type().pointer()
+    init_task = gdb.parse_and_eval("init_task").address
+    t = g = init_task
+
+    while True:
+        while True:
+            yield t
+
+            t = utils.container_of(t['thread_group']['next'],
+                                   task_ptr_type, "thread_group")
+            if t == g:
+                break
+
+        t = g = utils.container_of(g['tasks']['next'],
+                                   task_ptr_type, "tasks")
+        if t == init_task:
+            return
+
+def get_task_by_pid(pid):
+    for task in task_lists():
+        if int(task['pid']) == pid:
+            return task
+    return None
+
+
+class LxTaskByPidFunc(gdb.Function):
+    """Find Linux task by PID and return the task_struct variable.
+
+$lx_task_by_pid(PID): Given PID, iterate over all tasks of the target and
+return that task_struct variable which PID matches."""
+
+    def __init__(self):
+        super(LxTaskByPidFunc, self).__init__("lx_task_by_pid")
+
+    def invoke(self, pid):
+        task = get_task_by_pid(pid)
+        if task:
+            return task.dereference()
+        else:
+            raise gdb.GdbError("No task of PID " + str(pid))
+
+
+LxTaskByPidFunc()
+
+
+thread_info_type = utils.CachedType("struct thread_info")
+
+ia64_task_size = None
+
+
+def get_thread_info(task):
+    global thread_info_type
+    thread_info_ptr_type = thread_info_type.get_type().pointer()
+    if utils.is_target_arch("ia64"):
+        global ia64_task_size
+        if ia64_task_size is None:
+            ia64_task_size = gdb.parse_and_eval("sizeof(struct task_struct)")
+        thread_info_addr = task.address + ia64_task_size
+        thread_info = thread_info_addr.cast(thread_info_ptr_type)
+    else:
+        thread_info = task['stack'].cast(thread_info_ptr_type)
+    return thread_info.dereference()
+
+
+class LxThreadInfoFunc (gdb.Function):
+    """Calculate Linux thread_info from task variable.
+
+$lx_thread_info(TASK): Given TASK, return the corresponding thread_info
+variable."""
+
+    def __init__(self):
+        super(LxThreadInfoFunc, self).__init__("lx_thread_info")
+
+    def invoke(self, task):
+        return get_thread_info(task)
+
+
+LxThreadInfoFunc()
diff --git a/scripts/gdb/linux/utils.py b/scripts/gdb/linux/utils.py
new file mode 100644
index 000000000000..128c306db3ee
--- /dev/null
+++ b/scripts/gdb/linux/utils.py
@@ -0,0 +1,156 @@
+#
+# gdb helper commands and functions for Linux kernel debugging
+#
+#  common utilities
+#
+# Copyright (c) Siemens AG, 2011-2013
+#
+# Authors:
+#  Jan Kiszka <jan.kiszka@siemens.com>
+#
+# This work is licensed under the terms of the GNU GPL version 2.
+#
+
+import gdb
+
+
+class CachedType:
+    def __init__(self, name):
+        self._type = None
+        self._name = name
+
+    def _new_objfile_handler(self, event):
+        self._type = None
+        gdb.events.new_objfile.disconnect(self._new_objfile_handler)
+
+    def get_type(self):
+        if self._type is None:
+            self._type = gdb.lookup_type(self._name)
+            if self._type is None:
+                raise gdb.GdbError(
+                    "cannot resolve type '{0}'".format(self._name))
+            if hasattr(gdb, 'events') and hasattr(gdb.events, 'new_objfile'):
+                gdb.events.new_objfile.connect(self._new_objfile_handler)
+        return self._type
+
+
+long_type = CachedType("long")
+
+
+def get_long_type():
+    global long_type
+    return long_type.get_type()
+
+
+def offset_of(typeobj, field):
+    element = gdb.Value(0).cast(typeobj)
+    return int(str(element[field].address).split()[0], 16)
+
+
+def container_of(ptr, typeobj, member):
+    return (ptr.cast(get_long_type()) -
+            offset_of(typeobj, member)).cast(typeobj)
+
+
+class ContainerOf(gdb.Function):
+    """Return pointer to containing data structure.
+
+$container_of(PTR, "TYPE", "ELEMENT"): Given PTR, return a pointer to the
+data structure of the type TYPE in which PTR is the address of ELEMENT.
+Note that TYPE and ELEMENT have to be quoted as strings."""
+
+    def __init__(self):
+        super(ContainerOf, self).__init__("container_of")
+
+    def invoke(self, ptr, typename, elementname):
+        return container_of(ptr, gdb.lookup_type(typename.string()).pointer(),
+                            elementname.string())
+
+ContainerOf()
+
+
+BIG_ENDIAN = 0
+LITTLE_ENDIAN = 1
+target_endianness = None
+
+
+def get_target_endianness():
+    global target_endianness
+    if target_endianness is None:
+        endian = gdb.execute("show endian", to_string=True)
+        if "little endian" in endian:
+            target_endianness = LITTLE_ENDIAN
+        elif "big endian" in endian:
+            target_endianness = BIG_ENDIAN
+        else:
+            raise gdb.GdgError("unknown endianness '{0}'".format(str(endian)))
+    return target_endianness
+
+
+def read_u16(buffer):
+    if get_target_endianness() == LITTLE_ENDIAN:
+        return ord(buffer[0]) + (ord(buffer[1]) << 8)
+    else:
+        return ord(buffer[1]) + (ord(buffer[0]) << 8)
+
+
+def read_u32(buffer):
+    if get_target_endianness() == LITTLE_ENDIAN:
+        return read_u16(buffer[0:2]) + (read_u16(buffer[2:4]) << 16)
+    else:
+        return read_u16(buffer[2:4]) + (read_u16(buffer[0:2]) << 16)
+
+
+def read_u64(buffer):
+    if get_target_endianness() == LITTLE_ENDIAN:
+        return read_u32(buffer[0:4]) + (read_u32(buffer[4:8]) << 32)
+    else:
+        return read_u32(buffer[4:8]) + (read_u32(buffer[0:4]) << 32)
+
+
+target_arch = None
+
+
+def is_target_arch(arch):
+    if hasattr(gdb.Frame, 'architecture'):
+        return arch in gdb.newest_frame().architecture().name()
+    else:
+        global target_arch
+        if target_arch is None:
+            target_arch = gdb.execute("show architecture", to_string=True)
+        return arch in target_arch
+
+
+GDBSERVER_QEMU = 0
+GDBSERVER_KGDB = 1
+gdbserver_type = None
+
+
+def get_gdbserver_type():
+    def exit_handler(event):
+        global gdbserver_type
+        gdbserver_type = None
+        gdb.events.exited.disconnect(exit_handler)
+
+    def probe_qemu():
+        try:
+            return gdb.execute("monitor info version", to_string=True) != ""
+        except:
+            return False
+
+    def probe_kgdb():
+        try:
+            thread_info = gdb.execute("info thread 2", to_string=True)
+            return "shadowCPU0" in thread_info
+        except:
+            return False
+
+    global gdbserver_type
+    if gdbserver_type is None:
+        if probe_qemu():
+            gdbserver_type = GDBSERVER_QEMU
+        elif probe_kgdb():
+            gdbserver_type = GDBSERVER_KGDB
+        if not gdbserver_type is None and hasattr(gdb, 'events'):
+            gdb.events.exited.connect(exit_handler)
+    return gdbserver_type