* [PATCH 1/2] scripts/gdb/radix-tree: add lx-radix-tree-command
2025-07-10 11:53 [PATCH 0/2] scripts/gdb/symbols: make BPF debug info available to GDB Ilya Leoshkevich
@ 2025-07-10 11:53 ` Ilya Leoshkevich
2025-07-10 11:53 ` [PATCH 2/2] scripts/gdb/symbols: make BPF debug info available to GDB Ilya Leoshkevich
2025-08-05 13:22 ` [PATCH 0/2] " Ilya Leoshkevich
2 siblings, 0 replies; 6+ messages in thread
From: Ilya Leoshkevich @ 2025-07-10 11:53 UTC (permalink / raw)
To: Alexei Starovoitov, Daniel Borkmann, Andrii Nakryiko, Jan Kiszka,
Kieran Bingham
Cc: linux-kernel, bpf, Heiko Carstens, Vasily Gorbik,
Alexander Gordeev, Ilya Leoshkevich
Add a function and a command to iterate over radix tree contents.
Duplicate the C implementation in Python, but drop support for tagging.
Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
---
scripts/gdb/linux/radixtree.py | 139 +++++++++++++++++++++++++++++++--
1 file changed, 132 insertions(+), 7 deletions(-)
diff --git a/scripts/gdb/linux/radixtree.py b/scripts/gdb/linux/radixtree.py
index 074543ac763d..bc2954e45c32 100644
--- a/scripts/gdb/linux/radixtree.py
+++ b/scripts/gdb/linux/radixtree.py
@@ -30,13 +30,16 @@ def entry_to_node(node):
def node_maxindex(node):
return (constants.LX_RADIX_TREE_MAP_SIZE << node['shift']) - 1
-def lookup(root, index):
+def resolve_root(root):
+ if root.type == radix_tree_root_type.get_type():
+ return root
if root.type == radix_tree_root_type.get_type().pointer():
- node = root.dereference()
- elif root.type != radix_tree_root_type.get_type():
- raise gdb.GdbError("must be {} not {}"
- .format(radix_tree_root_type.get_type(), root.type))
+ return root.dereference()
+ raise gdb.GdbError("must be {} not {}"
+ .format(radix_tree_root_type.get_type(), root.type))
+def lookup(root, index):
+ root = resolve_root(root)
node = root['xa_head']
if node == 0:
return None
@@ -71,14 +74,120 @@ def lookup(root, index):
return node
-class LxRadixTree(gdb.Function):
+def descend(parent, index):
+ offset = (index >> int(parent["shift"])) & constants.LX_RADIX_TREE_MAP_MASK
+ return offset, parent["slots"][offset]
+
+def load_root(root):
+ node = root["xa_head"]
+ nodep = node
+
+ if is_internal_node(node):
+ node = entry_to_node(node)
+ maxindex = node_maxindex(node)
+ return int(node["shift"]) + constants.LX_RADIX_TREE_MAP_SHIFT, \
+ nodep, maxindex
+
+ return 0, nodep, 0
+
+class RadixTreeIter:
+ def __init__(self, start):
+ self.index = 0
+ self.next_index = start
+ self.node = None
+
+def xa_mk_internal(v):
+ return (v << 2) | 2
+
+LX_XA_RETRY_ENTRY = xa_mk_internal(256)
+LX_RADIX_TREE_RETRY = LX_XA_RETRY_ENTRY
+
+def next_chunk(root, iter):
+ mask = (1 << (utils.get_ulong_type().sizeof * 8)) - 1
+
+ index = iter.next_index
+ if index == 0 and iter.index != 0:
+ return None
+
+ restart = True
+ while restart:
+ restart = False
+
+ _, child, maxindex = load_root(root)
+ if index > maxindex:
+ return None
+ if not child:
+ return None
+
+ if not is_internal_node(child):
+ iter.index = index
+ iter.next_index = (maxindex + 1) & mask
+ iter.node = None
+ return root["xa_head"].address
+
+ while True:
+ node = entry_to_node(child)
+ offset, child = descend(node, index)
+
+ if not child:
+ while True:
+ offset += 1
+ if offset >= constants.LX_RADIX_TREE_MAP_SIZE:
+ break
+ slot = node["slots"][offset]
+ if slot:
+ break
+ index &= ~node_maxindex(node)
+ index = (index + (offset << int(node["shift"]))) & mask
+ if index == 0:
+ return None
+ if offset == constants.LX_RADIX_TREE_MAP_SIZE:
+ restart = True
+ break
+ child = node["slots"][offset]
+
+ if not child:
+ restart = True
+ break
+ if child == LX_XA_RETRY_ENTRY:
+ break
+ if not node["shift"] or not is_internal_node(child):
+ break
+
+ iter.index = (index & ~node_maxindex(node)) | offset
+ iter.next_index = ((index | node_maxindex(node)) + 1) & mask
+ iter.node = node
+
+ return node["slots"][offset].address
+
+def next_slot(slot, iter):
+ mask = (1 << (utils.get_ulong_type().sizeof * 8)) - 1
+ for _ in range(iter.next_index - iter.index - 1):
+ slot += 1
+ iter.index = (iter.index + 1) & mask
+ if slot.dereference():
+ return slot
+ return None
+
+def for_each_slot(root, start=0):
+ iter = RadixTreeIter(start)
+ slot = None
+ while True:
+ if not slot:
+ slot = next_chunk(root, iter)
+ if not slot:
+ break
+ yield iter.index, slot
+ slot = next_slot(slot, iter)
+
+class LxRadixTreeLookup(gdb.Function):
""" Lookup and return a node from a RadixTree.
$lx_radix_tree_lookup(root_node [, index]): Return the node at the given index.
If index is omitted, the root node is dereference and returned."""
def __init__(self):
- super(LxRadixTree, self).__init__("lx_radix_tree_lookup")
+ super(LxRadixTreeLookup, self).__init__("lx_radix_tree_lookup")
def invoke(self, root, index=0):
result = lookup(root, index)
@@ -87,4 +196,20 @@ If index is omitted, the root node is dereference and returned."""
return result
+class LxRadixTree(gdb.Command):
+ """Show all values stored in a RadixTree."""
+
+ def __init__(self):
+ super(LxRadixTree, self).__init__("lx-radix-tree", gdb.COMMAND_DATA,
+ gdb.COMPLETE_NONE)
+
+ def invoke(self, argument, from_tty):
+ args = gdb.string_to_argv(argument)
+ if len(args) != 1:
+ raise gdb.GdbError("Usage: lx-radix-tree ROOT")
+ root = gdb.parse_and_eval(args[0])
+ for index, slot in for_each_slot(root):
+ gdb.write("[{}] = {}\n".format(index, slot.dereference()))
+
LxRadixTree()
+LxRadixTreeLookup()
--
2.50.0
^ permalink raw reply related [flat|nested] 6+ messages in thread* [PATCH 2/2] scripts/gdb/symbols: make BPF debug info available to GDB
2025-07-10 11:53 [PATCH 0/2] scripts/gdb/symbols: make BPF debug info available to GDB Ilya Leoshkevich
2025-07-10 11:53 ` [PATCH 1/2] scripts/gdb/radix-tree: add lx-radix-tree-command Ilya Leoshkevich
@ 2025-07-10 11:53 ` Ilya Leoshkevich
2025-08-05 13:22 ` [PATCH 0/2] " Ilya Leoshkevich
2 siblings, 0 replies; 6+ messages in thread
From: Ilya Leoshkevich @ 2025-07-10 11:53 UTC (permalink / raw)
To: Alexei Starovoitov, Daniel Borkmann, Andrii Nakryiko, Jan Kiszka,
Kieran Bingham
Cc: linux-kernel, bpf, Heiko Carstens, Vasily Gorbik,
Alexander Gordeev, Ilya Leoshkevich
One can debug BPF programs with QEMU gdbstub by setting a breakpoint
on bpf_prog_kallsyms_add(), waiting for a hit with a matching
aux.name, and then setting a breakpoint on bpf_func. This is tedious,
error-prone, and also lacks line numbers.
Automate this in a way similar to the existing support for modules in
lx-symbols.
Enumerate and monitor changes to both BPF kallsyms and JITed progs. For
each ksym, generate and compile a synthetic .s file containing the
name, code, and size. In addition, if this ksym is also a prog, and not
a trampoline, add line number information.
Ensure that this is a no-op if the kernel is built without BPF support
or if "as" is missing. In theory the "as" dependency may be dropped by
generating the synthetic .o file manually, but this is too much
complexity for too little benefit.
Now one can debug BPF progs out of the box like this:
(gdb) lx-symbols
(gdb) b bpf_prog_4e612a6a881a086b_arena_list_add
Breakpoint 2 (bpf_prog_4e612a6a881a086b_arena_list_add) pending.
# ./test_progs -t arena_list
Thread 4 hit Breakpoint 2, bpf_prog_4e612a6a881a086b_arena_list_add ()
at linux/tools/testing/selftests/bpf/progs/arena_list.c:51
51 list_head = &global_head;
(gdb) n
bpf_prog_4e612a6a881a086b_arena_list_add () at linux/tools/testing/selftests/bpf/progs/arena_list.c:53
53 for (i = zero; i < cnt && can_loop; i++) {
This also works for subprogs.
Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
---
scripts/gdb/linux/bpf.py | 253 ++++++++++++++++++++++++++++++
scripts/gdb/linux/constants.py.in | 3 +
scripts/gdb/linux/symbols.py | 77 ++++++++-
3 files changed, 330 insertions(+), 3 deletions(-)
create mode 100644 scripts/gdb/linux/bpf.py
diff --git a/scripts/gdb/linux/bpf.py b/scripts/gdb/linux/bpf.py
new file mode 100644
index 000000000000..c2ec244cc94b
--- /dev/null
+++ b/scripts/gdb/linux/bpf.py
@@ -0,0 +1,253 @@
+# SPDX-License-Identifier: GPL-2.0
+
+import json
+import subprocess
+import tempfile
+
+import gdb
+
+from linux import constants, lists, radixtree, utils
+
+
+if constants.LX_CONFIG_BPF and constants.LX_CONFIG_BPF_JIT:
+ bpf_ksym_type = utils.CachedType("struct bpf_ksym")
+if constants.LX_CONFIG_BPF_SYSCALL:
+ bpf_prog_type = utils.CachedType("struct bpf_prog")
+
+
+def get_ksym_name(ksym):
+ name = ksym["name"].bytes
+ end = name.find(b"\x00")
+ if end != -1:
+ name = name[:end]
+ return name.decode()
+
+
+def list_ksyms():
+ if not (constants.LX_CONFIG_BPF and constants.LX_CONFIG_BPF_JIT):
+ return []
+ bpf_kallsyms = gdb.parse_and_eval("&bpf_kallsyms")
+ bpf_ksym_ptr_type = bpf_ksym_type.get_type().pointer()
+ return list(lists.list_for_each_entry(bpf_kallsyms,
+ bpf_ksym_ptr_type,
+ "lnode"))
+
+
+class KsymAddBreakpoint(gdb.Breakpoint):
+ def __init__(self, monitor):
+ super(KsymAddBreakpoint, self).__init__("bpf_ksym_add", internal=True)
+ self.silent = True
+ self.monitor = monitor
+
+ def stop(self):
+ self.monitor.add(gdb.parse_and_eval("ksym"))
+ return False
+
+
+class KsymRemoveBreakpoint(gdb.Breakpoint):
+ def __init__(self, monitor):
+ super(KsymRemoveBreakpoint, self).__init__("bpf_ksym_del",
+ internal=True)
+ self.silent = True
+ self.monitor = monitor
+
+ def stop(self):
+ self.monitor.remove(gdb.parse_and_eval("ksym"))
+ return False
+
+
+class KsymMonitor:
+ def __init__(self, add, remove):
+ self.add = add
+ self.remove = remove
+
+ self.add_bp = KsymAddBreakpoint(self)
+ self.remove_bp = KsymRemoveBreakpoint(self)
+
+ self.notify_initial()
+
+ def notify_initial(self):
+ for ksym in list_ksyms():
+ self.add(ksym)
+
+ def close(self):
+ self.add_bp.delete()
+ self.remove_bp.delete()
+
+
+def list_progs():
+ if not constants.LX_CONFIG_BPF_SYSCALL:
+ return []
+ idr_rt = gdb.parse_and_eval("&prog_idr.idr_rt")
+ bpf_prog_ptr_type = bpf_prog_type.get_type().pointer()
+ progs = []
+ for _, slot in radixtree.for_each_slot(idr_rt):
+ prog = slot.dereference().cast(bpf_prog_ptr_type)
+ progs.append(prog)
+ # Subprogs are not registered in prog_idr, fetch them manually.
+ # func[0] is the current prog.
+ aux = prog["aux"]
+ func = aux["func"]
+ real_func_cnt = int(aux["real_func_cnt"])
+ for i in range(1, real_func_cnt):
+ progs.append(func[i])
+ return progs
+
+
+class ProgAddBreakpoint(gdb.Breakpoint):
+ def __init__(self, monitor):
+ super(ProgAddBreakpoint, self).__init__("bpf_prog_kallsyms_add",
+ internal=True)
+ self.silent = True
+ self.monitor = monitor
+
+ def stop(self):
+ self.monitor.add(gdb.parse_and_eval("fp"))
+ return False
+
+
+class ProgRemoveBreakpoint(gdb.Breakpoint):
+ def __init__(self, monitor):
+ super(ProgRemoveBreakpoint, self).__init__("bpf_prog_free_id",
+ internal=True)
+ self.silent = True
+ self.monitor = monitor
+
+ def stop(self):
+ self.monitor.remove(gdb.parse_and_eval("prog"))
+ return False
+
+
+class ProgMonitor:
+ def __init__(self, add, remove):
+ self.add = add
+ self.remove = remove
+
+ self.add_bp = ProgAddBreakpoint(self)
+ self.remove_bp = ProgRemoveBreakpoint(self)
+
+ self.notify_initial()
+
+ def notify_initial(self):
+ for prog in list_progs():
+ self.add(prog)
+
+ def delete(self):
+ self.add_bp.delete()
+ self.remove_bp.delete()
+
+
+def btf_str_by_offset(btf, offset):
+ while offset < btf["start_str_off"]:
+ btf = btf["base_btf"]
+
+ offset -= btf["start_str_off"]
+ if offset < btf["hdr"]["str_len"]:
+ return (btf["strings"] + offset).string()
+
+ return None
+
+
+def bpf_line_info_line_num(line_col):
+ return line_col >> 10
+
+
+def bpf_line_info_line_col(line_col):
+ return line_col & 0x3ff
+
+
+class LInfoIter:
+ def __init__(self, prog):
+ # See bpf_prog_get_file_line() for details.
+ self.pos = 0
+ self.nr_linfo = 0
+
+ if prog is None:
+ return
+
+ self.bpf_func = int(prog["bpf_func"])
+ aux = prog["aux"]
+ self.btf = aux["btf"]
+ linfo_idx = aux["linfo_idx"]
+ self.nr_linfo = int(aux["nr_linfo"]) - linfo_idx
+ if self.nr_linfo == 0:
+ return
+
+ linfo_ptr = aux["linfo"]
+ tpe = linfo_ptr.type.target().array(self.nr_linfo).pointer()
+ self.linfo = (linfo_ptr + linfo_idx).cast(tpe).dereference()
+ jited_linfo_ptr = aux["jited_linfo"]
+ tpe = jited_linfo_ptr.type.target().array(self.nr_linfo).pointer()
+ self.jited_linfo = (jited_linfo_ptr + linfo_idx).cast(tpe).dereference()
+
+ self.filenos = {}
+
+ def get_code_off(self):
+ if self.pos >= self.nr_linfo:
+ return -1
+ return self.jited_linfo[self.pos] - self.bpf_func
+
+ def advance(self):
+ self.pos += 1
+
+ def get_fileno(self):
+ file_name_off = int(self.linfo[self.pos]["file_name_off"])
+ fileno = self.filenos.get(file_name_off)
+ if fileno is not None:
+ return fileno, None
+ file_name = btf_str_by_offset(self.btf, file_name_off)
+ fileno = len(self.filenos) + 1
+ self.filenos[file_name_off] = fileno
+ return fileno, file_name
+
+ def get_line_col(self):
+ line_col = int(self.linfo[self.pos]["line_col"])
+ return bpf_line_info_line_num(line_col), \
+ bpf_line_info_line_col(line_col)
+
+
+def generate_debug_obj(ksym, prog):
+ name = get_ksym_name(ksym)
+ # Avoid read_memory(); it throws bogus gdb.MemoryError in some contexts.
+ start = ksym["start"]
+ code = start.cast(gdb.lookup_type("unsigned char")
+ .array(int(ksym["end"]) - int(start))
+ .pointer()).dereference().bytes
+ linfo_iter = LInfoIter(prog)
+
+ result = tempfile.NamedTemporaryFile(suffix=".o", mode="wb")
+ try:
+ with tempfile.NamedTemporaryFile(suffix=".s", mode="w") as src:
+ # ".loc" does not apply to ".byte"s, only to ".insn"s, but since
+ # this needs to work for all architectures, the latter are not an
+ # option. Ask the assembler to apply ".loc"s to labels as well,
+ # and generate dummy labels after each ".loc".
+ src.write(".loc_mark_labels 1\n")
+
+ src.write(".globl {}\n".format(name))
+ src.write(".type {},@function\n".format(name))
+ src.write("{}:\n".format(name))
+ for code_off, code_byte in enumerate(code):
+ if linfo_iter.get_code_off() == code_off:
+ fileno, file_name = linfo_iter.get_fileno()
+ if file_name is not None:
+ src.write(".file {} {}\n".format(
+ fileno, json.dumps(file_name)))
+ line, col = linfo_iter.get_line_col()
+ src.write(".loc {} {} {}\n".format(fileno, line, col))
+ src.write("0:\n")
+ linfo_iter.advance()
+ src.write(".byte {}\n".format(code_byte))
+ src.write(".size {},{}\n".format(name, len(code)))
+ src.flush()
+
+ try:
+ subprocess.check_call(["as", "-c", src.name, "-o", result.name])
+ except FileNotFoundError:
+ # "as" is not installed.
+ result.close()
+ return None
+ return result
+ except:
+ result.close()
+ raise
diff --git a/scripts/gdb/linux/constants.py.in b/scripts/gdb/linux/constants.py.in
index d5e3069f42a7..5e294840b88d 100644
--- a/scripts/gdb/linux/constants.py.in
+++ b/scripts/gdb/linux/constants.py.in
@@ -163,3 +163,6 @@ LX_CONFIG(CONFIG_PAGE_OWNER)
LX_CONFIG(CONFIG_SLUB_DEBUG)
LX_CONFIG(CONFIG_SLAB_FREELIST_HARDENED)
LX_CONFIG(CONFIG_MMU)
+LX_CONFIG(CONFIG_BPF)
+LX_CONFIG(CONFIG_BPF_JIT)
+LX_CONFIG(CONFIG_BPF_SYSCALL)
diff --git a/scripts/gdb/linux/symbols.py b/scripts/gdb/linux/symbols.py
index 2332bd8eddf1..e69a02551ab7 100644
--- a/scripts/gdb/linux/symbols.py
+++ b/scripts/gdb/linux/symbols.py
@@ -11,13 +11,14 @@
# This work is licensed under the terms of the GNU GPL version 2.
#
+import atexit
import gdb
import os
import re
import struct
from itertools import count
-from linux import modules, utils, constants
+from linux import bpf, constants, modules, utils
if hasattr(gdb, 'Breakpoint'):
@@ -97,10 +98,17 @@ lx-symbols command."""
module_files_updated = False
loaded_modules = []
breakpoint = None
+ bpf_prog_monitor = None
+ bpf_ksym_monitor = None
+ bpf_progs = {}
+ # The remove-symbol-file command, even when invoked with -a, requires the
+ # respective object file to exist, so keep them around.
+ bpf_debug_objs = {}
def __init__(self):
super(LxSymbols, self).__init__("lx-symbols", gdb.COMMAND_FILES,
gdb.COMPLETE_FILENAME)
+ atexit.register(self.cleanup_bpf)
def _update_module_files(self):
self.module_files = []
@@ -173,6 +181,51 @@ lx-symbols command."""
else:
gdb.write("no module object found for '{0}'\n".format(module_name))
+ def add_bpf_prog(self, prog):
+ if prog["jited"]:
+ self.bpf_progs[int(prog["bpf_func"])] = prog
+
+ def remove_bpf_prog(self, prog):
+ self.bpf_progs.pop(int(prog["bpf_func"]), None)
+
+ def add_bpf_ksym(self, ksym):
+ addr = int(ksym["start"])
+ name = bpf.get_ksym_name(ksym)
+ with utils.pagination_off():
+ gdb.write("loading @{addr}: {name}\n".format(
+ addr=hex(addr), name=name))
+ debug_obj = bpf.generate_debug_obj(ksym, self.bpf_progs.get(addr))
+ if debug_obj is None:
+ return
+ try:
+ cmdline = "add-symbol-file {obj} {addr}".format(
+ obj=debug_obj.name, addr=hex(addr))
+ gdb.execute(cmdline, to_string=True)
+ except:
+ debug_obj.close()
+ raise
+ self.bpf_debug_objs[addr] = debug_obj
+
+ def remove_bpf_ksym(self, ksym):
+ addr = int(ksym["start"])
+ debug_obj = self.bpf_debug_objs.pop(addr, None)
+ if debug_obj is None:
+ return
+ try:
+ name = bpf.get_ksym_name(ksym)
+ gdb.write("unloading @{addr}: {name}\n".format(
+ addr=hex(addr), name=name))
+ cmdline = "remove-symbol-file {path}".format(path=debug_obj.name)
+ gdb.execute(cmdline, to_string=True)
+ finally:
+ debug_obj.close()
+
+ def cleanup_bpf(self):
+ self.bpf_progs = {}
+ while len(self.bpf_debug_objs) > 0:
+ self.bpf_debug_objs.popitem()[1].close()
+
+
def load_all_symbols(self):
gdb.write("loading vmlinux\n")
@@ -200,6 +253,12 @@ lx-symbols command."""
else:
[self.load_module_symbols(module) for module in module_list]
+ self.cleanup_bpf()
+ if self.bpf_prog_monitor is not None:
+ self.bpf_prog_monitor.notify_initial()
+ if self.bpf_ksym_monitor is not None:
+ self.bpf_ksym_monitor.notify_initial()
+
for saved_state in saved_states:
saved_state['breakpoint'].enabled = saved_state['enabled']
@@ -223,9 +282,21 @@ lx-symbols command."""
self.breakpoint = None
self.breakpoint = LoadModuleBreakpoint(
"kernel/module/main.c:do_init_module", self)
+ if self.bpf_prog_monitor is not None:
+ self.bpf_prog_monitor.delete()
+ self.bpf_prog_monitor = None
+ if constants.LX_CONFIG_BPF_SYSCALL:
+ self.bpf_prog_monitor = bpf.ProgMonitor(self.add_bpf_prog,
+ self.remove_bpf_prog)
+ if self.bpf_ksym_monitor is not None:
+ self.bpf_ksym_monitor.delete()
+ self.bpf_ksym_monitor = None
+ if constants.LX_CONFIG_BPF and constants.LX_CONFIG_BPF_JIT:
+ self.bpf_ksym_monitor = bpf.KsymMonitor(self.add_bpf_ksym,
+ self.remove_bpf_ksym)
else:
- gdb.write("Note: symbol update on module loading not supported "
- "with this gdb version\n")
+ gdb.write("Note: symbol update on module and BPF loading not "
+ "supported with this gdb version\n")
LxSymbols()
--
2.50.0
^ permalink raw reply related [flat|nested] 6+ messages in thread