scripts/gdb: update for lockless printk ringbuffer
With the introduction of the lockless printk ringbuffer, the data
structure for the kernel log buffer was changed. Update the gdb
scripts to be able to parse/print the new log buffer structure.
Fixes: 896fbe20b4e2333fb55 ("printk: use the lockless ringbuffer")
Signed-off-by: John Ogness <john.ogness@linutronix.de>
Reported-by: Nick Desaulniers <ndesaulniers@google.com>
Tested-by: Nick Desaulniers <ndesaulniers@google.com>
Tested-by: Petr Mladek <pmladek@suse.com>
[akpm@linux-foundation.org: A typo fix.]
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20200814212525.6118-3-john.ogness@linutronix.de
diff --git a/scripts/gdb/linux/dmesg.py b/scripts/gdb/linux/dmesg.py
index 2fa7bb8..6c60220 100644
--- a/scripts/gdb/linux/dmesg.py
+++ b/scripts/gdb/linux/dmesg.py
@@ -16,8 +16,13 @@
from linux import utils
-printk_log_type = utils.CachedType("struct printk_log")
-
+printk_info_type = utils.CachedType("struct printk_info")
+prb_data_blk_lpos_type = utils.CachedType("struct prb_data_blk_lpos")
+prb_desc_type = utils.CachedType("struct prb_desc")
+prb_desc_ring_type = utils.CachedType("struct prb_desc_ring")
+prb_data_ring_type = utils.CachedType("struct prb_data_ring")
+printk_ringbuffer_type = utils.CachedType("struct printk_ringbuffer")
+atomic_long_type = utils.CachedType("atomic_long_t")
class LxDmesg(gdb.Command):
"""Print Linux kernel log buffer."""
@@ -26,44 +31,102 @@
super(LxDmesg, self).__init__("lx-dmesg", gdb.COMMAND_DATA)
def invoke(self, arg, from_tty):
- log_buf_addr = int(str(gdb.parse_and_eval(
- "(void *)'printk.c'::log_buf")).split()[0], 16)
- log_first_idx = int(gdb.parse_and_eval("'printk.c'::log_first_idx"))
- log_next_idx = int(gdb.parse_and_eval("'printk.c'::log_next_idx"))
- log_buf_len = int(gdb.parse_and_eval("'printk.c'::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 = utils.read_memoryview(inf, start, length).tobytes()
- else:
- log_buf_2nd_half = log_buf_len - log_first_idx
- a = utils.read_memoryview(inf, start, log_buf_2nd_half)
- b = utils.read_memoryview(inf, log_buf_addr, log_next_idx)
- log_buf = a.tobytes() + b.tobytes()
- length_offset = printk_log_type.get_type()['len'].bitpos // 8
- text_len_offset = printk_log_type.get_type()['text_len'].bitpos // 8
- time_stamp_offset = printk_log_type.get_type()['ts_nsec'].bitpos // 8
- text_offset = printk_log_type.get_type().sizeof
+ # read in prb structure
+ prb_addr = int(str(gdb.parse_and_eval("(void *)'printk.c'::prb")).split()[0], 16)
+ sz = printk_ringbuffer_type.get_type().sizeof
+ prb = utils.read_memoryview(inf, prb_addr, sz).tobytes()
- pos = 0
- while pos < log_buf.__len__():
- length = utils.read_u16(log_buf, pos + length_offset)
- if length == 0:
- if log_buf_2nd_half == -1:
- gdb.write("Corrupted log buffer!\n")
+ # read in descriptor ring structure
+ off = printk_ringbuffer_type.get_type()['desc_ring'].bitpos // 8
+ addr = prb_addr + off
+ sz = prb_desc_ring_type.get_type().sizeof
+ desc_ring = utils.read_memoryview(inf, addr, sz).tobytes()
+
+ # read in descriptor array
+ off = prb_desc_ring_type.get_type()['count_bits'].bitpos // 8
+ desc_ring_count = 1 << utils.read_u32(desc_ring, off)
+ desc_sz = prb_desc_type.get_type().sizeof
+ off = prb_desc_ring_type.get_type()['descs'].bitpos // 8
+ addr = utils.read_ulong(desc_ring, off)
+ descs = utils.read_memoryview(inf, addr, desc_sz * desc_ring_count).tobytes()
+
+ # read in text data ring structure
+ off = printk_ringbuffer_type.get_type()['text_data_ring'].bitpos // 8
+ addr = prb_addr + off
+ sz = prb_data_ring_type.get_type().sizeof
+ text_data_ring = utils.read_memoryview(inf, addr, sz).tobytes()
+
+ # read in text data
+ off = prb_data_ring_type.get_type()['size_bits'].bitpos // 8
+ text_data_sz = 1 << utils.read_u32(text_data_ring, off)
+ off = prb_data_ring_type.get_type()['data'].bitpos // 8
+ addr = utils.read_ulong(text_data_ring, off)
+ text_data = utils.read_memoryview(inf, addr, text_data_sz).tobytes()
+
+ counter_off = atomic_long_type.get_type()['counter'].bitpos // 8
+
+ sv_off = prb_desc_type.get_type()['state_var'].bitpos // 8
+
+ off = prb_desc_type.get_type()['text_blk_lpos'].bitpos // 8
+ begin_off = off + (prb_data_blk_lpos_type.get_type()['begin'].bitpos // 8)
+ next_off = off + (prb_data_blk_lpos_type.get_type()['next'].bitpos // 8)
+
+ off = prb_desc_type.get_type()['info'].bitpos // 8
+ ts_off = off + printk_info_type.get_type()['ts_nsec'].bitpos // 8
+ len_off = off + printk_info_type.get_type()['text_len'].bitpos // 8
+
+ # definitions from kernel/printk/printk_ringbuffer.h
+ desc_sv_bits = utils.get_long_type().sizeof * 8
+ desc_committed_mask = 1 << (desc_sv_bits - 1)
+ desc_reuse_mask = 1 << (desc_sv_bits - 2)
+ desc_flags_mask = desc_committed_mask | desc_reuse_mask
+ desc_id_mask = ~desc_flags_mask
+
+ # read in tail and head descriptor ids
+ off = prb_desc_ring_type.get_type()['tail_id'].bitpos // 8
+ tail_id = utils.read_u64(desc_ring, off + counter_off)
+ off = prb_desc_ring_type.get_type()['head_id'].bitpos // 8
+ head_id = utils.read_u64(desc_ring, off + counter_off)
+
+ did = tail_id
+ while True:
+ ind = did % desc_ring_count
+ desc_off = desc_sz * ind
+
+ # skip non-committed record
+ state = utils.read_u64(descs, desc_off + sv_off + counter_off) & desc_flags_mask
+ if state != desc_committed_mask:
+ if did == head_id:
break
- pos = log_buf_2nd_half
+ did = (did + 1) & desc_id_mask
continue
- text_len = utils.read_u16(log_buf, pos + text_len_offset)
- text_start = pos + text_offset
- text = log_buf[text_start:text_start + text_len].decode(
- encoding='utf8', errors='replace')
- time_stamp = utils.read_u64(log_buf, pos + time_stamp_offset)
+ begin = utils.read_ulong(descs, desc_off + begin_off) % text_data_sz
+ end = utils.read_ulong(descs, desc_off + next_off) % text_data_sz
+
+ # handle data-less record
+ if begin & 1 == 1:
+ text = ""
+ else:
+ # handle wrapping data block
+ if begin > end:
+ begin = 0
+
+ # skip over descriptor id
+ text_start = begin + utils.get_long_type().sizeof
+
+ text_len = utils.read_u16(descs, desc_off + len_off)
+
+ # handle truncated message
+ if end - text_start < text_len:
+ text_len = end - text_start
+
+ text = text_data[text_start:text_start + text_len].decode(
+ encoding='utf8', errors='replace')
+
+ time_stamp = utils.read_u64(descs, desc_off + ts_off)
for line in text.splitlines():
msg = u"[{time:12.6f}] {line}\n".format(
@@ -75,7 +138,9 @@
msg = msg.encode(encoding='utf8', errors='replace')
gdb.write(msg)
- pos += length
+ if did == head_id:
+ break
+ did = (did + 1) & desc_id_mask
LxDmesg()