Commit deaee270 authored by John Ogness's avatar John Ogness Committed by Petr Mladek
Browse files

scripts/gdb: lx-dmesg: read records individually 



For the gdb command lx-dmesg, the entire descriptor, info, and text
data regions are read into memory before printing any records. For
large kernel log buffers, this not only causes a huge delay before
seeing any records, but it may also lead to python errors of too
much memory allocation.

Rather than reading in all these regions in advance, read them as
needed and only read the regions for the particular record that is
being printed.

The gdb macro "dmesg" in Documentation/admin-guide/kdump/gdbmacros.txt
already prints out the kernel log buffer like this.

Signed-off-by: default avatarJohn Ogness <john.ogness@linutronix.de>
Signed-off-by: default avatarPetr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/874k79c3a9.fsf@jogness.linutronix.de
parent 52e68cd6

scripts/gdb/linux/dmesg.py

+18 −17
Original line number Diff line number Diff line
@@ -44,19 +44,17 @@ class LxDmesg(gdb.Command): 
        sz = prb_desc_ring_type.get_type().sizeof

        desc_ring = utils.read_memoryview(inf, addr, sz).tobytes()



        # read in descriptor array

        # read in descriptor count, size, and address

        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()

        desc_addr = utils.read_ulong(desc_ring, off)



        # read in info array

        # read in info size and address

        info_sz = printk_info_type.get_type().sizeof

        off = prb_desc_ring_type.get_type()['infos'].bitpos // 8

        addr = utils.read_ulong(desc_ring, off)

        infos = utils.read_memoryview(inf, addr, info_sz * desc_ring_count).tobytes()

        info_addr = utils.read_ulong(desc_ring, off)



        # read in text data ring structure

        off = printk_ringbuffer_type.get_type()['text_data_ring'].bitpos // 8
@@ -64,12 +62,11 @@ class LxDmesg(gdb.Command): 
        sz = prb_data_ring_type.get_type().sizeof

        text_data_ring = utils.read_memoryview(inf, addr, sz).tobytes()



        # read in text data

        # read in text data size and address

        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()

        text_data_addr = utils.read_ulong(text_data_ring, off)



        counter_off = atomic_long_type.get_type()['counter'].bitpos // 8
@@ -102,17 +99,20 @@ class LxDmesg(gdb.Command): 
            desc_off = desc_sz * ind

            info_off = info_sz * ind



            desc = utils.read_memoryview(inf, desc_addr + desc_off, desc_sz).tobytes()



            # skip non-committed record

            state = 3 & (utils.read_u64(descs, desc_off + sv_off +

                                        counter_off) >> desc_flags_shift)

            state = 3 & (utils.read_u64(desc, sv_off + counter_off) >> desc_flags_shift)

            if state != desc_committed and state != desc_finalized:

                if did == head_id:

                    break

                did = (did + 1) & desc_id_mask

                continue



            begin = utils.read_ulong(descs, desc_off + begin_off) % text_data_sz

            end = utils.read_ulong(descs, desc_off + next_off) % text_data_sz

            begin = utils.read_ulong(desc, begin_off) % text_data_sz

            end = utils.read_ulong(desc, next_off) % text_data_sz



            info = utils.read_memoryview(inf, info_addr + info_off, info_sz).tobytes()



            # handle data-less record

            if begin & 1 == 1:
@@ -125,16 +125,17 @@ class LxDmesg(gdb.Command): 
                # skip over descriptor id

                text_start = begin + utils.get_long_type().sizeof



                text_len = utils.read_u16(infos, info_off + len_off)

                text_len = utils.read_u16(info, 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')

                text_data = utils.read_memoryview(inf, text_data_addr + text_start,

                                                  text_len).tobytes()

                text = text_data[0:text_len].decode(encoding='utf8', errors='replace')



            time_stamp = utils.read_u64(infos, info_off + ts_off)

            time_stamp = utils.read_u64(info, ts_off)



            for line in text.splitlines():

                msg = u"[{time:12.6f}] {line}\n".format(