Commit e3c8d33e authored by Antonio Borneo's avatar Antonio Borneo Committed by Petr Mladek
Browse files

scripts/gdb: fix 'lx-dmesg' on 32 bits arch 

The type atomic_long_t can have size 4 or 8 bytes, depending on
CONFIG_64BIT; it's only content, the field 'counter', is either an
int or a s64 value.

Current code incorrectly uses the fixed size utils.read_u64() to
read the field 'counter' inside atomic_long_t.

On 32 bits architectures reading the last element 'tail_id' of the
struct prb_desc_ring:
	struct prb_desc_ring {
		...
		atomic_long_t tail_id;
	};
causes the utils.read_u64() to access outside the boundary of the
struct and the gdb command 'lx-dmesg' exits with error:
	Python Exception <class 'IndexError'>: index out of range
	Error occurred in Python: index out of range

Query the really used atomic_long_t counter type size.

Link: https://lore.kernel.org/r/20220617143758.137307-1-antonio.borneo@foss.st.com


Fixes: e6076831 ("scripts/gdb: update for lockless printk ringbuffer")
Signed-off-by: default avatarAntonio Borneo <antonio.borneo@foss.st.com>
[pmladek@suse.com: Query the really used atomic_long_t counter type size]
Tested-by: default avatarAntonio Borneo <antonio.borneo@foss.st.com>
Reviewed-by: default avatarJohn Ogness <john.ogness@linutronix.de>
Signed-off-by: default avatarPetr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20220719122831.19890-1-pmladek@suse.com
parent 9a3bfa01

scripts/gdb/linux/dmesg.py

+3 −6
Original line number Diff line number Diff line
@@ -22,7 +22,6 @@ 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."""
@@ -68,8 +67,6 @@ class LxDmesg(gdb.Command): 
        off = prb_data_ring_type.get_type()['data'].bitpos // 8

        text_data_addr = utils.read_ulong(text_data_ring, off)



        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
@@ -89,9 +86,9 @@ class LxDmesg(gdb.Command): 


        # 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)

        tail_id = utils.read_atomic_long(desc_ring, off)

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

        head_id = utils.read_u64(desc_ring, off + counter_off)

        head_id = utils.read_atomic_long(desc_ring, off)



        did = tail_id

        while True:
@@ -102,7 +99,7 @@ class LxDmesg(gdb.Command): 
            desc = utils.read_memoryview(inf, desc_addr + desc_off, desc_sz).tobytes()



            # skip non-committed record

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

            state = 3 & (utils.read_atomic_long(desc, sv_off) >> desc_flags_shift)

            if state != desc_committed and state != desc_finalized:

                if did == head_id:

                    break

scripts/gdb/linux/utils.py

+12 −2
Original line number Diff line number Diff line
@@ -35,13 +35,12 @@ class CachedType: 




long_type = CachedType("long")



atomic_long_type = CachedType("atomic_long_t")



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)
@@ -129,6 +128,17 @@ def read_ulong(buffer, offset): 
    else:

        return read_u32(buffer, offset)



atomic_long_counter_offset = atomic_long_type.get_type()['counter'].bitpos

atomic_long_counter_sizeof = atomic_long_type.get_type()['counter'].type.sizeof



def read_atomic_long(buffer, offset):

    global atomic_long_counter_offset

    global atomic_long_counter_sizeof



    if atomic_long_counter_sizeof == 8:

        return read_u64(buffer, offset + atomic_long_counter_offset)

    else:

        return read_u32(buffer, offset + atomic_long_counter_offset)



target_arch = None