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    Subject[PATCH 5.15 522/779] scripts/gdb: fix lx-dmesg on 32 bits arch
    Date
    From: Antonio Borneo <antonio.borneo@foss.st.com>

    [ Upstream commit e3c8d33e0d62175c31ca7ab7ab01b18f0b6318d3 ]

    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: e60768311af8 ("scripts/gdb: update for lockless printk ringbuffer")
    Signed-off-by: Antonio Borneo <antonio.borneo@foss.st.com>
    [pmladek@suse.com: Query the really used atomic_long_t counter type size]
    Tested-by: Antonio Borneo <antonio.borneo@foss.st.com>
    Reviewed-by: John Ogness <john.ogness@linutronix.de>
    Signed-off-by: Petr Mladek <pmladek@suse.com>
    Link: https://lore.kernel.org/r/20220719122831.19890-1-pmladek@suse.com
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    scripts/gdb/linux/dmesg.py | 9 +++------
    scripts/gdb/linux/utils.py | 14 ++++++++++++--
    2 files changed, 15 insertions(+), 8 deletions(-)

    diff --git a/scripts/gdb/linux/dmesg.py b/scripts/gdb/linux/dmesg.py
    index d5983cf3db7d..c771831eb077 100644
    --- a/scripts/gdb/linux/dmesg.py
    +++ b/scripts/gdb/linux/dmesg.py
    @@ -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
    diff --git a/scripts/gdb/linux/utils.py b/scripts/gdb/linux/utils.py
    index ff7c1799d588..1553f68716cc 100644
    --- a/scripts/gdb/linux/utils.py
    +++ b/scripts/gdb/linux/utils.py
    @@ -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

    --
    2.35.1


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