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

From: Antonio Borneo
Date: Fri Jun 17 2022 - 10:38:53 EST


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

Use the existing utils.read_ulong() to read 'counter' inside the
atomic_long_t.

Fixes: e60768311af8 ("scripts/gdb: update for lockless printk ringbuffer")
Signed-off-by: Antonio Borneo <antonio.borneo@xxxxxxxxxxx>
---
scripts/gdb/linux/dmesg.py | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/scripts/gdb/linux/dmesg.py b/scripts/gdb/linux/dmesg.py
index d5983cf3db7d..e2d9ab3aa836 100644
--- a/scripts/gdb/linux/dmesg.py
+++ b/scripts/gdb/linux/dmesg.py
@@ -89,9 +89,9 @@ 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_ulong(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)
+ head_id = utils.read_ulong(desc_ring, off + counter_off)

did = tail_id
while True:
@@ -102,7 +102,7 @@ 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_ulong(desc, sv_off + counter_off) >> desc_flags_shift)
if state != desc_committed and state != desc_finalized:
if did == head_id:
break

base-commit: b13baccc3850ca8b8cccbf8ed9912dbaa0fdf7f3
--
2.36.1