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

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Date:   Fri, 17 Jun 2022 16:37:58 +0200
From:   Antonio Borneo <antonio.borneo@...s.st.com>
To:     Jan Kiszka <jan.kiszka@...mens.com>,
        Kieran Bingham <kbingham@...nel.org>,
        John Ogness <john.ogness@...utronix.de>,
        Petr Mladek <pmladek@...e.com>
CC:     Antonio Borneo <antonio.borneo@...s.st.com>,
        <linux-kernel@...r.kernel.org>,
        <linux-stm32@...md-mailman.stormreply.com>
Subject: [PATCH] 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

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@...s.st.com>
---
 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