From: "André Draszik" <git@andred.net>
To: linux-kernel@vger.kernel.org
Cc: Jan Kiszka <jan.kiszka@siemens.com>,
Kieran Bingham <kieran@ksquared.org.uk>
Subject: [PATCH] scripts/gdb: make lx-dmesg command work (reliably)
Date: Fri, 26 May 2017 12:04:54 +0100 [thread overview]
Message-ID: <20170526110454.1119-1-git@andred.net> (raw)
lx-dmesg needs access to the log_buf symbol from printk.c.
Unfortunately, the symbol log_buf also exists in BPF's
verifier.c and hence gdb can pick one or the other. If it
happens to pick BPF's log_buf, lx-dmesg doesn't work:
(gdb) lx-dmesg
Python Exception <class 'gdb.MemoryError'> Cannot access memory at address 0x0:
Error occurred in Python command: Cannot access memory at address 0x0
(gdb) p log_buf
$15 = 0x0
Luckily, GDB has a way to deal with this, see
https://sourceware.org/gdb/onlinedocs/gdb/Symbols.html
(gdb) info variables ^log_buf$
All variables matching regular expression "^log_buf$":
File <linux.git>/kernel/bpf/verifier.c:
static char *log_buf;
File <linux.git>/kernel/printk/printk.c:
static char *log_buf;
(gdb) p 'verifier.c'::log_buf
$1 = 0x0
(gdb) p 'printk.c'::log_buf
$2 = 0x811a6aa0 <__log_buf> ""
By being explicit about the location of the symbol, we
can make lx-dmesg work again. While at it, do the same
for the other symbols we need from printk.c
Signed-off-by: André Draszik <git@andred.net>
---
scripts/gdb/linux/dmesg.py | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)
diff --git a/scripts/gdb/linux/dmesg.py b/scripts/gdb/linux/dmesg.py
index f9b92ece7834..11f2397d40ed 100644
--- a/scripts/gdb/linux/dmesg.py
+++ b/scripts/gdb/linux/dmesg.py
@@ -23,10 +23,10 @@ class LxDmesg(gdb.Command):
super(LxDmesg, self).__init__("lx-dmesg", gdb.COMMAND_DATA)
def invoke(self, arg, from_tty):
- log_buf_addr = int(str(gdb.parse_and_eval("log_buf")).split()[0], 16)
- log_first_idx = int(gdb.parse_and_eval("log_first_idx"))
- log_next_idx = int(gdb.parse_and_eval("log_next_idx"))
- log_buf_len = int(gdb.parse_and_eval("log_buf_len"))
+ log_buf_addr = int(str(gdb.parse_and_eval("'printk.c'::log_buf")).split()[0], 16)
+ log_first_idx = int(gdb.parse_and_eval("'printk.c'::log_first_idx"))
+ log_next_idx = int(gdb.parse_and_eval("'printk.c'::log_next_idx"))
+ log_buf_len = int(gdb.parse_and_eval("'printk.c'::log_buf_len"))
inf = gdb.inferiors()[0]
start = log_buf_addr + log_first_idx
--
2.11.0
next reply other threads:[~2017-05-26 11:05 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-05-26 11:04 André Draszik [this message]
2017-05-26 11:12 ` [PATCH] scripts/gdb: make lx-dmesg command work (reliably) Jan Kiszka
2017-05-27 14:01 ` Andy Shevchenko
2017-05-28 16:29 ` Jan Kiszka
2017-05-26 11:13 ` [PATCH v2] " André Draszik
2017-05-26 11:22 ` [PATCH v3] " André Draszik
2017-05-26 11:28 ` Jan Kiszka
2017-05-31 5:10 ` Kieran Bingham
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