From: André Draszik git@andred.net

commit d6c9708737c2107c38bd75f133d14d5801b8d6d5 upstream

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> "" (gdb) p &log_buf $3 = (char **) 0x8120fe40 <log_buf> (gdb) p &'verifier.c'::log_buf $4 = (char **) 0x8120fe40 <log_buf> (gdb) p &'printk.c'::log_buf $5 = (char **) 0x8048b7d0 <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

Link: http://lkml.kernel.org/r/20170526112222.3414-1-git@andred.net Signed-off-by: André Draszik git@andred.net Tested-by: Kieran Bingham kieran@bingham.xyz Acked-by: Jan Kiszka jan.kiszka@siemens.com Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Linus Torvalds torvalds@linux-foundation.org Signed-off-by: Florian Fainelli f.fainelli@gmail.com --- scripts/gdb/linux/dmesg.py | 9 +++++---- 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/scripts/gdb/linux/dmesg.py b/scripts/gdb/linux/dmesg.py index f9b92ece7834..5afd1098e33a 100644 --- a/scripts/gdb/linux/dmesg.py +++ b/scripts/gdb/linux/dmesg.py @@ -23,10 +23,11 @@ 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

From: Leonard Crestez leonard.crestez@nxp.com

commit 46d10a094353c05144f3b0530516bdac3ce7c435 upstream

Use errors=replace because it is never desirable for lx-dmesg to fail on string decoding errors, not even if the log buffer is corrupt and we show incorrect info.

The kernel will sometimes print utf8, for example the copyright symbol from jffs2. In order to make this work specify 'utf8' everywhere because python2 otherwise defaults to 'ascii'.

In theory the second errors='replace' is not be required because everything that can be decoded as utf8 should also be encodable back to utf8. But it's better to be extra safe here. It's worth noting that this is definitely not true for encoding='ascii', unknown characters are replaced with U+FFFD REPLACEMENT CHARACTER and they fail to encode back to ascii.

Link: http://lkml.kernel.org/r/acee067f3345954ed41efb77b80eebdc038619c6.1498481469... Signed-off-by: Leonard Crestez leonard.crestez@nxp.com Acked-by: Jan Kiszka jan.kiszka@siemens.com Cc: Jason Wessel jason.wessel@windriver.com Cc: Kieran Bingham kieran@ksquared.org.uk Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Linus Torvalds torvalds@linux-foundation.org Signed-off-by: Florian Fainelli f.fainelli@gmail.com --- scripts/gdb/linux/dmesg.py | 13 ++++++++++--- 1 file changed, 10 insertions(+), 3 deletions(-)

diff --git a/scripts/gdb/linux/dmesg.py b/scripts/gdb/linux/dmesg.py index f5a030333dfd..6d2e09a2ad2f 100644 --- a/scripts/gdb/linux/dmesg.py +++ b/scripts/gdb/linux/dmesg.py @@ -12,6 +12,7 @@ #

import gdb +import sys

from linux import utils

@@ -52,13 +53,19 @@ class LxDmesg(gdb.Command): continue

text_len = utils.read_u16(log_buf[pos + 10:pos + 12]) - text = log_buf[pos + 16:pos + 16 + text_len].decode() + text = log_buf[pos + 16:pos + 16 + text_len].decode( + encoding='utf8', errors='replace') time_stamp = utils.read_u64(log_buf[pos:pos + 8])

for line in text.splitlines(): - gdb.write("[{time:12.6f}] {line}\n".format( + msg = u"[{time:12.6f}] {line}\n".format( time=time_stamp / 1000000000.0, - line=line)) + line=line) + # With python2 gdb.write will attempt to convert unicode to + # ascii and might fail so pass an utf8-encoded str instead. + if sys.hexversion < 0x03000000: + msg = msg.encode(encoding='utf8', errors='replace') + gdb.write(msg)

pos += length