On 2017-05-26 13:22, André Draszik wrote: > 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 > > Signed-off-by: André Draszik <[email protected]> > > --- > v3: pep8 compliant > v2: Commit message slightly updated > --- > 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 >
Acked-by: Jan Kiszka <[email protected]> Andrew, please include in your queue. Jan -- Siemens AG, Corporate Technology, CT RDA ITP SES-DE Corporate Competence Center Embedded Linux
