linux-kernel - Re: [PATCH v5 16/20] scripts/gdb: Add internal helper and convenience function for per-cpu lookup

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Date:	Tue, 29 Jan 2013 14:56:56 +0100
From:	Jan Kiszka <jan.kiszka@...mens.com>
To:	Borislav Petkov <bp@...en8.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org,
	Jason Wessel <jason.wessel@...driver.com>,
	kgdb-bugreport@...ts.sourceforge.net,
	Andi Kleen <andi@...stfloor.org>,
	Tom Tromey <tromey@...hat.com>,
	Ben Widawsky <ben@...dawsk.net>,
	"David S. Miller" <davem@...emloft.net>, sparclinux@...r.kernel.org
Subject: Re: [PATCH v5 16/20] scripts/gdb: Add internal helper and convenience
 function for per-cpu lookup

On 2013-01-29 14:51, Borislav Petkov wrote:
> On Tue, Jan 29, 2013 at 01:37:59PM +0100, Jan Kiszka wrote:
>> This function allows to obtain a per-cpu variable, either of the current
>> or an explicitly specified CPU.
>>
>> Note: sparc64 version is untested.
>>
>> CC: "David S. Miller" <davem@...emloft.net>
>> CC: sparclinux@...r.kernel.org
>> Signed-off-by: Jan Kiszka <jan.kiszka@...mens.com>
>> ---
>>  scripts/gdb/percpu.py      |   61 ++++++++++++++++++++++++++++++++++++++++++++
>>  scripts/gdb/vmlinux-gdb.py |    1 +
>>  2 files changed, 62 insertions(+), 0 deletions(-)
>>  create mode 100644 scripts/gdb/percpu.py
>>
>> diff --git a/scripts/gdb/percpu.py b/scripts/gdb/percpu.py
>> new file mode 100644
>> index 0000000..864962c
>> --- /dev/null
>> +++ b/scripts/gdb/percpu.py
>> @@ -0,0 +1,61 @@
>> +#
>> +# gdb helper commands and functions for Linux kernel debugging
>> +#
>> +#  per-cpu tools
> 
> This is actually a very cool thing for CPU guys: it can show what kind
> of hybrid CPUs they've been glueing together, like the following, for
> example:
> 
> ...
> (gdb) p $lx_per_cpu("cpu_info").x86_virt_bits
> $5 = 48 '0'
> (gdb) p $lx_per_cpu("cpu_info").x86_vendor_id
> $6 = "GenuineIntel\000\000\000"
> (gdb) p $lx_per_cpu("cpu_info").x86_model_id
> $7 = "AMD Phenom(tm) 9550 Quad-Core Processor", '\000' <repeats 24 times>
> (gdb)
> 
> Since when does Intel produce CPUs called "AMD Phenom(tm) 9550 Quad-Core
> Processor"? .. hahaha..

Let me guess: You are dumping a weird QEMU/KVM CPU, right?

> 
>> +#
>> +# Copyright (c) Siemens AG, 2011-2013
>> +#
>> +# Authors:
>> +#  Jan Kiszka <jan.kiszka@...mens.com>
>> +#
>> +# This work is licensed under the terms of the GNU GPL version 2.
>> +#
>> +
>> +import gdb
>> +
>> +from utils import *
>> +from task import *
>> +
>> +MAX_CPUS = 4096
>> +
>> +def get_current_cpu():
>> +	if get_gdbserver_type() == GDBSERVER_QEMU:
>> +		return gdb.selected_thread().num - 1
>> +	elif get_gdbserver_type() == GDBSERVER_KGDB:
>> +		tid = gdb.selected_thread().ptid[2]
>> +		if tid > (0x100000000 - MAX_CPUS - 2):
>> +			return 0x100000000 - tid - 2
>> +		else:
>> +			return get_thread_info(get_task_by_pid(tid))['cpu']
>> +	else:
>> +		raise gdb.GdbError("Sorry, obtaining the current CPU is "
>> +				   "not yet supported with this gdb server.")
>> +
>> +def per_cpu(var_ptr, cpu):
>> +	if cpu == -1:
>> +		cpu = get_current_cpu()
>> +	if is_target_arch("sparc:v9"):
>> +		offset = gdb.parse_and_eval("trap_block[" + str(cpu) +
>> +					    "].__per_cpu_base")
>> +	else:
>> +		offset = gdb.parse_and_eval("__per_cpu_offset[" + str(cpu) +
>> +					    "]")
>> +	pointer = var_ptr.cast(get_long_type()) + offset
>> +	return pointer.cast(var_ptr.type).dereference()
>> +
>> +
>> +class PerCpu(gdb.Function):
>> +	__doc__ = "Return per-cpu variable.\n" \
>> +		  "\n" \
>> +		  "$lx_per_cpu(\"VAR\"[, CPU]): Return the per-cpu variable called VAR for the\n" \
>> +		  "given CPU number. If CPU is omitted, the CPU of the current context is used.\n" \
>> +		  "Note that VAR has to be quoted as string."
> 
> 
> Ok, seriously now:
> 
> apropos shows the "Return per-cpu... " line above. Have you found out
> which gdb command shows the rest? help and info both say "Undefined
> command".

help function lx_...

It took me a while to find this, too.

Jan

-- 
Siemens AG, Corporate Technology, CT RTC ITP SDP-DE
Corporate Competence Center Embedded Linux
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