Documentation/admin-guide/kdump/gdbmacros.txt

#
# This file contains a few gdb macros (user defined commands) to extract
# useful information from kernel crashdump (kdump) like stack traces of
# all the processes or a particular process and trapinfo.
#
# These macros can be used by copying this file in .gdbinit (put in home
# directory or current directory) or by invoking gdb command with
# --command=<command-file-name> option
#
# Credits:
# Alexander Nyberg <alexn@telia.com>
# V Srivatsa <vatsa@in.ibm.com>
# Maneesh Soni <maneesh@in.ibm.com>
#

define bttnobp
	set $tasks_off=((size_t)&((struct task_struct *)0)->tasks)
	set $pid_off=((size_t)&((struct task_struct *)0)->thread_group.next)
	set $init_t=&init_task
	set $next_t=(((char *)($init_t->tasks).next) - $tasks_off)
	set var $stacksize = sizeof(union thread_union)
	while ($next_t != $init_t)
		set $next_t=(struct task_struct *)$next_t
		printf "\npid %d; comm %s:\n", $next_t.pid, $next_t.comm
		printf "===================\n"
		set var $stackp = $next_t.thread.sp
		set var $stack_top = ($stackp & ~($stacksize - 1)) + $stacksize

		while ($stackp < $stack_top)
			if (*($stackp) > _stext && *($stackp) < _sinittext)
				info symbol *($stackp)
			end
			set $stackp += 4
		end
		set $next_th=(((char *)$next_t->thread_group.next) - $pid_off)
		while ($next_th != $next_t)
			set $next_th=(struct task_struct *)$next_th
			printf "\npid %d; comm %s:\n", $next_t.pid, $next_t.comm
			printf "===================\n"
			set var $stackp = $next_t.thread.sp
			set var $stack_top = ($stackp & ~($stacksize - 1)) + stacksize

			while ($stackp < $stack_top)
				if (*($stackp) > _stext && *($stackp) < _sinittext)
					info symbol *($stackp)
				end
				set $stackp += 4
			end
			set $next_th=(((char *)$next_th->thread_group.next) - $pid_off)
		end
		set $next_t=(char *)($next_t->tasks.next) - $tasks_off
	end
end
document bttnobp
	dump all thread stack traces on a kernel compiled with !CONFIG_FRAME_POINTER
end

define btthreadstack
	set var $pid_task = $arg0

	printf "\npid %d; comm %s:\n", $pid_task.pid, $pid_task.comm
	printf "task struct: "
	print $pid_task
	printf "===================\n"
	set var $stackp = $pid_task.thread.sp
	set var $stacksize = sizeof(union thread_union)
	set var $stack_top = ($stackp & ~($stacksize - 1)) + $stacksize
	set var $stack_bot = ($stackp & ~($stacksize - 1))

	set $stackp = *((unsigned long *) $stackp)
	while (($stackp < $stack_top) && ($stackp > $stack_bot))
		set var $addr = *(((unsigned long *) $stackp) + 1)
		info symbol $addr
		set $stackp = *((unsigned long *) $stackp)
	end
end
document btthreadstack
	 dump a thread stack using the given task structure pointer
end


define btt
	set $tasks_off=((size_t)&((struct task_struct *)0)->tasks)
	set $pid_off=((size_t)&((struct task_struct *)0)->thread_group.next)
	set $init_t=&init_task
	set $next_t=(((char *)($init_t->tasks).next) - $tasks_off)
	while ($next_t != $init_t)
		set $next_t=(struct task_struct *)$next_t
		btthreadstack $next_t

		set $next_th=(((char *)$next_t->thread_group.next) - $pid_off)
		while ($next_th != $next_t)
			set $next_th=(struct task_struct *)$next_th
			btthreadstack $next_th
			set $next_th=(((char *)$next_th->thread_group.next) - $pid_off)
		end
		set $next_t=(char *)($next_t->tasks.next) - $tasks_off
	end
end
document btt
	dump all thread stack traces on a kernel compiled with CONFIG_FRAME_POINTER
end

define btpid
	set var $pid = $arg0
	set $tasks_off=((size_t)&((struct task_struct *)0)->tasks)
	set $pid_off=((size_t)&((struct task_struct *)0)->thread_group.next)
	set $init_t=&init_task
	set $next_t=(((char *)($init_t->tasks).next) - $tasks_off)
	set var $pid_task = 0

	while ($next_t != $init_t)
		set $next_t=(struct task_struct *)$next_t

		if ($next_t.pid == $pid)
			set $pid_task = $next_t
		end

		set $next_th=(((char *)$next_t->thread_group.next) - $pid_off)
		while ($next_th != $next_t)
			set $next_th=(struct task_struct *)$next_th
			if ($next_th.pid == $pid)
				set $pid_task = $next_th
			end
			set $next_th=(((char *)$next_th->thread_group.next) - $pid_off)
		end
		set $next_t=(char *)($next_t->tasks.next) - $tasks_off
	end

	btthreadstack $pid_task
end
document btpid
	backtrace of pid
end


define trapinfo
	set var $pid = $arg0
	set $tasks_off=((size_t)&((struct task_struct *)0)->tasks)
	set $pid_off=((size_t)&((struct task_struct *)0)->thread_group.next)
	set $init_t=&init_task
	set $next_t=(((char *)($init_t->tasks).next) - $tasks_off)
	set var $pid_task = 0

	while ($next_t != $init_t)
		set $next_t=(struct task_struct *)$next_t

		if ($next_t.pid == $pid)
			set $pid_task = $next_t
		end

		set $next_th=(((char *)$next_t->thread_group.next) - $pid_off)
		while ($next_th != $next_t)
			set $next_th=(struct task_struct *)$next_th
			if ($next_th.pid == $pid)
				set $pid_task = $next_th
			end
			set $next_th=(((char *)$next_th->thread_group.next) - $pid_off)
		end
		set $next_t=(char *)($next_t->tasks.next) - $tasks_off
	end

	printf "Trapno %ld, cr2 0x%lx, error_code %ld\n", $pid_task.thread.trap_no, \
				$pid_task.thread.cr2, $pid_task.thread.error_code

end
document trapinfo
	Run info threads and lookup pid of thread #1
	'trapinfo <pid>' will tell you by which trap & possibly
	address the kernel panicked.
end

define dump_record
	set var $desc = $arg0
	set var $info = $arg1
	if ($argc > 2)
		set var $prev_flags = $arg2
	else
		set var $prev_flags = 0
	end

	set var $prefix = 1
	set var $newline = 1

	set var $begin = $desc->text_blk_lpos.begin % (1U << prb->text_data_ring.size_bits)
	set var $next = $desc->text_blk_lpos.next % (1U << prb->text_data_ring.size_bits)

	# handle data-less record
	if ($begin & 1)
		set var $text_len = 0
		set var $log = ""
	else
		# handle wrapping data block
		if ($begin > $next)
			set var $begin = 0
		end

		# skip over descriptor id
		set var $begin = $begin + sizeof(long)

		# handle truncated message
		if ($next - $begin < $info->text_len)
			set var $text_len = $next - $begin
		else
			set var $text_len = $info->text_len
		end

		set var $log = &prb->text_data_ring.data[$begin]
	end

	# prev & LOG_CONT && !(info->flags & LOG_PREIX)
	if (($prev_flags & 8) && !($info->flags & 4))
		set var $prefix = 0
	end

	# info->flags & LOG_CONT
	if ($info->flags & 8)
		# (prev & LOG_CONT && !(prev & LOG_NEWLINE))
		if (($prev_flags & 8) && !($prev_flags & 2))
			set var $prefix = 0
		end
		# (!(info->flags & LOG_NEWLINE))
		if (!($info->flags & 2))
			set var $newline = 0
		end
	end

	if ($prefix)
		printf "[%5lu.%06lu] ", $info->ts_nsec / 1000000000, $info->ts_nsec % 1000000000
	end
	if ($text_len)
		eval "printf \"%%%d.%ds\", $log", $text_len, $text_len
	end
	if ($newline)
		printf "\n"
	end

	# handle dictionary data

	set var $dict = &$info->dev_info.subsystem[0]
	set var $dict_len = sizeof($info->dev_info.subsystem)
	if ($dict[0] != '\0')
		printf " SUBSYSTEM="
		set var $idx = 0
		while ($idx < $dict_len)
			set var $c = $dict[$idx]
			if ($c == '\0')
				loop_break
			else
				if ($c < ' ' || $c >= 127 || $c == '\\')
					printf "\\x%02x", $c
				else
					printf "%c", $c
				end
			end
			set var $idx = $idx + 1
		end
		printf "\n"
	end

	set var $dict = &$info->dev_info.device[0]
	set var $dict_len = sizeof($info->dev_info.device)
	if ($dict[0] != '\0')
		printf " DEVICE="
		set var $idx = 0
		while ($idx < $dict_len)
			set var $c = $dict[$idx]
			if ($c == '\0')
				loop_break
			else
				if ($c < ' ' || $c >= 127 || $c == '\\')
					printf "\\x%02x", $c
				else
					printf "%c", $c
				end
			end
			set var $idx = $idx + 1
		end
		printf "\n"
	end
end
document dump_record
	Dump a single record. The first parameter is the descriptor,
	the second parameter is the info, the third parameter is
	optional and specifies the previous record's flags, used for
	properly formatting continued lines.
end

define dmesg
	# definitions from kernel/printk/printk_ringbuffer.h
	set var $desc_committed = 1
	set var $desc_finalized = 2
	set var $desc_sv_bits = sizeof(long) * 8
	set var $desc_flags_shift = $desc_sv_bits - 2
	set var $desc_flags_mask = 3 << $desc_flags_shift
	set var $id_mask = ~$desc_flags_mask

	set var $desc_count = 1U << prb->desc_ring.count_bits
	set var $prev_flags = 0

	set var $id = prb->desc_ring.tail_id.counter
	set var $end_id = prb->desc_ring.head_id.counter

	while (1)
		set var $desc = &prb->desc_ring.descs[$id % $desc_count]
		set var $info = &prb->desc_ring.infos[$id % $desc_count]

		# skip non-committed record
		set var $state = 3 & ($desc->state_var.counter >> $desc_flags_shift)
		if ($state == $desc_committed || $state == $desc_finalized)
			dump_record $desc $info $prev_flags
			set var $prev_flags = $info->flags
		end

		if ($id == $end_id)
			loop_break
		end
		set var $id = ($id + 1) & $id_mask
	end
end
document dmesg
	print the kernel ring buffer
end