Documentation / kdump / gdbmacros.txt

Based on kernel version 4.16.1. Page generated on 2018-04-09 11:53 EST.

	#
	# 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_log_idx
		set $idx = $arg0
		if ($argc > 1)
			set $prev_flags = $arg1
		else
			set $prev_flags = 0
		end
		set $msg = ((struct printk_log *) (log_buf + $idx))
		set $prefix = 1
		set $newline = 1
		set $log = log_buf + $idx + sizeof(*$msg)
	
		# prev & LOG_CONT && !(msg->flags & LOG_PREIX)
		if (($prev_flags & 8) && !($msg->flags & 4))
			set $prefix = 0
		end
	
		# msg->flags & LOG_CONT
		if ($msg->flags & 8)
			# (prev & LOG_CONT && !(prev & LOG_NEWLINE))
			if (($prev_flags & 8) && !($prev_flags & 2))
				set $prefix = 0
			end
			# (!(msg->flags & LOG_NEWLINE))
			if (!($msg->flags & 2))
				set $newline = 0
			end
		end
	
		if ($prefix)
			printf "[%5lu.%06lu] ", $msg->ts_nsec / 1000000000, $msg->ts_nsec % 1000000000
		end
		if ($msg->text_len != 0)
			eval "printf \"%%%d.%ds\", $log", $msg->text_len, $msg->text_len
		end
		if ($newline)
			printf "\n"
		end
		if ($msg->dict_len > 0)
			set $dict = $log + $msg->text_len
			set $idx = 0
			set $line = 1
			while ($idx < $msg->dict_len)
				if ($line)
					printf " "
					set $line = 0
				end
				set $c = $dict[$idx]
				if ($c == '\0')
					printf "\n"
					set $line = 1
				else
					if ($c < ' ' || $c >= 127 || $c == '\\')
						printf "\\x%02x", $c
					else
						printf "%c", $c
					end
				end
				set $idx = $idx + 1
			end
			printf "\n"
		end
	end
	document dump_log_idx
		Dump a single log given its index in the log buffer.  The first
		parameter is the index into log_buf, the second is optional and
		specified the previous log buffer's flags, used for properly
		formatting continued lines.
	end
	
	define dmesg
		set $i = log_first_idx
		set $end_idx = log_first_idx
		set $prev_flags = 0
	
		while (1)
			set $msg = ((struct printk_log *) (log_buf + $i))
			if ($msg->len == 0)
				set $i = 0
			else
				dump_log_idx $i $prev_flags
				set $i = $i + $msg->len
				set $prev_flags = $msg->flags
			end
			if ($i == $end_idx)
				loop_break
			end
		end
	end
	document dmesg
		print the kernel ring buffer
	end

• [ kdump ]
• gdbmacros.txt
• kdump.txt
•  

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