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201
Documentation/kdump/gdbmacros.txt
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201
Documentation/kdump/gdbmacros.txt
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#
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# This file contains a few gdb macros (user defined commands) to extract
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# useful information from kernel crashdump (kdump) like stack traces of
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# all the processes or a particular process and trapinfo.
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#
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# These macros can be used by copying this file in .gdbinit (put in home
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# directory or current directory) or by invoking gdb command with
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# --command=<command-file-name> option
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#
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# Credits:
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# Alexander Nyberg <alexn@telia.com>
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# V Srivatsa <vatsa@in.ibm.com>
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# Maneesh Soni <maneesh@in.ibm.com>
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#
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define bttnobp
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set $tasks_off=((size_t)&((struct task_struct *)0)->tasks)
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set $pid_off=((size_t)&((struct task_struct *)0)->pids[1].pid_list.next)
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set $init_t=&init_task
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set $next_t=(((char *)($init_t->tasks).next) - $tasks_off)
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while ($next_t != $init_t)
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set $next_t=(struct task_struct *)$next_t
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printf "\npid %d; comm %s:\n", $next_t.pid, $next_t.comm
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printf "===================\n"
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set var $stackp = $next_t.thread.esp
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set var $stack_top = ($stackp & ~4095) + 4096
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while ($stackp < $stack_top)
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if (*($stackp) > _stext && *($stackp) < _sinittext)
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info symbol *($stackp)
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end
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set $stackp += 4
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end
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set $next_th=(((char *)$next_t->pids[1].pid_list.next) - $pid_off)
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while ($next_th != $next_t)
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set $next_th=(struct task_struct *)$next_th
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printf "\npid %d; comm %s:\n", $next_t.pid, $next_t.comm
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printf "===================\n"
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set var $stackp = $next_t.thread.esp
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set var $stack_top = ($stackp & ~4095) + 4096
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while ($stackp < $stack_top)
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if (*($stackp) > _stext && *($stackp) < _sinittext)
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info symbol *($stackp)
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end
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set $stackp += 4
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end
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set $next_th=(((char *)$next_th->pids[1].pid_list.next) - $pid_off)
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end
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set $next_t=(char *)($next_t->tasks.next) - $tasks_off
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end
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end
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document bttnobp
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dump all thread stack traces on a kernel compiled with !CONFIG_FRAME_POINTER
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end
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define btt
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set $tasks_off=((size_t)&((struct task_struct *)0)->tasks)
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set $pid_off=((size_t)&((struct task_struct *)0)->pids[1].pid_list.next)
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set $init_t=&init_task
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set $next_t=(((char *)($init_t->tasks).next) - $tasks_off)
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while ($next_t != $init_t)
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set $next_t=(struct task_struct *)$next_t
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printf "\npid %d; comm %s:\n", $next_t.pid, $next_t.comm
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printf "===================\n"
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set var $stackp = $next_t.thread.esp
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set var $stack_top = ($stackp & ~4095) + 4096
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set var $stack_bot = ($stackp & ~4095)
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set $stackp = *($stackp)
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while (($stackp < $stack_top) && ($stackp > $stack_bot))
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set var $addr = *($stackp + 4)
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info symbol $addr
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set $stackp = *($stackp)
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end
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set $next_th=(((char *)$next_t->pids[1].pid_list.next) - $pid_off)
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while ($next_th != $next_t)
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set $next_th=(struct task_struct *)$next_th
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printf "\npid %d; comm %s:\n", $next_t.pid, $next_t.comm
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printf "===================\n"
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set var $stackp = $next_t.thread.esp
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set var $stack_top = ($stackp & ~4095) + 4096
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set var $stack_bot = ($stackp & ~4095)
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set $stackp = *($stackp)
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while (($stackp < $stack_top) && ($stackp > $stack_bot))
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set var $addr = *($stackp + 4)
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info symbol $addr
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set $stackp = *($stackp)
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end
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set $next_th=(((char *)$next_th->pids[1].pid_list.next) - $pid_off)
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end
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set $next_t=(char *)($next_t->tasks.next) - $tasks_off
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end
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end
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document btt
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dump all thread stack traces on a kernel compiled with CONFIG_FRAME_POINTER
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end
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define btpid
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set var $pid = $arg0
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set $tasks_off=((size_t)&((struct task_struct *)0)->tasks)
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set $pid_off=((size_t)&((struct task_struct *)0)->pids[1].pid_list.next)
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set $init_t=&init_task
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set $next_t=(((char *)($init_t->tasks).next) - $tasks_off)
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set var $pid_task = 0
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while ($next_t != $init_t)
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set $next_t=(struct task_struct *)$next_t
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if ($next_t.pid == $pid)
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set $pid_task = $next_t
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end
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set $next_th=(((char *)$next_t->pids[1].pid_list.next) - $pid_off)
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while ($next_th != $next_t)
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set $next_th=(struct task_struct *)$next_th
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if ($next_th.pid == $pid)
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set $pid_task = $next_th
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end
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set $next_th=(((char *)$next_th->pids[1].pid_list.next) - $pid_off)
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end
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set $next_t=(char *)($next_t->tasks.next) - $tasks_off
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end
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printf "\npid %d; comm %s:\n", $pid_task.pid, $pid_task.comm
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printf "===================\n"
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set var $stackp = $pid_task.thread.esp
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set var $stack_top = ($stackp & ~4095) + 4096
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set var $stack_bot = ($stackp & ~4095)
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set $stackp = *($stackp)
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while (($stackp < $stack_top) && ($stackp > $stack_bot))
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set var $addr = *($stackp + 4)
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info symbol $addr
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set $stackp = *($stackp)
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end
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end
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document btpid
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backtrace of pid
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end
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define trapinfo
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set var $pid = $arg0
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set $tasks_off=((size_t)&((struct task_struct *)0)->tasks)
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set $pid_off=((size_t)&((struct task_struct *)0)->pids[1].pid_list.next)
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set $init_t=&init_task
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set $next_t=(((char *)($init_t->tasks).next) - $tasks_off)
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set var $pid_task = 0
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while ($next_t != $init_t)
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set $next_t=(struct task_struct *)$next_t
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if ($next_t.pid == $pid)
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set $pid_task = $next_t
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end
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set $next_th=(((char *)$next_t->pids[1].pid_list.next) - $pid_off)
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while ($next_th != $next_t)
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set $next_th=(struct task_struct *)$next_th
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if ($next_th.pid == $pid)
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set $pid_task = $next_th
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end
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set $next_th=(((char *)$next_th->pids[1].pid_list.next) - $pid_off)
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end
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set $next_t=(char *)($next_t->tasks.next) - $tasks_off
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end
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printf "Trapno %ld, cr2 0x%lx, error_code %ld\n", $pid_task.thread.trap_no, \
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$pid_task.thread.cr2, $pid_task.thread.error_code
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end
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document trapinfo
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Run info threads and lookup pid of thread #1
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'trapinfo <pid>' will tell you by which trap & possibly
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address the kernel panicked.
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end
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define dmesg
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set $i = 0
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set $end_idx = (log_end - 1) & (log_buf_len - 1)
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while ($i < logged_chars)
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set $idx = (log_end - 1 - logged_chars + $i) & (log_buf_len - 1)
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if ($idx + 100 <= $end_idx) || \
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($end_idx <= $idx && $idx + 100 < log_buf_len)
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printf "%.100s", &log_buf[$idx]
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set $i = $i + 100
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else
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printf "%c", log_buf[$idx]
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set $i = $i + 1
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end
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end
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end
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document dmesg
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print the kernel ring buffer
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end
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477
Documentation/kdump/kdump.txt
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477
Documentation/kdump/kdump.txt
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================================================================
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Documentation for Kdump - The kexec-based Crash Dumping Solution
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================================================================
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This document includes overview, setup and installation, and analysis
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information.
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Overview
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========
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Kdump uses kexec to quickly boot to a dump-capture kernel whenever a
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dump of the system kernel's memory needs to be taken (for example, when
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the system panics). The system kernel's memory image is preserved across
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the reboot and is accessible to the dump-capture kernel.
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You can use common commands, such as cp and scp, to copy the
|
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memory image to a dump file on the local disk, or across the network to
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a remote system.
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Kdump and kexec are currently supported on the x86, x86_64, ppc64, ia64,
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and s390x architectures.
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When the system kernel boots, it reserves a small section of memory for
|
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the dump-capture kernel. This ensures that ongoing Direct Memory Access
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(DMA) from the system kernel does not corrupt the dump-capture kernel.
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The kexec -p command loads the dump-capture kernel into this reserved
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memory.
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|
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On x86 machines, the first 640 KB of physical memory is needed to boot,
|
||||
regardless of where the kernel loads. Therefore, kexec backs up this
|
||||
region just before rebooting into the dump-capture kernel.
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|
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Similarly on PPC64 machines first 32KB of physical memory is needed for
|
||||
booting regardless of where the kernel is loaded and to support 64K page
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size kexec backs up the first 64KB memory.
|
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|
||||
For s390x, when kdump is triggered, the crashkernel region is exchanged
|
||||
with the region [0, crashkernel region size] and then the kdump kernel
|
||||
runs in [0, crashkernel region size]. Therefore no relocatable kernel is
|
||||
needed for s390x.
|
||||
|
||||
All of the necessary information about the system kernel's core image is
|
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encoded in the ELF format, and stored in a reserved area of memory
|
||||
before a crash. The physical address of the start of the ELF header is
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||||
passed to the dump-capture kernel through the elfcorehdr= boot
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parameter. Optionally the size of the ELF header can also be passed
|
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when using the elfcorehdr=[size[KMG]@]offset[KMG] syntax.
|
||||
|
||||
|
||||
With the dump-capture kernel, you can access the memory image, or "old
|
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memory," in two ways:
|
||||
|
||||
- Through a /dev/oldmem device interface. A capture utility can read the
|
||||
device file and write out the memory in raw format. This is a raw dump
|
||||
of memory. Analysis and capture tools must be intelligent enough to
|
||||
determine where to look for the right information.
|
||||
|
||||
- Through /proc/vmcore. This exports the dump as an ELF-format file that
|
||||
you can write out using file copy commands such as cp or scp. Further,
|
||||
you can use analysis tools such as the GNU Debugger (GDB) and the Crash
|
||||
tool to debug the dump file. This method ensures that the dump pages are
|
||||
correctly ordered.
|
||||
|
||||
|
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Setup and Installation
|
||||
======================
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||||
|
||||
Install kexec-tools
|
||||
-------------------
|
||||
|
||||
1) Login as the root user.
|
||||
|
||||
2) Download the kexec-tools user-space package from the following URL:
|
||||
|
||||
http://kernel.org/pub/linux/utils/kernel/kexec/kexec-tools.tar.gz
|
||||
|
||||
This is a symlink to the latest version.
|
||||
|
||||
The latest kexec-tools git tree is available at:
|
||||
|
||||
git://git.kernel.org/pub/scm/utils/kernel/kexec/kexec-tools.git
|
||||
and
|
||||
http://www.kernel.org/pub/scm/utils/kernel/kexec/kexec-tools.git
|
||||
|
||||
There is also a gitweb interface available at
|
||||
http://www.kernel.org/git/?p=utils/kernel/kexec/kexec-tools.git
|
||||
|
||||
More information about kexec-tools can be found at
|
||||
http://horms.net/projects/kexec/
|
||||
|
||||
3) Unpack the tarball with the tar command, as follows:
|
||||
|
||||
tar xvpzf kexec-tools.tar.gz
|
||||
|
||||
4) Change to the kexec-tools directory, as follows:
|
||||
|
||||
cd kexec-tools-VERSION
|
||||
|
||||
5) Configure the package, as follows:
|
||||
|
||||
./configure
|
||||
|
||||
6) Compile the package, as follows:
|
||||
|
||||
make
|
||||
|
||||
7) Install the package, as follows:
|
||||
|
||||
make install
|
||||
|
||||
|
||||
Build the system and dump-capture kernels
|
||||
-----------------------------------------
|
||||
There are two possible methods of using Kdump.
|
||||
|
||||
1) Build a separate custom dump-capture kernel for capturing the
|
||||
kernel core dump.
|
||||
|
||||
2) Or use the system kernel binary itself as dump-capture kernel and there is
|
||||
no need to build a separate dump-capture kernel. This is possible
|
||||
only with the architectures which support a relocatable kernel. As
|
||||
of today, i386, x86_64, ppc64 and ia64 architectures support relocatable
|
||||
kernel.
|
||||
|
||||
Building a relocatable kernel is advantageous from the point of view that
|
||||
one does not have to build a second kernel for capturing the dump. But
|
||||
at the same time one might want to build a custom dump capture kernel
|
||||
suitable to his needs.
|
||||
|
||||
Following are the configuration setting required for system and
|
||||
dump-capture kernels for enabling kdump support.
|
||||
|
||||
System kernel config options
|
||||
----------------------------
|
||||
|
||||
1) Enable "kexec system call" in "Processor type and features."
|
||||
|
||||
CONFIG_KEXEC=y
|
||||
|
||||
2) Enable "sysfs file system support" in "Filesystem" -> "Pseudo
|
||||
filesystems." This is usually enabled by default.
|
||||
|
||||
CONFIG_SYSFS=y
|
||||
|
||||
Note that "sysfs file system support" might not appear in the "Pseudo
|
||||
filesystems" menu if "Configure standard kernel features (for small
|
||||
systems)" is not enabled in "General Setup." In this case, check the
|
||||
.config file itself to ensure that sysfs is turned on, as follows:
|
||||
|
||||
grep 'CONFIG_SYSFS' .config
|
||||
|
||||
3) Enable "Compile the kernel with debug info" in "Kernel hacking."
|
||||
|
||||
CONFIG_DEBUG_INFO=Y
|
||||
|
||||
This causes the kernel to be built with debug symbols. The dump
|
||||
analysis tools require a vmlinux with debug symbols in order to read
|
||||
and analyze a dump file.
|
||||
|
||||
Dump-capture kernel config options (Arch Independent)
|
||||
-----------------------------------------------------
|
||||
|
||||
1) Enable "kernel crash dumps" support under "Processor type and
|
||||
features":
|
||||
|
||||
CONFIG_CRASH_DUMP=y
|
||||
|
||||
2) Enable "/proc/vmcore support" under "Filesystems" -> "Pseudo filesystems".
|
||||
|
||||
CONFIG_PROC_VMCORE=y
|
||||
(CONFIG_PROC_VMCORE is set by default when CONFIG_CRASH_DUMP is selected.)
|
||||
|
||||
Dump-capture kernel config options (Arch Dependent, i386 and x86_64)
|
||||
--------------------------------------------------------------------
|
||||
|
||||
1) On i386, enable high memory support under "Processor type and
|
||||
features":
|
||||
|
||||
CONFIG_HIGHMEM64G=y
|
||||
or
|
||||
CONFIG_HIGHMEM4G
|
||||
|
||||
2) On i386 and x86_64, disable symmetric multi-processing support
|
||||
under "Processor type and features":
|
||||
|
||||
CONFIG_SMP=n
|
||||
|
||||
(If CONFIG_SMP=y, then specify maxcpus=1 on the kernel command line
|
||||
when loading the dump-capture kernel, see section "Load the Dump-capture
|
||||
Kernel".)
|
||||
|
||||
3) If one wants to build and use a relocatable kernel,
|
||||
Enable "Build a relocatable kernel" support under "Processor type and
|
||||
features"
|
||||
|
||||
CONFIG_RELOCATABLE=y
|
||||
|
||||
4) Use a suitable value for "Physical address where the kernel is
|
||||
loaded" (under "Processor type and features"). This only appears when
|
||||
"kernel crash dumps" is enabled. A suitable value depends upon
|
||||
whether kernel is relocatable or not.
|
||||
|
||||
If you are using a relocatable kernel use CONFIG_PHYSICAL_START=0x100000
|
||||
This will compile the kernel for physical address 1MB, but given the fact
|
||||
kernel is relocatable, it can be run from any physical address hence
|
||||
kexec boot loader will load it in memory region reserved for dump-capture
|
||||
kernel.
|
||||
|
||||
Otherwise it should be the start of memory region reserved for
|
||||
second kernel using boot parameter "crashkernel=Y@X". Here X is
|
||||
start of memory region reserved for dump-capture kernel.
|
||||
Generally X is 16MB (0x1000000). So you can set
|
||||
CONFIG_PHYSICAL_START=0x1000000
|
||||
|
||||
5) Make and install the kernel and its modules. DO NOT add this kernel
|
||||
to the boot loader configuration files.
|
||||
|
||||
Dump-capture kernel config options (Arch Dependent, ppc64)
|
||||
----------------------------------------------------------
|
||||
|
||||
1) Enable "Build a kdump crash kernel" support under "Kernel" options:
|
||||
|
||||
CONFIG_CRASH_DUMP=y
|
||||
|
||||
2) Enable "Build a relocatable kernel" support
|
||||
|
||||
CONFIG_RELOCATABLE=y
|
||||
|
||||
Make and install the kernel and its modules.
|
||||
|
||||
Dump-capture kernel config options (Arch Dependent, ia64)
|
||||
----------------------------------------------------------
|
||||
|
||||
- No specific options are required to create a dump-capture kernel
|
||||
for ia64, other than those specified in the arch independent section
|
||||
above. This means that it is possible to use the system kernel
|
||||
as a dump-capture kernel if desired.
|
||||
|
||||
The crashkernel region can be automatically placed by the system
|
||||
kernel at run time. This is done by specifying the base address as 0,
|
||||
or omitting it all together.
|
||||
|
||||
crashkernel=256M@0
|
||||
or
|
||||
crashkernel=256M
|
||||
|
||||
If the start address is specified, note that the start address of the
|
||||
kernel will be aligned to 64Mb, so if the start address is not then
|
||||
any space below the alignment point will be wasted.
|
||||
|
||||
|
||||
Extended crashkernel syntax
|
||||
===========================
|
||||
|
||||
While the "crashkernel=size[@offset]" syntax is sufficient for most
|
||||
configurations, sometimes it's handy to have the reserved memory dependent
|
||||
on the value of System RAM -- that's mostly for distributors that pre-setup
|
||||
the kernel command line to avoid a unbootable system after some memory has
|
||||
been removed from the machine.
|
||||
|
||||
The syntax is:
|
||||
|
||||
crashkernel=<range1>:<size1>[,<range2>:<size2>,...][@offset]
|
||||
range=start-[end]
|
||||
|
||||
'start' is inclusive and 'end' is exclusive.
|
||||
|
||||
For example:
|
||||
|
||||
crashkernel=512M-2G:64M,2G-:128M
|
||||
|
||||
This would mean:
|
||||
|
||||
1) if the RAM is smaller than 512M, then don't reserve anything
|
||||
(this is the "rescue" case)
|
||||
2) if the RAM size is between 512M and 2G (exclusive), then reserve 64M
|
||||
3) if the RAM size is larger than 2G, then reserve 128M
|
||||
|
||||
|
||||
|
||||
Boot into System Kernel
|
||||
=======================
|
||||
|
||||
1) Update the boot loader (such as grub, yaboot, or lilo) configuration
|
||||
files as necessary.
|
||||
|
||||
2) Boot the system kernel with the boot parameter "crashkernel=Y@X",
|
||||
where Y specifies how much memory to reserve for the dump-capture kernel
|
||||
and X specifies the beginning of this reserved memory. For example,
|
||||
"crashkernel=64M@16M" tells the system kernel to reserve 64 MB of memory
|
||||
starting at physical address 0x01000000 (16MB) for the dump-capture kernel.
|
||||
|
||||
On x86 and x86_64, use "crashkernel=64M@16M".
|
||||
|
||||
On ppc64, use "crashkernel=128M@32M".
|
||||
|
||||
On ia64, 256M@256M is a generous value that typically works.
|
||||
The region may be automatically placed on ia64, see the
|
||||
dump-capture kernel config option notes above.
|
||||
If use sparse memory, the size should be rounded to GRANULE boundaries.
|
||||
|
||||
On s390x, typically use "crashkernel=xxM". The value of xx is dependent
|
||||
on the memory consumption of the kdump system. In general this is not
|
||||
dependent on the memory size of the production system.
|
||||
|
||||
Load the Dump-capture Kernel
|
||||
============================
|
||||
|
||||
After booting to the system kernel, dump-capture kernel needs to be
|
||||
loaded.
|
||||
|
||||
Based on the architecture and type of image (relocatable or not), one
|
||||
can choose to load the uncompressed vmlinux or compressed bzImage/vmlinuz
|
||||
of dump-capture kernel. Following is the summary.
|
||||
|
||||
For i386 and x86_64:
|
||||
- Use vmlinux if kernel is not relocatable.
|
||||
- Use bzImage/vmlinuz if kernel is relocatable.
|
||||
For ppc64:
|
||||
- Use vmlinux
|
||||
For ia64:
|
||||
- Use vmlinux or vmlinuz.gz
|
||||
For s390x:
|
||||
- Use image or bzImage
|
||||
|
||||
|
||||
If you are using a uncompressed vmlinux image then use following command
|
||||
to load dump-capture kernel.
|
||||
|
||||
kexec -p <dump-capture-kernel-vmlinux-image> \
|
||||
--initrd=<initrd-for-dump-capture-kernel> --args-linux \
|
||||
--append="root=<root-dev> <arch-specific-options>"
|
||||
|
||||
If you are using a compressed bzImage/vmlinuz, then use following command
|
||||
to load dump-capture kernel.
|
||||
|
||||
kexec -p <dump-capture-kernel-bzImage> \
|
||||
--initrd=<initrd-for-dump-capture-kernel> \
|
||||
--append="root=<root-dev> <arch-specific-options>"
|
||||
|
||||
Please note, that --args-linux does not need to be specified for ia64.
|
||||
It is planned to make this a no-op on that architecture, but for now
|
||||
it should be omitted
|
||||
|
||||
Following are the arch specific command line options to be used while
|
||||
loading dump-capture kernel.
|
||||
|
||||
For i386, x86_64 and ia64:
|
||||
"1 irqpoll maxcpus=1 reset_devices"
|
||||
|
||||
For ppc64:
|
||||
"1 maxcpus=1 noirqdistrib reset_devices"
|
||||
|
||||
For s390x:
|
||||
"1 maxcpus=1 cgroup_disable=memory"
|
||||
|
||||
Notes on loading the dump-capture kernel:
|
||||
|
||||
* By default, the ELF headers are stored in ELF64 format to support
|
||||
systems with more than 4GB memory. On i386, kexec automatically checks if
|
||||
the physical RAM size exceeds the 4 GB limit and if not, uses ELF32.
|
||||
So, on non-PAE systems, ELF32 is always used.
|
||||
|
||||
The --elf32-core-headers option can be used to force the generation of ELF32
|
||||
headers. This is necessary because GDB currently cannot open vmcore files
|
||||
with ELF64 headers on 32-bit systems.
|
||||
|
||||
* The "irqpoll" boot parameter reduces driver initialization failures
|
||||
due to shared interrupts in the dump-capture kernel.
|
||||
|
||||
* You must specify <root-dev> in the format corresponding to the root
|
||||
device name in the output of mount command.
|
||||
|
||||
* Boot parameter "1" boots the dump-capture kernel into single-user
|
||||
mode without networking. If you want networking, use "3".
|
||||
|
||||
* We generally don' have to bring up a SMP kernel just to capture the
|
||||
dump. Hence generally it is useful either to build a UP dump-capture
|
||||
kernel or specify maxcpus=1 option while loading dump-capture kernel.
|
||||
|
||||
* For s390x there are two kdump modes: If a ELF header is specified with
|
||||
the elfcorehdr= kernel parameter, it is used by the kdump kernel as it
|
||||
is done on all other architectures. If no elfcorehdr= kernel parameter is
|
||||
specified, the s390x kdump kernel dynamically creates the header. The
|
||||
second mode has the advantage that for CPU and memory hotplug, kdump has
|
||||
not to be reloaded with kexec_load().
|
||||
|
||||
* For s390x systems with many attached devices the "cio_ignore" kernel
|
||||
parameter should be used for the kdump kernel in order to prevent allocation
|
||||
of kernel memory for devices that are not relevant for kdump. The same
|
||||
applies to systems that use SCSI/FCP devices. In that case the
|
||||
"allow_lun_scan" zfcp module parameter should be set to zero before
|
||||
setting FCP devices online.
|
||||
|
||||
Kernel Panic
|
||||
============
|
||||
|
||||
After successfully loading the dump-capture kernel as previously
|
||||
described, the system will reboot into the dump-capture kernel if a
|
||||
system crash is triggered. Trigger points are located in panic(),
|
||||
die(), die_nmi() and in the sysrq handler (ALT-SysRq-c).
|
||||
|
||||
The following conditions will execute a crash trigger point:
|
||||
|
||||
If a hard lockup is detected and "NMI watchdog" is configured, the system
|
||||
will boot into the dump-capture kernel ( die_nmi() ).
|
||||
|
||||
If die() is called, and it happens to be a thread with pid 0 or 1, or die()
|
||||
is called inside interrupt context or die() is called and panic_on_oops is set,
|
||||
the system will boot into the dump-capture kernel.
|
||||
|
||||
On powerpc systems when a soft-reset is generated, die() is called by all cpus
|
||||
and the system will boot into the dump-capture kernel.
|
||||
|
||||
For testing purposes, you can trigger a crash by using "ALT-SysRq-c",
|
||||
"echo c > /proc/sysrq-trigger" or write a module to force the panic.
|
||||
|
||||
Write Out the Dump File
|
||||
=======================
|
||||
|
||||
After the dump-capture kernel is booted, write out the dump file with
|
||||
the following command:
|
||||
|
||||
cp /proc/vmcore <dump-file>
|
||||
|
||||
You can also access dumped memory as a /dev/oldmem device for a linear
|
||||
and raw view. To create the device, use the following command:
|
||||
|
||||
mknod /dev/oldmem c 1 12
|
||||
|
||||
Use the dd command with suitable options for count, bs, and skip to
|
||||
access specific portions of the dump.
|
||||
|
||||
To see the entire memory, use the following command:
|
||||
|
||||
dd if=/dev/oldmem of=oldmem.001
|
||||
|
||||
|
||||
Analysis
|
||||
========
|
||||
|
||||
Before analyzing the dump image, you should reboot into a stable kernel.
|
||||
|
||||
You can do limited analysis using GDB on the dump file copied out of
|
||||
/proc/vmcore. Use the debug vmlinux built with -g and run the following
|
||||
command:
|
||||
|
||||
gdb vmlinux <dump-file>
|
||||
|
||||
Stack trace for the task on processor 0, register display, and memory
|
||||
display work fine.
|
||||
|
||||
Note: GDB cannot analyze core files generated in ELF64 format for x86.
|
||||
On systems with a maximum of 4GB of memory, you can generate
|
||||
ELF32-format headers using the --elf32-core-headers kernel option on the
|
||||
dump kernel.
|
||||
|
||||
You can also use the Crash utility to analyze dump files in Kdump
|
||||
format. Crash is available on Dave Anderson's site at the following URL:
|
||||
|
||||
http://people.redhat.com/~anderson/
|
||||
|
||||
|
||||
To Do
|
||||
=====
|
||||
|
||||
1) Provide relocatable kernels for all architectures to help in maintaining
|
||||
multiple kernels for crash_dump, and the same kernel as the system kernel
|
||||
can be used to capture the dump.
|
||||
|
||||
|
||||
Contact
|
||||
=======
|
||||
|
||||
Vivek Goyal (vgoyal@redhat.com)
|
||||
Maneesh Soni (maneesh@in.ibm.com)
|
||||
|
||||
Loading…
Add table
Add a link
Reference in a new issue