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PSTACK(1)		FreeBSD	General	Commands Manual		     PSTACK(1)

     pstack -- print the backtrace of the running program

     pstack [-loOtv] [-a arg count] [-f	frame count] pid

     The pstack	utility	prints the stack backtraces for	the running program.
     The pstack	attaches to the	traced process using the ptrace(2) debugging
     interface.	 If possible, the symbolic name	and offset for the function
     executing in each frame is	displayed.  The	pstack can be directed to
     print the shared object name, which contains the function.

     The first line of the output displays the pid of the traced process, bi-
     nary name as reported by the kernel, and the currently active osrel ver-
     sion of the ABI for the process.  After that, for each thread in the
     process, the thread id is displayed, followed by the backtrace.

     The following options are available:

     -a	count
	     Try to guess the arguments	of each	function appearing in the
	     backtrace.	 Not more than count arguments are printed for each
	     function.	Ability	to correctly read the argument values depends
	     on	the architecture and compiler optimization, but	it is gener-
	     ally impossible to	do.

     -f	count
	     For each thread, print not	more than count	frames in the back-

     -l	     Instead of	walking	the stacks of the running threads, print the
	     names of the shared objects loaded	into the process address
	     space.  The output	of the utility resembles the output of ldd(1)
	     command run on the	binary.

     -o	     Show the names of the objects which contain the location of the
	     frame current instruction pointer.

     -O	     Same as -o, but displays the full path to the objects instead of
	     only names.

     -t	     Measure and print the time	which the target process was suspended
	     to	walk the stack frames.

     -v	     Be	verbose.

     gdb(1), ldd(1), ptrace(2),	libunwind(3), procfs(5)

     The pstack	command	is reimplemented by Konstantin Belousov	to mimic the
     user interface of other similar pstack utilities, in particular, the
     pstack written by
     Peter Edwards.  This version relies on the	libunwind library as the stack
     unwinding backend.

     On	i386, the argument printing code assumes that the frame	layout is
     standard, which is	currently often	not the	case due to the	padding	added
     between return address and	previous frame pointer,	as done	by compilers
     to	align the stack.

     On	amd64, the argument printing currently does not	work.  The amd64 ABI
     specifies that integer arguments are passed in the	registers which	are
     not required to be	preserved across function calls.  As the result, there
     is	typically no way to re-create the arguments values on any frame	except
     the current one.

     The symbol	names cannot be	inferred if the	corresponding binary or	shared
     object are	already	deleted, since libunwind needs to read the symbols
     from the on-disk ELF image.  This could typically occur if	the binary or
     library is	reinstalled, but the process uses older	version	of the binary
     with the same name.

     The pstack	only works on the processes executing ELF binaries.

     You cannot	get a backtrace	for the	process, to which another debugger is
     currently attached.  The ptrace(2)	debugging mechanism used to obtain the
     neccessary	live process information causes	some syscalls to return	EINTR
     errors on pstack detach.

     The pstack	utility	cannot yet extract a backtrace from the	core dump.

     The architecture of the program and pstack	shall match (this is libunwind

FreeBSD	13.0			 June 17, 2014			  FreeBSD 13.0


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