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STACK(9)		    Kernel Developer's Manual			STACK(9)

NAME
     stack -- kernel thread stack tracing routines

SYNOPSIS
     #include <sys/param.h>
     #include <sys/stack.h>
     In the kernel configuration file:
     options DDB
     options STACK

     struct stack *
     stack_create(void);

     void
     stack_destroy(struct stack *st);

     int
     stack_put(struct stack *st, vm_offset_t pc);

     void
     stack_copy(struct stack *src, struct stack dst);

     void
     stack_zero(struct stack *st);

     void
     stack_print(struct stack *st);

     void
     stack_print_ddb(struct stack *st);

     void
     stack_print_short(struct stack *st);

     void
     stack_print_short_ddb(struct stack *st);

     void
     stack_sbuf_print(struct sbuf sb*, struct stack *st);

     void
     stack_sbuf_print_ddb(struct sbuf sb*, struct stack *st);

     void
     stack_save(struct stack *st);

DESCRIPTION
     The stack KPI allows querying of kernel stack trace information and the au-
     tomated generation of kernel stack trace strings for the purposes of debug-
     ging  and tracing.  To use the KPI, at least one of options DDB and options
     STACK must be compiled into the kernel.

     Each stack trace is described by a struct stack.  Before  a  trace  may  be
     created  or  otherwise manipulated, storage for the trace must be allocated
     with stack_create(), which may sleep.  Memory associated with  a  trace  is
     freed by calling stack_destroy().

     A	trace  of  the	current kernel thread's call stack may be captured using
     stack_save().

     stack_print() and stack_print_short() may be used to print  a  stack  trace
     using  the  kernel  printf(9), and may sleep as a result of acquiring sx(9)
     locks in the kernel linker while looking up symbol names.	In  locking-sen-
     sitive    environments,	the    unsynchronized	 stack_print_ddb()   and
     stack_print_short_ddb() variants may be invoked.	This  function	bypasses
     kernel linker locking, making it usable in ddb(4), but not in a live system
     where linker data structures may change.

     stack_sbuf_print()  may  be  used to construct a human-readable string, in-
     cluding conversion  (where  possible)  from  a  simple  kernel  instruction
     pointer  to a named symbol and offset.  The argument sb must be an initial-
     ized struct sbuf as described in sbuf(9).	This function may  sleep  if  an
     auto-extending  struct  sbuf  is used, or due to kernel linker locking.  In
     locking-sensitive	environments,  such  as   ddb(4),   the   unsynchronized
     stack_sbuf_print_ddb()  variant may be invoked to avoid kernel linker lock-
     ing; it should be used with a fixed-length sbuf.

     The utility functions stack_zero, stack_copy, and stack_put may be used  to
     manipulate stack data structures directly.

SEE ALSO
     ddb(4), printf(9), sbuf(9), sx(9)

AUTHORS
     The  stack(9)  function  suite was created by Antoine Brodin.  stack(9) was
     extended by Robert Watson for general-purpose use outside of ddb(4).

FreeBSD 8.2			  June 24, 2009 			STACK(9)
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