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(int flags);

       void
       stack_destroy(struct stack *st);

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

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

       void
       stack_zero(struct stack *st);

       void
       stack_print(const struct stack *st);

       void
       stack_print_ddb(const struct stack *st);

       void
       stack_print_short(const struct stack *st);

       void
       stack_print_short_ddb(const struct stack *st);

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

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

       void
       stack_save(struct stack *st);

       void
       stack_save_td(struct stack *st, struct thread *td);

       int
       stack_save_td_running(struct stack *st, struct thread *td);

DESCRIPTION

       The  stack  KPI  allows querying of kernel stack trace information and the automated generation of kernel
       stack trace strings for the purposes of debugging 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().  The flags argument is passed to malloc(9).
       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_save_td()
       and  stack_save_td_running() can also be used to capture the stack of a caller-specified thread.  Callers
       of these functions must own the thread lock of the specified thread.   stack_save_td()  can  capture  the
       stack   of   a   kernel   thread  that  is  not  running  or  swapped  out  at  the  time  of  the  call.
       stack_save_td_running() can capture the stack of a running kernel thread.

       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-sensitive 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,  including conversion (where
       possible) from a simple kernel instruction pointer to a named symbol and offset.  The argument sb must be
       an initialized 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 locking; 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.

RETURN VALUES

       stack_put() returns 0 on success.  Otherwise the struct stack does not contain space to record additional
       frames, and a non-zero value is returned.

       stack_save_td_running()  returns  0  when  the  stack  capture was successful and a non-zero error number
       otherwise.  In particular, EAGAIN is returned if the thread was running in user mode at the time that the
       capture was attempted, and EOPNOTSUPP is returned if the operation is not implemented.

SEE ALSO

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

AUTHORS

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

Debian                                           October 6, 2017                                        STACK(9)