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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_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
     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(), 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() 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() variant 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.


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).