STACK(9)               FreeBSD 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(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);

     int
     stack_save_td(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 thread's kernel call stack may be captured using
     stack_save().  stack_save_td() can be used to capture the kernel stack of
     a caller-specified thread.  Callers of these functions must own the
     thread lock of the specified thread, and the thread's stack must not be
     swapped out.  stack_save_td() can capture the kernel stack of a running
     thread, though note that this is not implemented on all platforms.  If
     the thread is running, the caller must also hold the process lock for the
     target 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() returns 0 when the stack capture was successful and a
     non-zero error number otherwise.  In particular, EBUSY 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).

FreeBSD 13.1-RELEASE-p6        January 31, 2020        FreeBSD 13.1-RELEASE-p6