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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 sys-
     tem 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 ini-
     tialized 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	re-
     turned.

     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 at-
     tempted, 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	ex-
     tended by Robert Watson for general-purpose use outside of	ddb(4).

FreeBSD	13.0		       January 31, 2020			  FreeBSD 13.0

NAME | SYNOPSIS | DESCRIPTION | RETURN VALUES | SEE ALSO | AUTHORS

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