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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. It can be declared in
stack_save(). stack_save_td() can be used to capture the kernel stack of
a caller-specified thread. Callers of stack_save_td() 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 14.0-RELEASE-p6 March 6, 2022 FreeBSD 14.0-RELEASE-p6