Manual Pages  — STACK

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.