SYNOPSISIn sys/param.h In sys/stack.h In the kernel configuration file: options DDB options STACK Ft struct stack * Fn stack_create void Ft void Fn stack_destroy struct stack *st Ft int Fn stack_put struct stack *st vm_offset_t pc Ft void Fn stack_copy const struct stack *src struct stack dst Ft void Fn stack_zero struct stack *st Ft void Fn stack_print const struct stack *st Ft void Fn stack_print_ddb const struct stack *st Ft void Fn stack_print_short const struct stack *st Ft void Fn stack_print_short_ddb const struct stack *st Ft void Fn stack_sbuf_print struct sbuf sb* const struct stack *st Ft void Fn stack_sbuf_print_ddb struct sbuf sb* const struct stack *st Ft void Fn stack_save struct stack *st
DESCRIPTIONThe 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 Vt struct stack . Before a trace may be created or otherwise manipulated, storage for the trace must be allocated with Fn stack_create , which may sleep. Memory associated with a trace is freed by calling Fn stack_destroy .
A trace of the current kernel thread's call stack may be captured using Fn stack_save .
Fn stack_print and Fn 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 Fn stack_print_ddb and Fn 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.
Fn 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 Fn 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.