registerkprobe

register_kprobe is a Linux kernel API function used to activate a kprobe, a dynamic instrumentation mechanism that allows probing of kernel code at runtime. A kprobe is described by a struct kprobe, which identifies the target point either by an exact instruction address (kp.addr) or by a kernel symbol name (kp.symbol_name). In addition to the target, the struct can specify optional callbacks such as a pre_handler (executed before the target instruction), a post_handler (executed after), and a fault_handler (invoked if a fault occurs while handling the probe). After configuring the struct, a caller—typically a kernel module—invokes register_kprobe(&kp) to install the probe. If registration succeeds, the kernel places a breakpoint at the target and the handlers are invoked on hits. The function returns 0 on success or a negative errno on failure (for example, -EINVAL for invalid parameters, -ENOENT if the specified symbol cannot be found, -EBUSY if a probe already exists at the target).

Probes remain active until they are removed with unregister_kprobe(&kp) or until the module is unloaded. unregister_kprobe cleans up resources and restores the original code at the target.

Use cases for register_kprobe include debugging, runtime tracing, and lightweight performance measurements without recompiling the kernel. It is part of the kprobe framework, which also includes kretprobe for return-path probes and uprobes for user-space probes. Important considerations include potential performance impact, safety constraints about where probes can be placed, and the need for lightweight handlers to avoid undue overhead. Developers are advised to consult current kernel documentation for detailed constraints and best practices, as behavior can vary across kernel versions.