uprobes

uprobes are a dynamic tracing and debugging facility in the Linux kernel. They allow a user-space program to dynamically insert probes into the kernel's execution path without requiring any modifications to the kernel source code. This capability is invaluable for understanding kernel behavior, diagnosing performance issues, and debugging complex systems.

The concept of probes in general refers to points in a program's execution where instrumentation can be inserted. Traditionally, these probes were often static, meaning they had to be compiled into the code. uprobes, however, are dynamic, meaning they can be attached and detached at runtime. This makes them particularly useful for live systems where recompiling the kernel is not feasible or desirable.

uprobes work by redirecting a specific instruction at a user-defined address. When the program execution reaches that address, it is diverted to a handler provided by the user-space tracing tool. This handler can then perform various actions, such as logging the event, inspecting register values, or collecting performance metrics, before allowing execution to resume from the original instruction.

The primary use cases for uprobes include performance analysis, where they can pinpoint bottlenecks in kernel code, and security auditing, where they can track sensitive system calls or memory accesses. Debugging kernel modules or drivers is another common application, enabling developers to observe the internal workings of the kernel without intrusive debugging symbols.

SystemTap and bpftrace are popular tools that leverage uprobes (and other tracing mechanisms like kprobes) to provide powerful scripting capabilities for dynamic kernel analysis. These tools allow users to write simple scripts that specify which kernel functions or code locations to probe and what actions to take when a probe is hit.