Aaron Merey

Aaron Merey

Aaron Merey is a Software Engineer at Red Hat where he is a member of the Platform Tools team.

Recent Posts

Introducing debuginfod, the elfutils debuginfo server

Introducing debuginfod, the elfutils debuginfo server

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By Aaron Merey

Because bugs are inevitable, developers need quick and easy access to the artifacts that debugging tools like Systemtap and GDB depend on, which are typically DWARF (Debugging With Attributed Record Formats) debuginfo or source files. Accessing these resources should not be an issue when debugging your own local build tree, but all too often they are not readily available.

For example, your distro might package debuginfo and source files separately from the executable you’re trying to debug and you may lack the permissions to install these packages. Or, perhaps you’re debugging within a container that was not built with these resources, or maybe you simply don’t want these files taking up space on your machine.

Debuginfo files are notorious for taking up large amounts of space, and it is not unusual for their size to be five to fifteen times that of the corresponding executable. debuginfod aims to resolve these problems.

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SystemTap’s BPF Backend Introduces Tracepoint Support

SystemTap’s BPF Backend Introduces Tracepoint Support

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By Aaron Merey

This blog is the third in a series on stapbpf, SystemTap’s BPF (Berkeley Packet Filter) backend. In the first post, Introducing stapbpf – SystemTap’s new BPF backend, I explain what BPF is and what features it brings to SystemTap. In the second post, What are BPF Maps and how are they used in stapbpf, I examine BPF maps, one of BPF’s key components, and their role in stapbpf’s implementation.

In this post, I introduce stapbpf’s recently added support for tracepoint probes. Tracepoints are statically-inserted hooks in the Linux kernel onto which user-defined probes can be attached. Tracepoints can be found in a variety of locations throughout the Linux kernel, including performance-critical subsystems such as the scheduler. Therefore, tracepoint probes must terminate quickly in order to avoid significant performance penalties or unusual behavior in these subsystems. BPF’s lack of loops and limit of 4k instructions means that it’s sufficient for this task.

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What are BPF Maps and how are they used in stapbpf

What are BPF Maps and how are they used in stapbpf

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By Aaron Merey

Compared to SystemTap’s default backend, one of stapbpf’s most distinguishing features is the absence of a kernel module runtime. The BPF machinery inside the kernel instead mostly handles its runtime. Therefore it would be very helpful if BPF provided us with a way for states to be maintained across multiple invocations of BPF programs and for userspace programs to be able to communicate with BPF programs. This is accomplished by BPF maps. In this blog post, I will introduce BPF maps and explain their role in stapbpf’s implementation.

What are BPF maps?

BPF maps are essentially generic data structures consisting of key/value pairs. They are created from userspace using the BPF system call, which returns a file descriptor for the map. The key size and value size are specified by the user, allowing for the storage of key/value pairs with arbitrary types. Once a map is created, elements can be accessed from userspace using the BPF system call. Maps are automatically deallocated once the user process that created the map terminates (although it is possible to force the map to persist longer than this process). Stapbpf uses the following function to create new BPF maps.

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Introducing stapbpf – SystemTap’s new BPF backend

Introducing stapbpf – SystemTap’s new BPF backend

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By Aaron Merey

SystemTap 3.2 includes an early prototype of SystemTap’s new BPF backend (stapbpf). It represents a first step towards leveraging powerful new tracing and performance analysis capabilities recently added to the Linux kernel. In this post, I will compare the translation process of stapbpf with the default backend (stap) and compare some differences in functionality between these two backends.

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