Do these 3 things before closing this tab:
1Repair Windows errors before they cause bigger problems2Fix the driver behind crashes, sound loss and screen glitches3Clear out junk files and repair common Windows errorsLinux eBPF execution has three distinct pieces: the verifier checks a loaded program’s instruction paths and tracked state before it can run; the kernel then runs it through an interpreter or a supported JIT path; and BPF maps provide typed, kernel-managed storage that programs and userspace can share. The exact context, permitted calls, and execution path depend on the program type, architecture, and kernel configuration.
What happens between loading an eBPF program and running it?
At a high level, userspace prepares a program and submits it through the BPF interface. The kernel checks the program with the verifier. If it passes, execution can use the interpreter or a JIT compiler where supported and enabled. When the program needs shared or persistent state, it can access an appropriate map through permitted helper operations; userspace can also operate on map entries through the BPF syscall.
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| Part | What it does | What it does not do |
|---|---|---|
| Verifier | Reasons about instruction paths and tracked register and stack state to check safety. | It does not translate the program into native instructions. |
| Interpreter or JIT | Executes the verified program, either by interpreting it or, on supported configurations, by translating it to native machine instructions. | JIT compilation does not replace verification. |
| BPF maps | Provide typed, kernel-managed storage that programs and userspace can access through their respective interfaces. | A map is not simply a process-local variable, and map types do not all have the same semantics. |
This is a general execution model, not a guarantee that every program, kernel, or architecture follows identical implementation details. The Linux kernel BPF documentation index describes the kernel-side documentation as work in progress; check the documentation and behavior for the target kernel when version-specific details matter.
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What does the verifier check?
The verifier analyzes the eBPF instructions submitted to the kernel; it does not certify arbitrary source code simply because it looks safe. It follows relevant instruction paths while tracking register and stack state, then checks that operations on those states are permitted. The kernel verifier documentation describes this state-based approach.
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Register and stack state
Tracked register states can include uninitialized values, scalars, and typed pointers. The verifier checks that a program does not read an uninitialized stack location, misuse a pointer, access memory outside established bounds, or pass invalid arguments to a function call. A value that has not been shown to be initialized or safe to use cannot be treated as though it were valid.
Ranges, offsets, and branches
For scalars, the verifier tracks signed and unsigned ranges as well as known and unknown bits. A branch can refine those bounds: after a condition has been established on a particular path, the verifier may be able to reason more precisely about the value on that path. For pointers, it tracks bases and offsets so it can assess access bounds and alignment. Consequently, code that appears plausible in C may still fail verification if the instruction paths do not establish the safety the verifier needs to prove.
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Context and permitted calls depend on program type
A program’s type determines which context fields and helper or function calls are available. A verifier decision is therefore tied to the program’s use case, not just to the instructions in isolation. Do not assume that a field or helper available to one kind of eBPF program is available to another.
Nullable map lookups need a check
A map lookup can produce either a pointer to a map value or NULL. A program must establish that the result is non-NULL before dereferencing it. The verifier tracks that distinction across control-flow paths; a check on one path does not make an unchecked use on another path safe.
Does eBPF always run as native machine code?
No. The kernel documents both interpreter execution and JIT compilation. A JIT compiler translates eBPF instructions into native machine instructions; interpreter execution is a separate path, documented in connection with __bpf_prog_run(). Whether a particular program is JITed depends on architecture support and system configuration.
What JIT compilation changes
On a supported JIT path, the kernel translates the verified eBPF program for the target architecture. The kernel’s Classic BPF vs eBPF documentation illustrates how eBPF registers can map to hardware registers on x86-64 and shows an example of generated machine code. These examples explain one architecture’s mapping; they are not a promise that other architectures emit the same code or provide identical JIT support.
Verification and JIT are separate stages
Verification establishes that the loaded program’s operations meet the verifier’s safety rules. JIT compilation changes how an accepted program is executed by translating it to native instructions. Native-code generation does not make an otherwise unverified program safe, and interpreter execution does not mean verification can be skipped.
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The kernel documentation describes maps as generic storage for sharing data between kernel and userspace. A map is a kernel-managed object with a type and defined key/value or specialized semantics, rather than an ordinary variable belonging to one process. eBPF programs use permitted helper functions to access maps; userspace creates maps and looks up, updates, or deletes entries through the BPF syscall. See the kernel’s BPF maps documentation.
Choose a map by the operation and semantics
Map families include arrays, hashes, per-CPU variants, queues, stacks, LPM tries, and specialized networking or storage maps. They are not interchangeable: their access patterns and semantics differ. Choose according to the data operation the program needs rather than treating one map type as universally best.
Map access is shared, but lookup is not guaranteed to succeed
A program can use a permitted helper to look up an entry, but it must handle a nullable lookup result before using the value pointer. Userspace can operate on entries through the map’s BPF interface as well. This shared access is the point of the map abstraction; it does not remove the need to follow the map type’s rules or the program type’s permitted interfaces.
Map lifetime depends on references and setup
Userspace receives a file descriptor when it creates a map. The kernel documentation explains that maps held by open file descriptors are deleted automatically when a process exits; lifetime should not be generalized beyond the references and setup involved. In particular, account for whether references remain open and whether the map is pinned when reasoning about when a specific map is removed.
How the three pieces fit together
- Userspace submits a program. A loader or other userspace component prepares the program and sends it to the kernel through the BPF interface.
- The verifier reasons about its instructions. It checks control flow, tracked state, memory accesses, pointer use, and the rules for the relevant program type. For a map lookup, the program must establish a non-NULL result before dereferencing it.
- The kernel chooses an execution path. An accepted program can run through the interpreter or a supported JIT path, depending on architecture and configuration.
- The program accesses shared state when needed. It uses permitted helper operations for its map type; userspace can use the BPF syscall to operate on map entries.
Keep the handoffs distinct: the verifier checks safety, the interpreter or JIT executes the accepted instructions, and maps hold shared data. Those roles are related, but none substitutes for the others.
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