bpf: skip compat hooks when !IA32_EMULATION

[kxxt]

Summary by CodeRabbit

• Bug Fixes

  • Improved compatibility syscall hook handling on x86_64 systems.
  • Prevented unsupported compatibility hooks from loading when the kernel lacks required configuration.
  • Added clearer handling for environments where kernel configuration cannot be read.

• Tests

  • Added coverage for enabled, disabled, and unavailable compatibility configuration scenarios.
  • Updated compatibility execution-event tests to skip when the required hooks are unavailable.

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Project	Deployment	Actions	Updated (UTC)
tracexec	Ready	Preview, Comment	Jul 18, 2026 2:49pm

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yml

Review profile: CHILL

Plan: Pro

Run ID: 32705941-0edb-4093-95f5-db893a89f3aa

📥 Commits

Reviewing files that changed from the base of the PR and between 939083b and 2836a0d.

📒 Files selected for processing (4)

• crates/tracexec-backend-ebpf/src/bin/verifier_complexity.rs
• crates/tracexec-backend-ebpf/src/probe.rs
• crates/tracexec-backend-ebpf/src/tracer.rs
• crates/tracexec-backend-ebpf/tests/exec_events.rs

---

Walkthrough

Changes

The PR adds x86_64 kernel-configuration detection for CONFIG_IA32_EMULATION and applies it to compat syscall hook autoloading, verifier cases, and execution-event tests.

Compat syscall hook gating

Layer / File(s)	Summary
Kernel configuration decision crates/tracexec-backend-ebpf/src/probe.rs	Adds and tests should_load_compat_syscall_hooks, including enabled, absent, and unavailable configuration cases.
Runtime and verifier gating crates/tracexec-backend-ebpf/src/tracer.rs, crates/tracexec-backend-ebpf/src/bin/verifier_complexity.rs	Disables compat program autoloading and skips compat fentry cases when CONFIG_IA32_EMULATION is unavailable.
Compat event test gating crates/tracexec-backend-ebpf/tests/exec_events.rs	Skips the compat execution-event test when compat hooks should not load.

Estimated code review effort: 3 (Moderate) | ~20 minutes

Sequence Diagram(s)

sequenceDiagram
  participant EbpfTracer
  participant KernelConfig
  participant CompatHooks
  participant ExecEventsTest
  EbpfTracer->>KernelConfig: check CONFIG_IA32_EMULATION
  KernelConfig-->>EbpfTracer: loading decision
  EbpfTracer->>CompatHooks: disable autoload when unavailable
  ExecEventsTest->>KernelConfig: check CONFIG_IA32_EMULATION
  KernelConfig-->>ExecEventsTest: test decision

Loading

Possibly related issues

• Skip loading compat eBPF syscall hooks when kernel does not support legacy 32bit programs #281 — Directly addresses detecting missing CONFIG_IA32_EMULATION and skipping compat hooks across loading, tracing, verification, and tests.

Possibly related PRs

• kxxt/tracexec#206 — Modifies the same x86_64 compat syscall handling components, including verifier and tracer behavior.
• kxxt/tracexec#268 — Modifies compat syscall execution-event tests with conditional skipping.

Suggested labels: full-ci

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly matches the main change: conditionally skipping compat BPF hooks when IA32_EMULATION is absent.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch ebpf-32bit

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[gemini-code-assist]

Code Review

This pull request introduces conditional loading of compat syscall hooks based on the kernel configuration (CONFIG_IA32_EMULATION) on x86_64 platforms, preventing load failures when legacy 32-bit emulation is disabled. Feedback on the changes suggests explicitly disabling these compat programs on all non-x86_64 architectures (such as aarch64 or riscv64) in both the tracer and the verifier complexity tool to avoid load failures on those platforms. Additionally, it is recommended to replace Option::is_none_or with map_or to maintain compatibility with older Rust toolchains.

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[gemini-code-assist]

Option::is_none_or was stabilized in Rust 1.82.0. To maintain compatibility with older Rust toolchains (MSRV), we can use map_or(true, ...) which is functionally identical and supported since Rust 1.0.0.

Suggested change

	kconfig.is_none_or(|configs| configs.contains_key("CONFIG_IA32_EMULATION"))
	kconfig.map_or(true, |configs| configs.contains_key("CONFIG_IA32_EMULATION"))

[codecov]

Codecov Report

❌ Patch coverage is 48.48485% with 17 lines in your changes missing coverage. Please review.
✅ Project coverage is 82.21%. Comparing base (939083b) to head (2836a0d).

Files with missing lines	Patch %	Lines
...acexec-backend-ebpf/src/bin/verifier_complexity.rs	0.00%	13 Missing ⚠️
crates/tracexec-backend-ebpf/src/tracer.rs	33.33%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #297      +/-   ##
==========================================
- Coverage   82.25%   82.21%   -0.05%     
==========================================
  Files          84       84              
  Lines       21026    21057      +31     
==========================================
+ Hits        17295    17311      +16     
- Misses       3731     3746      +15     

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