feat(memtrack): support running the memory instrument in the macro-agent sandbox by GuillaumeLagrange · Pull Request #443 · CodSpeedHQ/codspeed

GuillaumeLagrange · 2026-07-08T02:15:57Z

Make the memory instrument work when the runner and codspeed-memtrack run inside the macro-agent sandbox — unprivileged, in a user + PID namespace, with a delegated BPF token instead of root/file-capabilities. Companion to the platform PR that sets up the token and the exe-gate.

Three things had to change:

Attach via bpf()-native links. memtrack attached uprobes through perf_event_open and a perf tracepoint, which a BPF token cannot authorize (they are gated on CAP_PERFMON in the init user namespace). Switch the allocation probes to uprobe_multi links and sched_process_fork to tp_btf, both of which attach through the bpf() syscall a token covers. The eBPF logic is unchanged. Symbols are resolved to file offsets ourselves and attached by offset, since libbpf's uprobe_multi symbol resolution returned ENOENT for libc allocator symbols (which silently captured zero events).
Resolve PIDs relative to the tracker's PID namespace. Inside a PID namespace the PIDs memtrack registers are namespace-local while eBPF sees global PIDs, so nothing matched. Read PIDs relative to memtrack's own PID namespace (bpf_get_ns_current_pid_tgid for the current task, a CO-RE walk of task->thread_pid->numbers[level] for the fork tracepoint). In the init namespace this resolves to global PIDs, preserving existing behavior.
Accept a delegated BPF token as a privilege source. The memory executor required root or memtrack file-capabilities and otherwise bailed (and prompted for sudo). Treat a live LIBBPF_BPF_TOKEN_PATH as satisfied privilege, and make grant_privileges a no-op when a token is present.

The token half is transparent to memtrack — libbpf picks the token up from LIBBPF_BPF_TOKEN_PATH; no explicit token code.

Proven end-to-end on the macro-runner with the platform side: codspeed run -m memory on an instrumented divan bench runs inside the sandbox and uploads to staging (run 6a4dae30d60d9ec8e172062b, peak 28.5 KB / 140 allocations).

Refs COD-3047

greptile-apps · 2026-07-08T02:18:13Z

Greptile Summary

This PR makes memory tracking work in the macro-agent sandbox. The main changes are:

Adds token and perf eBPF skeleton variants.
Uses bpf-native links for token-based attachment.
Resolves tracked PIDs relative to memtrack's PID namespace.
Treats delegated BPF tokens as a privilege source.
Adds flavor-equivalence coverage for the two attach paths.

Confidence Score: 4/5

This is close, but the realloc tracking gap should be fixed before merging.

Realloc entry probes still compare the host PID against namespace-local tracked PIDs.
In the sandbox, that can drop realloc events without an error.
The rest of the token and namespace wiring is narrowly scoped.

crates/memtrack/src/ebpf/c/memtrack.bpf.c

Important Files Changed

Filename	Overview
crates/memtrack/src/ebpf/c/memtrack.bpf.c	Adds attach-mode selection and namespace-aware PID helpers, but the realloc-family entry path still checks the host PID.
crates/memtrack/src/ebpf/memtrack.rs	Adds token/perf skeleton selection, offset-based uprobe attachment, and PID namespace rodata setup.
src/executor/memory/executor.rs	Accepts delegated BPF tokens as an alternative to root or memtrack file capabilities.

Comments Outside Diff (1)

crates/memtrack/src/ebpf/c/memtrack.bpf.c, line 319-321 (link)

Realloc uses host PID

In the sandbox, userspace registers the namespace-local PID in tracked_pids, but this entry probe still checks tid >> 32, which is the host PID. When those values differ, this branch returns before saving realloc_args, and the return probe has no arguments to emit the realloc event. Realloc allocations are then silently missing from the memory trace.

Prompt To Fix With AI

This is a comment left during a code review.
Path: crates/memtrack/src/ebpf/c/memtrack.bpf.c
Line: 319-321

Comment:
**Realloc uses host PID**

In the sandbox, userspace registers the namespace-local PID in `tracked_pids`, but this entry probe still checks `tid >> 32`, which is the host PID. When those values differ, this branch returns before saving `realloc_args`, and the return probe has no arguments to emit the realloc event. Realloc allocations are then silently missing from the memory trace.

How can I resolve this? If you propose a fix, please make it concise.

Prompt To Fix All With AI

Fix the following 1 code review issue. Work through them one at a time, proposing concise fixes.

---

### Issue 1 of 1
crates/memtrack/src/ebpf/c/memtrack.bpf.c:319-321
**Realloc uses host PID**

In the sandbox, userspace registers the namespace-local PID in `tracked_pids`, but this entry probe still checks `tid >> 32`, which is the host PID. When those values differ, this branch returns before saving `realloc_args`, and the return probe has no arguments to emit the realloc event. Realloc allocations are then silently missing from the memory trace.

_{Reviews (4): Last reviewed commit: "feat(memtrack): allow memtrack usage wit..." | Re-trigger Greptile}

codspeed-hq · 2026-07-08T02:19:52Z

Merging this PR will not alter performance

⚠️

Unknown Walltime execution environment detected

Using the Walltime instrument on standard Hosted Runners will lead to inconsistent data.

For the most accurate results, we recommend using CodSpeed Macro Runners: bare-metal machines fine-tuned for performance measurement consistency.

✅ 7 untouched benchmarks

_{Comparing cod-3047-support-memory-instrument-on-macro-agent-sandbox (81c4b15) with main (3278ec8)}

greptile-apps Bot reviewed Jul 8, 2026

View reviewed changes

Comment thread crates/memtrack/src/ebpf/c/memtrack.bpf.c

Comment thread crates/memtrack/src/ebpf/memtrack.rs

Comment thread src/executor/memory/executor.rs

GuillaumeLagrange force-pushed the cod-3047-support-memory-instrument-on-macro-agent-sandbox branch 2 times, most recently from b3e73df to b2f8ac7 Compare July 8, 2026 13:48

greptile-apps Bot reviewed Jul 8, 2026

View reviewed changes

Comment thread crates/memtrack/src/ebpf/memtrack.rs

Comment thread src/executor/memory/executor.rs

GuillaumeLagrange force-pushed the cod-3047-support-memory-instrument-on-macro-agent-sandbox branch from b2f8ac7 to 94d981a Compare July 8, 2026 14:06

feat(memtrack): allow memtrack usage with a bpf token

81c4b15

GuillaumeLagrange force-pushed the cod-3047-support-memory-instrument-on-macro-agent-sandbox branch from 94d981a to 81c4b15 Compare July 8, 2026 14:15

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feat(memtrack): support running the memory instrument in the macro-agent sandbox#443

feat(memtrack): support running the memory instrument in the macro-agent sandbox#443
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GuillaumeLagrange commented Jul 8, 2026

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Greptile Summary

Confidence Score: 4/5

Important Files Changed

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codspeed-hq Bot commented Jul 8, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

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Merging this PR will not alter performance

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greptile-apps Bot commented Jul 8, 2026 •

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