fix(memtrack): track successful posix_memalign allocations

[not-matthias]

Problem

posix_memalign was attached to the shared memalign uprobe handler (UPROBE_ARG_RET), which assumes the standard allocator ABI. But posix_memalign(void** memptr, size_t alignment, size_t size) is inverted:

• Returns int 0 on success (nonzero errno on failure), not a pointer.
• Delivers the allocated pointer through the memptr out-parameter, not the return register.
• Size lives in PARM3 (PARM2 is the alignment).

The shared handler gated success on a non-NULL return and used the return register as the address. Since successful posix_memalign returns 0, every successful allocation was treated as a failure and silently dropped.

Fix

Dedicated uprobe/uretprobe pair for posix_memalign:

• uprobe stashes memptr (PARM1) and size (PARM3) keyed by tid.
• uretprobe gates on RC == 0, reads the address back from *memptr via bpf_probe_read_user, then submits an aligned-alloc event.

Test

Added posix_memalign_test to the existing rstest table in tests/c_tests.rs with a fixture + snapshot confirming the allocation is now tracked.

[greptile-apps]

Greptile Summary

Adds dedicated posix_memalign allocation tracking and expands memtrack with per-process RSS lifecycle accounting.

• Captures successful posix_memalign allocations through its out-parameter while dropping failed calls.
• Adds RSS, reverse-map, fork, exec, and exit events with userspace parsing and state reconstruction.
• Introduces optional allocator tracking, kernel compatibility handling, and expanded x86_64/ARM integration coverage.
• Updates the shared memtrack artifact representation and adds allocation and RSS fixtures and snapshots.

Confidence Score: 5/5

The PR appears safe to merge because no eligible blocking failures remain.

No blocking failure remains.

Important Files Changed

Filename	Overview
crates/memtrack/src/ebpf/c/allocator.h	Adds dedicated entry and return probes that capture the posix_memalign out-parameter and size according to its ABI.
crates/memtrack/src/ebpf/memtrack/allocator.rs	Routes discovered posix_memalign symbols to the dedicated probe pair.
crates/memtrack/src/ebpf/c/rss.bpf.h	Adds RSS and reverse-map collection with process ownership and lifecycle tracking.
crates/memtrack/src/ebpf/events.rs	Parses the new RSS, reverse-map, fork, exec, and exit event variants.
crates/memtrack/src/ebpf/tracker.rs	Supports trackers with optional allocator probes and optional reverse-map hooks.
crates/runner-shared/src/artifacts/memtrack/mod.rs	Extends the shared memtrack event model for RSS and process lifecycle data.
crates/memtrack/tests/c_tests.rs	Adds successful and failing posix_memalign integration coverage.
crates/memtrack/tests/rss_tests.rs	Adds integration coverage for RSS reconstruction across mapping and process lifecycle scenarios.
.github/workflows/ci.yml	Runs memtrack test shards, including RSS tests, on x86_64 and ARM Ubuntu runners.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart LR
    A[Allocator and kernel probes] --> B[eBPF event ring buffer]
    B --> C[Rust event parser]
    C --> D[Memtrack artifact encoder]
    D --> E[Allocation and per-process RSS results]
    F[IPC enable or disable] --> A
    G[Fork, exec, and exit hooks] --> B

Loading

_{Reviews (2): Last reviewed commit: "test(memtrack): assert failing posix_mem..." | Re-trigger Greptile}

[codspeed-hq]

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.

✅ 17 untouched benchmarks

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_{Comparing cod-3238-memtrack-drops-all-successful-posix_memalign-allocations (b9aeda1) with cod-3231-support-disabling-allocator-tracking (131f8a3)}