[RFC PATCH v2 0/3] tools: Add Rust library build infrastructure and prefer zlib-rs

[Ian Rogers]

The zlib-rs project (https://github.com/trifectatechfoundation/zlib-rs)
provides a memory-safe, high-performance Rust implementation of the zlib
compression specification along with a C ABI layer (libz-rs-sys) that is a
drop-in replacement for the standard C zlib library. Transitioning
decompression of kernel configuration files (/proc/config.gz), compressed
ELF/BTF sections, and perf data from C zlib to zlib-rs improves both memory
safety and decompression performance.

On many Linux distributions (such as Debian, Ubuntu, and Fedora), Rust
crates like zlib-rs and libz-rs-sys are packaged as Cargo registry sources
under /usr/share/cargo/registry/ (e.g. librust-libz-rs-sys-dev or
rust-libz-rs-sys-devel) rather than as prebuilt C shared libraries, while
other environments may install prebuilt libz_rs libraries via pkg-config or
a custom prefix (LIBZ_RS_DIR).

This RFC series lays the groundwork for building and linking Rust crate
libraries in tools/ offline from the system Cargo registry and integrates
zlib-rs support into perf and bpftool, preferring zlib-rs over C zlib when
available:

1. **tools build: Add Rust library build infrastructure and zlib-rs feature test**:
   - Adds `tools/build/Makefile.rust` with helpers to resolve C compiler and
     linker flags for Rust libraries via `%-cflags` and `%-libs` targets.
   - Resolves `zlib-rs` compiler and linker flags via `LIBZ_RS_DIR`,
     `pkg-config` (`libz-rs-sys-cdylib`, `zlib-rs`, `z_rs`), or building
     `libz_rs.a` (with the `export-symbols`, `c-allocator`, `std`, and `gz`
     features) into `$(OUTPUT)libz_rs/` from `/usr/share/cargo/registry`
     using offline Cargo (`cargo metadata --offline` and
     `cargo build --offline`).
   - Adds `tools/build/feature/test-zlib-rs.c` checking
     `ZLIB_VER_SUBREVISION == 15` (`0xf`, which distinguishes
     `libz-rs-sys`'s `zlib.h` from standard C `zlib.h`) and linking against
     `inflateInit()`.
   - Extends `tools/scripts/Makefile.include` with cross-compilation target
     triples (`RUST_TARGET_FLAGS_<arch>`) and the `feature_rust_lib` macro.

2. **perf build: Prefer zlib-rs over zlib when available**:
   - Moves Rust detection ahead of zlib detection in
     `tools/perf/Makefile.config` and prefers `zlib-rs` over C `zlib` unless
     `NO_ZLIB_RS=1` (or `NO_ZLIB=1` / `NO_RUST=1`) is set.
   - Defines both `HAVE_ZLIB_SUPPORT` and `HAVE_ZLIB_RS_SUPPORT` when
     `zlib-rs` is used so existing zlib call sites in `perf` work unchanged
     while `perf version --build-options` and `perf check feature zlib-rs`
     report whether `zlib-rs` is active.
   - Shares `$(OUTPUT)libz_rs/` with the host bootstrap `bpftool` build in
     `tools/perf/bpf_skel.mak` and adds `NO_ZLIB` / `NO_ZLIB_RS` tests to
     `tools/perf/tests/make`.

3. **bpftool: Prefer zlib-rs over zlib when available**:
   - Adds `zlib-rs` and `zlib` to `FEATURE_TESTS` and `FEATURE_DISPLAY` in
     `tools/bpf/bpftool/Makefile` and configures `ZLIB_CFLAGS` and
     `ZLIB_LIBS` via `feature_rust_lib` when `zlib-rs` is detected.

Changes in v2:
- Use offline Cargo (`cargo metadata --offline` and `cargo build --offline`
  configured against `CARGO_REGISTRY_DIR` = `/usr/share/cargo/registry` and
  isolated from `~/.cargo`) to resolve crate versions, dependency graphs,
  features, and build scripts instead of manually globbing crate directory
  names and invoking `rustc` on hardcoded `.rlib` edges (Miguel Ojeda).
- Avoid including `../../scripts/Makefile.arch` in `tools/bpf/bpftool/Makefile`
  (to keep the standalone bpftool mirror self-contained) by placing
  `RUST_TARGET_FLAGS_<arch>` in `tools/scripts/Makefile.include`, and expand
  the bpftool commit message on the security and performance motivation for
  preferring `zlib-rs` (Quentin Monnet).
- Drop unused `.rlib` pattern rules and helpers from `tools/build/Build.include`
  and `tools/build/Makefile.build` (Sashiko).
- Address Sashiko review feedback on `PKG_CONFIG` handling when unset or with
  `-static`, `test-all.bin` re-checking `zlib-rs` and `rust`, preserving
  `EXTRA_CFLAGS` optimization defaults when building `libbpf.a`, and
  honoring `NO_ZLIB_RS=1` in `bpftool` when `FEATURES_DUMP` is used.

AI Assistance Disclosure (per Documentation/process/coding-assistants.rst
and Documentation/process/generated-content.rst):
- Tools used: Antigravity coding assistant and Sashiko automated patch
  review using Gemini 4 LLMs.
- Summary of prompts and assistance: Interactive pair-programming session to
  identify distro packaging for zlib-rs/libz-rs-sys, implement the zlib-rs
  feature test and offline Cargo build rules in Makefile.rust, integrate
  zlib-rs detection into perf and bpftool, separate Rust library outputs
  into $(OUTPUT)libz_rs/, and address reviewer and automated Sashiko
  feedback.
- Testing performed: Built and tested perf and bpftool with zlib-rs
  (default), NO_ZLIB_RS=1 (fallback to C zlib), NO_ZLIB=1, and MINIMAL=1;
  verified `perf version --build-options`, `perf check feature`, and the
  `make_no_zlib` / `make_no_zlib_rs` tests in `tools/perf/tests/make`; and
  checked all commits with `scripts/checkpatch.pl`.

Ian Rogers (3):
  tools build: Add Rust library build infrastructure and zlib-rs feature
    test
  perf build: Prefer zlib-rs over zlib when available
  bpftool: Prefer zlib-rs over zlib when available

 tools/bpf/bpftool/.gitignore             |   1 +
 tools/bpf/bpftool/Makefile               |  57 +++++++++-
 tools/build/Makefile.feature             |  12 +-
 tools/build/Makefile.rust                | 160 +++++++++++++++++++++++
 tools/build/feature/.gitignore           |   1 +
 tools/build/feature/Makefile             |  11 +-
 tools/build/feature/test-zlib-rs.c       |  19 +++
 tools/perf/.gitignore                    |   1 +
 tools/perf/Documentation/perf-check.txt  |   1 +
 tools/perf/Makefile.config               |  88 +++++++------
 tools/perf/Makefile.perf                 |  32 ++++-
 tools/perf/bpf_skel.mak                  |   8 +-
 tools/perf/builtin-check.c               |   1 +
 tools/perf/scripts/install-build-deps.sh |   6 +
 tools/perf/tests/make                    |   9 ++
 tools/scripts/Makefile.include           |  25 ++++
 16 files changed, 382 insertions(+), 50 deletions(-)
 create mode 100644 tools/build/Makefile.rust
 create mode 100644 tools/build/feature/test-zlib-rs.c

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