[PATCH v8 0/5] Tracepoints and static branch in Rust

Alice Ryhl
2024-08-22T12:04:50Z

An important part of a production ready Linux kernel driver is
tracepoints. So to write production ready Linux kernel drivers in Rust,
we must be able to call tracepoints from Rust code. This patch series
adds support for calling tracepoints declared in C from Rust.

This series includes a patch that adds a user of tracepoits to the
rust_print sample. Please see that sample for details on what is needed
to use this feature in Rust code.

This is intended for use in the Rust Binder driver, which was originally
sent as an RFC [1]. The RFC did not include tracepoint support, but you
can see how it will be used in Rust Binder at [2]. The author has
verified that the tracepoint support works on Android devices.

This implementation implements support for static keys in Rust so that
the actual static branch happens in the Rust object file. However, the
__DO_TRACE body remains in C code. See v1 for an implementation where
__DO_TRACE is also implemented in Rust.

When compiling for x86, this patchset has a dependency on [3] as we need
objtool to convert jmp instructions to nop instructions. This patchset
is based on top of the series containing [3].

There is also a conflict with splitting up the C helpers [4]. I've
included an alternate version of the first patch that shows how to
resolve the conflict. When using the alternate version of the first
patch, this series applies cleanly on top of rust-next.

Both [3] and [4] are already in rust-next.

Link: https://lore.kernel.org/rust-for-linux/20231101-rust-binder-v1-0-08ba9197f637@google.com/ [1]
Link: https://r.android.com/3119993 [2]
Link: https://lore.kernel.org/all/20240725183325.122827-7-ojeda@kernel.org/ [3]
Link: https://lore.kernel.org/all/20240815103016.2771842-1-nmi@metaspace.dk/ [4]
Signed-off-by: Alice Ryhl <aliceryhl@google.com>
---
Changes in v8:
- Use OBJTREE instead of SRCTREE for temporary asm file.
- Adjust comments on `asm!` wrapper to be less confusing.
- Include resolution of conflict with helpers splitting.
- Link to v7: https://lore.kernel.org/r/20240816-tracepoint-v7-0-d609b916b819@google.com

Changes in v7:
- Fix spurious file included in first patch.
- Fix issue with riscv asm.
- Fix tags on fourth patch to match fifth patch.
- Add Reviewed-by/Acked-by tags where appropriate.
- Link to v6: https://lore.kernel.org/r/20240808-tracepoint-v6-0-a23f800f1189@google.com

Changes in v6:
- Add support for !CONFIG_JUMP_LABEL.
- Add tracepoint to rust_print sample.
- Deduplicate inline asm.
- Require unsafe inside `declare_trace!`.
- Fix bug on x86 due to use of intel syntax.
- Link to v5: https://lore.kernel.org/r/20240802-tracepoint-v5-0-faa164494dcb@google.com

Changes in v5:
- Update first patch regarding inline asm duplication.
- Add __rust_do_trace helper to support conditions.
- Rename DEFINE_RUST_DO_TRACE_REAL to __DEFINE_RUST_DO_TRACE.
- Get rid of glob-import in tracepoint macro.
- Address safety requirements on tracepoints in docs.
- Link to v4: https://lore.kernel.org/rust-for-linux/20240628-tracepoint-v4-0-353d523a9c15@google.com

Changes in v4:
- Move arch-specific code into rust/kernel/arch.
- Restore DEFINE_RUST_DO_TRACE at end of define_trace.h
- Link to v3: https://lore.kernel.org/r/20240621-tracepoint-v3-0-9e44eeea2b85@google.com

Changes in v3:
- Support for Rust static_key on loongarch64 and riscv64.
- Avoid failing compilation on architectures that are missing Rust
static_key support when the archtectures does not actually use it.
- Link to v2: https://lore.kernel.org/r/20240610-tracepoint-v2-0-faebad81b355@google.com

Changes in v2:
- Call into C code for __DO_TRACE.
- Drop static_call patch, as it is no longer needed.
- Link to v1: https://lore.kernel.org/r/20240606-tracepoint-v1-0-6551627bf51b@google.com

---
Alice Ryhl (5):
rust: add generic static_key_false
rust: add tracepoint support
rust: samples: add tracepoint to Rust sample
jump_label: adjust inline asm to be consistent
rust: add arch_static_branch

MAINTAINERS | 1 +
arch/arm/include/asm/jump_label.h | 14 +++--
arch/arm64/include/asm/jump_label.h | 20 +++++---
arch/loongarch/include/asm/jump_label.h | 16 +++---
arch/riscv/include/asm/jump_label.h | 50 ++++++++++--------
arch/x86/include/asm/jump_label.h | 38 ++++++--------
include/linux/tracepoint.h | 22 +++++++-
include/trace/define_trace.h | 12 +++++
include/trace/events/rust_sample.h | 31 +++++++++++
rust/Makefile | 5 +-
rust/bindings/bindings_helper.h | 3 ++
rust/helpers.c | 9 ++++
rust/kernel/.gitignore | 3 ++
rust/kernel/arch_static_branch_asm.rs.S | 7 +++
rust/kernel/jump_label.rs | 91 +++++++++++++++++++++++++++++++++
rust/kernel/lib.rs | 37 ++++++++++++++
rust/kernel/tracepoint.rs | 49 ++++++++++++++++++
samples/rust/Makefile | 3 +-
samples/rust/rust_print.rs | 18 +++++++
samples/rust/rust_print_events.c | 8 +++
scripts/Makefile.build | 9 +++-
21 files changed, 379 insertions(+), 67 deletions(-)
---
base-commit: 88359b25b950670432ef1da4352eb6cc62e0fa9f
change-id: 20240606-tracepoint-31e15b90e471

Best regards,
--
Alice Ryhl <aliceryhl@google.com>