[PATCH v2 00/13] Support several Rust toolchain versions

[PATCH v2 00/13] Support several Rust toolchain versions

[Miguel Ojeda]

Hi all,

A few things improved here and there, and rebased on top of `rust-next`.

The changelog is attached to each patch.

I kept the `Tested-by`s since most of the changes are on documentation
or comments, though I did remove them on the patch that changed the most
just in case (even for that one, I think Benno's and Andreas' setup
would not have made a difference).

I plan to put this series into `rust-next` very soon so that it goes
into the merge window.

Previous cover letter:

  v1: https://lore.kernel.org/rust-for-linux/20240701183625.665574-1-ojeda@kernel.org/

Thanks!

Cheers,
Miguel

Miguel Ojeda (13):
  rust: macros: indent list item in `paste!`'s docs
  rust: init: simplify from `map_err` to `inspect_err`
  rust: allow `dead_code` for never constructed bindings
  rust: relax most deny-level lints to warnings
  rust: simplify Clippy warning flags set
  rust: start supporting several compiler versions
  rust: avoid assuming a particular `bindgen` build
  rust: work around `bindgen` 0.69.0 issue
  rust: start supporting several `bindgen` versions
  rust: warn about `bindgen` versions 0.66.0 and 0.66.1
  kbuild: rust: add `rustc-version` support
  rust: support the new `-Zub-checks` flag
  docs: rust: quick-start: add section on Linux distributions

 Documentation/process/changes.rst        |   9 +-
 Documentation/rust/quick-start.rst       | 136 +++++++++++++++++------
 Makefile                                 |  31 +++---
 init/Kconfig                             |  11 +-
 lib/Kconfig.debug                        |  18 +++
 rust/Makefile                            |   4 +-
 rust/bindings/lib.rs                     |   1 +
 rust/kernel/init.rs                      |  13 +--
 rust/macros/lib.rs                       |   2 +-
 rust/uapi/lib.rs                         |   1 +
 scripts/Kconfig.include                  |   6 +
 scripts/Makefile.compiler                |   4 +
 scripts/rust_is_available.sh             |  33 +++---
 scripts/rust_is_available_bindgen_0_66.h |   2 +
 scripts/rust_is_available_test.py        |  59 ++++++----
 scripts/rustc-version.sh                 |  52 +++++++++
 16 files changed, 274 insertions(+), 108 deletions(-)
 create mode 100644 scripts/rust_is_available_bindgen_0_66.h
 create mode 100755 scripts/rustc-version.sh


base-commit: fc6e66f4696b63b8a2645a2bcea407cb04bd0666
--
2.45.2

[PATCH v2 04/13] rust: relax most deny-level lints to warnings

[Miguel Ojeda]

Since we are starting to support several Rust toolchains, lints (including
Clippy ones) now may behave differently and lint groups may include
new lints.

Therefore, to maximize the chances a given version works, relax some
deny-level lints to warnings. It may also make our lives a bit easier
while developing new code or refactoring.

To be clear, the requirements for in-tree code are still the same, since
Rust code still needs to be warning-free (patches should be clean under
`WERROR=y`) and the set of lints is not changed.

`unsafe_op_in_unsafe_fn` is left unmodified, i.e. as an error, since it is
becoming the default in the language (warn-by-default in Rust 2024 [1] and
ideally an error later on) and thus it should also be very well tested. In
addition, it is simple enough that it should not have false positives
(unlike e.g. `rust_2018_idioms`'s `explicit_outlives_requirements`).

`non_ascii_idents` is left unmodified as well, i.e. as an error, since
it is unlikely one gains any productivity during development if it
were a warning (in fact, it may be worse, since it is likely one made
a typo). In addition, it should not have false positives.

Finally, put the two `-D` ones at the top and take the chance to do one
per line.

Link: https://github.com/rust-lang/rust/pull/112038 [1]
Reviewed-by: Finn Behrens <me@kloenk.dev>
Tested-by: Benno Lossin <benno.lossin@proton.me>
Tested-by: Andreas Hindborg <a.hindborg@samsung.com>
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
---
v2:
  - Kept `non_ascii_idents` as an error. (Björn, Finn)

 Makefile      | 24 +++++++++++++-----------
 rust/Makefile |  4 ++--
 2 files changed, 15 insertions(+), 13 deletions(-)

diff --git a/Makefile b/Makefile
index fea263aaa492..7ea526814fdb 100644
--- a/Makefile
+++ b/Makefile
@@ -461,17 +461,19 @@ KBUILD_USERLDFLAGS := $(USERLDFLAGS)
 # host programs.
 export rust_common_flags := --edition=2021 \
 			    -Zbinary_dep_depinfo=y \
-			    -Dunsafe_op_in_unsafe_fn -Drust_2018_idioms \
-			    -Dunreachable_pub -Dnon_ascii_idents \
+			    -Dunsafe_op_in_unsafe_fn \
+			    -Dnon_ascii_idents \
+			    -Wrust_2018_idioms \
+			    -Wunreachable_pub \
 			    -Wmissing_docs \
-			    -Drustdoc::missing_crate_level_docs \
-			    -Dclippy::correctness -Dclippy::style \
-			    -Dclippy::suspicious -Dclippy::complexity \
-			    -Dclippy::perf \
-			    -Dclippy::let_unit_value -Dclippy::mut_mut \
-			    -Dclippy::needless_bitwise_bool \
-			    -Dclippy::needless_continue \
-			    -Dclippy::no_mangle_with_rust_abi \
+			    -Wrustdoc::missing_crate_level_docs \
+			    -Wclippy::correctness -Wclippy::style \
+			    -Wclippy::suspicious -Wclippy::complexity \
+			    -Wclippy::perf \
+			    -Wclippy::let_unit_value -Wclippy::mut_mut \
+			    -Wclippy::needless_bitwise_bool \
+			    -Wclippy::needless_continue \
+			    -Wclippy::no_mangle_with_rust_abi \
 			    -Wclippy::dbg_macro

 KBUILD_HOSTCFLAGS   := $(KBUILD_USERHOSTCFLAGS) $(HOST_LFS_CFLAGS) $(HOSTCFLAGS)
@@ -572,7 +574,7 @@ KBUILD_RUSTFLAGS := $(rust_common_flags) \
 		    -Csymbol-mangling-version=v0 \
 		    -Crelocation-model=static \
 		    -Zfunction-sections=n \
-		    -Dclippy::float_arithmetic
+		    -Wclippy::float_arithmetic

 KBUILD_AFLAGS_KERNEL :=
 KBUILD_CFLAGS_KERNEL :=
diff --git a/rust/Makefile b/rust/Makefile
index 385378311322..bf05e65365da 100644
--- a/rust/Makefile
+++ b/rust/Makefile
@@ -367,7 +367,7 @@ ifneq ($(or $(CONFIG_ARM64),$(and $(CONFIG_RISCV),$(CONFIG_64BIT))),)
 endif

 $(obj)/core.o: private skip_clippy = 1
-$(obj)/core.o: private skip_flags = -Dunreachable_pub
+$(obj)/core.o: private skip_flags = -Wunreachable_pub
 $(obj)/core.o: private rustc_objcopy = $(foreach sym,$(redirect-intrinsics),--redefine-sym $(sym)=__rust$(sym))
 $(obj)/core.o: private rustc_target_flags = $(core-cfgs)
 $(obj)/core.o: $(RUST_LIB_SRC)/core/src/lib.rs FORCE
@@ -381,7 +381,7 @@ $(obj)/compiler_builtins.o: $(src)/compiler_builtins.rs $(obj)/core.o FORCE
 	+$(call if_changed_dep,rustc_library)

 $(obj)/alloc.o: private skip_clippy = 1
-$(obj)/alloc.o: private skip_flags = -Dunreachable_pub
+$(obj)/alloc.o: private skip_flags = -Wunreachable_pub
 $(obj)/alloc.o: private rustc_target_flags = $(alloc-cfgs)
 $(obj)/alloc.o: $(RUST_LIB_SRC)/alloc/src/lib.rs $(obj)/compiler_builtins.o FORCE
 	+$(call if_changed_dep,rustc_library)
--
2.45.2

[PATCH v2 05/13] rust: simplify Clippy warning flags set

[Miguel Ojeda]

All Clippy lint groups that we enable, except `correctness`, have a
default `warn` level, thus they may be removed now that we relaxed all
lints to `warn`.

Moreover, Clippy provides an `all` lint group that covers the groups
we enable by default. Thus just use `all` instead -- the only change is
that, if Clippy introduces a new lint group or splits an existing one,
we will cover that one automatically.

In addition, `let_unit_value` is in `style` since Rust 1.62.0, thus it
does not need to be enabled manually.

Reviewed-by: Finn Behrens <me@kloenk.dev>
Tested-by: Benno Lossin <benno.lossin@proton.me>
Tested-by: Andreas Hindborg <a.hindborg@samsung.com>
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
---
 Makefile | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/Makefile b/Makefile
index 7ea526814fdb..9044fdb9adb1 100644
--- a/Makefile
+++ b/Makefile
@@ -467,10 +467,8 @@ export rust_common_flags := --edition=2021 \
 			    -Wunreachable_pub \
 			    -Wmissing_docs \
 			    -Wrustdoc::missing_crate_level_docs \
-			    -Wclippy::correctness -Wclippy::style \
-			    -Wclippy::suspicious -Wclippy::complexity \
-			    -Wclippy::perf \
-			    -Wclippy::let_unit_value -Wclippy::mut_mut \
+			    -Wclippy::all \
+			    -Wclippy::mut_mut \
 			    -Wclippy::needless_bitwise_bool \
 			    -Wclippy::needless_continue \
 			    -Wclippy::no_mangle_with_rust_abi \
-- 
2.45.2

[PATCH v2 11/13] kbuild: rust: add `rustc-version` support

[Miguel Ojeda]

Now that we are starting to support several Rust versions, introduce
`rustc-version` support, mimicking the C side:

  - `scripts/rustc-version.sh`, that mimics the other version scripts
     (with one more digit, e.g. Rust 1.79.0 is 107900).

  - `rustc-{info,name,version}` Kbuild macros.

  - `CONFIG_RUSTC_VERSION` Kconfig symbol that calls `rustc-version`.

  - `rustc-min-version` Kbuild macro that uses `CONFIG_RUSTC_VERSION`.

With these, we can easily support flags conditionally depending on
`rustc`'s version -- a user comes in the next patch.

Another user will be the `-Ctarget-feature=+reserve-x18`/`-Zfixed-x18`
arm64 flags [1].

Link: https://lore.kernel.org/rust-for-linux/20240305-shadow-call-stack-v2-1-c7b4a3f4d616@google.com/ [1]
Reviewed-by: Finn Behrens <me@kloenk.dev>
Tested-by: Benno Lossin <benno.lossin@proton.me>
Tested-by: Andreas Hindborg <a.hindborg@samsung.com>
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
---
v2:
  - Fix comment from "5 or 6-digit" to "6 to 7-digit".

 init/Kconfig              |  6 +++++
 scripts/Kconfig.include   |  6 +++++
 scripts/Makefile.compiler |  4 +++
 scripts/rustc-version.sh  | 52 +++++++++++++++++++++++++++++++++++++++
 4 files changed, 68 insertions(+)
 create mode 100755 scripts/rustc-version.sh

diff --git a/init/Kconfig b/init/Kconfig
index 94e20d3b99d4..7d344f248785 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -1920,6 +1920,12 @@ config RUST

 	  If unsure, say N.

+config RUSTC_VERSION
+	int
+	depends on RUST
+	default $(rustc-version)
+	default 0
+
 config RUSTC_VERSION_TEXT
 	string
 	depends on RUST
diff --git a/scripts/Kconfig.include b/scripts/Kconfig.include
index 3ee8ecfb8c04..82ab889725db 100644
--- a/scripts/Kconfig.include
+++ b/scripts/Kconfig.include
@@ -45,6 +45,12 @@ $(error-if,$(success,test -z "$(cc-info)"),Sorry$(comma) this C compiler is not
 cc-name := $(shell,set -- $(cc-info) && echo $1)
 cc-version := $(shell,set -- $(cc-info) && echo $2)

+# Get the Rust compiler name, version, and error out if it is not supported.
+rustc-info := $(shell,$(srctree)/scripts/rustc-version.sh $(RUSTC))
+$(error-if,$(success,test -z "$(rustc-info)"),Sorry$(comma) this Rust compiler is not supported.)
+rustc-name := $(shell,set -- $(rustc-info) && echo $1)
+rustc-version := $(shell,set -- $(rustc-info) && echo $2)
+
 # Get the assembler name, version, and error out if it is not supported.
 as-info := $(shell,$(srctree)/scripts/as-version.sh $(CC) $(CLANG_FLAGS))
 $(error-if,$(success,test -z "$(as-info)"),Sorry$(comma) this assembler is not supported.)
diff --git a/scripts/Makefile.compiler b/scripts/Makefile.compiler
index 92be0c9a13ee..17eaa085b59c 100644
--- a/scripts/Makefile.compiler
+++ b/scripts/Makefile.compiler
@@ -69,6 +69,10 @@ gcc-min-version = $(call test-ge, $(CONFIG_GCC_VERSION), $1)
 # Usage: cflags-$(call clang-min-version, 110000) += -foo
 clang-min-version = $(call test-ge, $(CONFIG_CLANG_VERSION), $1)

+# rustc-min-version
+# Usage: rustflags-$(call rustc-min-version, 107900) += -foo
+rustc-min-version = $(call test-ge, $(CONFIG_RUSTC_VERSION), $1)
+
 # ld-option
 # Usage: KBUILD_LDFLAGS += $(call ld-option, -X, -Y)
 ld-option = $(call try-run, $(LD) $(KBUILD_LDFLAGS) $(1) -v,$(1),$(2),$(3))
diff --git a/scripts/rustc-version.sh b/scripts/rustc-version.sh
new file mode 100755
index 000000000000..7b27ab5d4ecd
--- /dev/null
+++ b/scripts/rustc-version.sh
@@ -0,0 +1,52 @@
+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0
+#
+# Print the Rust compiler name and its version in a 6 or 7-digit form.
+# Also, perform the minimum version check.
+
+set -e
+
+# Convert the version string x.y.z to a canonical up-to-7-digits form.
+#
+# Note that this function uses one more digit (compared to other
+# instances in other version scripts) to give a bit more space to
+# `rustc` since it will reach 1.100.0 in late 2026.
+get_canonical_version()
+{
+	IFS=.
+	set -- $1
+	echo $((100000 * $1 + 100 * $2 + $3))
+}
+
+orig_args="$@"
+
+set -- $("$@" --version)
+
+name=$1
+
+min_tool_version=$(dirname $0)/min-tool-version.sh
+
+case "$name" in
+rustc)
+	version=$2
+	min_version=$($min_tool_version rustc)
+	;;
+*)
+	echo "$orig_args: unknown Rust compiler" >&2
+	exit 1
+	;;
+esac
+
+rustcversion=$(get_canonical_version $version)
+min_rustcversion=$(get_canonical_version $min_version)
+
+if [ "$rustcversion" -lt "$min_rustcversion" ]; then
+	echo >&2 "***"
+	echo >&2 "*** Rust compiler is too old."
+	echo >&2 "***   Your $name version:    $version"
+	echo >&2 "***   Minimum $name version: $min_version"
+	echo >&2 "***"
+	exit 1
+fi
+
+echo $name $rustcversion
--
2.45.2

[PATCH v2 12/13] rust: support the new `-Zub-checks` flag

[Miguel Ojeda]

Rust 1.79.0 has introduced a new codegen flag, `-Zub-checks` [1], to
allow to independently configure (from `-Cdebug-assertions`) whether the
extra runtime checks for UB are emitted, in a similar fashion to
`-Coverflow-checks`.

This allows to configure the kernel with only the UB checks enabled,
but not the `debug_assert!`s; or vice versa, e.g. [2].

It also showcases how `RUSTC_VERSION` and the Kbuild macros, introduced
in the previous commit, can be used.

Link: https://github.com/rust-lang/compiler-team/issues/725 [1]
Link: https://godbolt.org/z/jY69ezx5K [2]
Reviewed-by: Finn Behrens <me@kloenk.dev>
Tested-by: Benno Lossin <benno.lossin@proton.me>
Tested-by: Andreas Hindborg <a.hindborg@samsung.com>
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
---
 Makefile          |  9 +++++++--
 lib/Kconfig.debug | 18 ++++++++++++++++++
 2 files changed, 25 insertions(+), 2 deletions(-)

diff --git a/Makefile b/Makefile
index 9044fdb9adb1..4cf3b9799ec9 100644
--- a/Makefile
+++ b/Makefile
@@ -821,10 +821,15 @@ KBUILD_CFLAGS += -Os
 KBUILD_RUSTFLAGS += -Copt-level=s
 endif
 
-# Always set `debug-assertions` and `overflow-checks` because their default
-# depends on `opt-level` and `debug-assertions`, respectively.
+# Always set `debug-assertions` because its default depends on `opt-level`.
 KBUILD_RUSTFLAGS += -Cdebug-assertions=$(if $(CONFIG_RUST_DEBUG_ASSERTIONS),y,n)
+
+# Always set `overflow-checks` and `ub-checks` because their default depends on
+# `debug-assertions`.
 KBUILD_RUSTFLAGS += -Coverflow-checks=$(if $(CONFIG_RUST_OVERFLOW_CHECKS),y,n)
+ifeq ($(call rustc-min-version, 107900),y)
+KBUILD_RUSTFLAGS += -Zub-checks=$(if $(CONFIG_RUST_UNDEFINED_BEHAVIOR_CHECKS),y,n)
+endif
 
 # Tell gcc to never replace conditional load with a non-conditional one
 ifdef CONFIG_CC_IS_GCC
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 59b6765d86b8..6b4f512f9e13 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -3020,6 +3020,24 @@ config RUST_OVERFLOW_CHECKS
 
 	  If unsure, say Y.
 
+config RUST_UNDEFINED_BEHAVIOR_CHECKS
+	bool "Undefined Behavior checks"
+	depends on RUST && RUSTC_VERSION >= 107900
+	help
+	  Enables rustc's `-Zub-checks` codegen option.
+
+	  This flag allows you to control whether additional runtime checks that
+	  detect some causes of Undefined Behavior at runtime will be emitted.
+	  When enabled, a Rust panic will occur if UB is detected.
+
+	  All checks are generated on a best-effort basis; even if there is a check
+	  implemented for some cause of Undefined Behavior, it may be possible for
+	  the check to not fire.
+
+	  Note that this will apply to all Rust code, including `core`.
+
+	  If unsure, say N.
+
 config RUST_BUILD_ASSERT_ALLOW
 	bool "Allow unoptimized build-time assertions"
 	depends on RUST
-- 
2.45.2

Re: [PATCH v2 11/13] kbuild: rust: add `rustc-version` support

[Miguel Ojeda]

On Tue, Jul 9, 2024 at 6:07 PM Miguel Ojeda <ojeda@kernel.org> wrote:
>
> +$(error-if,$(success,test -z "$(rustc-info)"),Sorry$(comma) this Rust compiler is not supported.)

Bah, this is broken, I just noticed in my CI that I didn't handle the
"Rust not installed" case.

Anyway, this patch (and the next one) are not important for the
series, I will just drop them and send them independently next cycle
to Kbuild instead. I should have done that anyway, even if they were
correct.

Cheers,
Miguel

Re: [PATCH v2 00/13] Support several Rust toolchain versions

[Miguel Ojeda]

On Tue, Jul 9, 2024 at 6:06 PM Miguel Ojeda <ojeda@kernel.org> wrote:
>
> A few things improved here and there, and rebased on top of `rust-next`.
>
> The changelog is attached to each patch.
>
> I kept the `Tested-by`s since most of the changes are on documentation
> or comments, though I did remove them on the patch that changed the most
> just in case (even for that one, I think Benno's and Andreas' setup
> would not have made a difference).
>
> I plan to put this series into `rust-next` very soon so that it goes
> into the merge window.

Applied into `rust-next` -- thanks everyone!

Cheers,
Miguel