Re: [PATCH] rust: bindgen: upgrade to 0.65.1

[Gary Guo]

On Tue, 13 Jun 2023 01:13:11 +0530
Aakash Sen Sharma <aakashsensharma@xxxxxxxxx> wrote:

> * Rationale:
> 
> Upgrades bindgen to code-generation for anonymous unions, structs, and enums [7]
> for LLVM-16 based toolchains.
> 
> The following upgrade also incorporates `noreturn` support from bindgen
> allowing us to remove useless `loop` calls which was placed as a
> workaround.
> 
> * Truncated build logs on using bindgen `v0.56.0` prior to LLVM-16 toolchain:
> 
> ```
> $ make rustdoc LLVM=1 CLIPPY=1 -j$(nproc)
>   RUSTC L rust/core.o
>   BINDGEN rust/bindings/bindings_generated.rs
>   BINDGEN rust/bindings/bindings_helpers_generated.rs
>   BINDGEN rust/uapi/uapi_generated.rs
> thread 'main' panicked at '"ftrace_branch_data_union_(anonymous_at__/_/include/linux/compiler_types_h_146_2)" is not a valid Ident', .../proc-macro2-1.0.24/src/fallback.rs:693:9
> ...
> thread 'main' panicked at '"ftrace_branch_data_union_(anonymous_at__/_/include/linux/compiler_types_h_146_2)" is not a valid Ident', .../proc-macro2-1.0.24/src/fallback.rs:693:9
> ...
> ```
> 
> * LLVM-16 Changes:
> 
> API changes [1] were introduced such that libclang would emit names like
> "(unnamed union at compiler_types.h:146:2)" for unnamed unions, structs, and
> enums whereas it previously returned an empty string.
> 
> * Bindgen Changes:
> 
> Bindgen `v0.56.0` on LLVM-16 based toolchains hence was unable to process the
> anonymous union in `include/linux/compiler_types` `struct ftrace_branch_data`
> and caused subsequent panics as the new `libclang` API emitted name was not
> being handled. The following issue was fixed in Bindgen `v0.62.0` [2].
> 
> Bindgen `v0.58.0` changed the flags `--whitelist-*` and `--blacklist-*`
> to `--allowlist-*` and `--blocklist-*` respectively [3].
> 
> Bindgen `v0.61.0` added support for `_Noreturn`, `[[noreturn]]`, `__attribute__((noreturn))` [4],
> hence the empty `loop`s used to circumvent bindgen returning `!` in place of `()`
> for noreturn attributes have been removed completely.
> 
> Bindgen `v0.61.0` also changed default functionality to bind `size_t` to `usize` [5] and
> added the `--no-size_t-is-usize` [5] flag to not bind `size_t` as `usize`.
> 
> Bindgen `v0.65.0` removed `--size_t-is-usize` flag [6].
> 
> Link: https://github.com/llvm/llvm-project/commit/19e984ef8f49bc3ccced15621989fa9703b2cd5b [1]
> Link: https://github.com/rust-lang/rust-bindgen/pull/2319 [2]
> Link: https://github.com/rust-lang/rust-bindgen/pull/1990 [3]
> Link: https://github.com/rust-lang/rust-bindgen/issues/2094 [4]
> Link: https://github.com/rust-lang/rust-bindgen/commit/cc78b6fdb6e829e5fb8fa1639f2182cb49333569 [5]
> Link: https://github.com/rust-lang/rust-bindgen/pull/2408 [6]
> Closes: https://github.com/Rust-for-Linux/linux/issues/1013 [7]
> Signed-off-by: Aakash Sen Sharma <aakashsensharma@xxxxxxxxx>

Reviewed-by: Gary Guo <gary@xxxxxxxxxxx>

> ---
>  Documentation/process/changes.rst |  2 +-
>  rust/Makefile                     |  6 +++---
>  rust/helpers.c                    | 13 ++++++-------
>  rust/kernel/lib.rs                |  3 ---
>  scripts/min-tool-version.sh       |  2 +-
>  5 files changed, 11 insertions(+), 15 deletions(-)
> 
> diff --git a/Documentation/process/changes.rst b/Documentation/process/changes.rst
> index ef540865ad22..5f21c4c6cf5c 100644
> --- a/Documentation/process/changes.rst
> +++ b/Documentation/process/changes.rst
> @@ -32,7 +32,7 @@ you probably needn't concern yourself with pcmciautils.
>  GNU C                  5.1              gcc --version
>  Clang/LLVM (optional)  11.0.0           clang --version
>  Rust (optional)        1.62.0           rustc --version
> -bindgen (optional)     0.56.0           bindgen --version
> +bindgen (optional)     0.65.1           bindgen --version
>  GNU make               3.82             make --version
>  bash                   4.2              bash --version
>  binutils               2.25             ld -v
> diff --git a/rust/Makefile b/rust/Makefile
> index f88d108fbef0..c187c6f3a384 100644
> --- a/rust/Makefile
> +++ b/rust/Makefile
> @@ -279,7 +279,7 @@ quiet_cmd_bindgen = BINDGEN $@
>  	$(BINDGEN) $< $(bindgen_target_flags) \
>  		--use-core --with-derive-default --ctypes-prefix core::ffi --no-layout-tests \
>  		--no-debug '.*' \
> -		--size_t-is-usize -o $@ -- $(bindgen_c_flags_final) -DMODULE \
> +		-o $@ -- $(bindgen_c_flags_final) -DMODULE \
>  		$(bindgen_target_cflags) $(bindgen_target_extra)
> 
>  $(obj)/bindings/bindings_generated.rs: private bindgen_target_flags = \
> @@ -293,8 +293,8 @@ $(obj)/bindings/bindings_generated.rs: $(src)/bindings/bindings_helper.h \
>  # given it is `libclang`; but for consistency, future Clang changes and/or
>  # a potential future GCC backend for `bindgen`, we disable it too.
>  $(obj)/bindings/bindings_helpers_generated.rs: private bindgen_target_flags = \
> -    --blacklist-type '.*' --whitelist-var '' \
> -    --whitelist-function 'rust_helper_.*'
> +    --blocklist-type '.*' --allowlist-var '' \
> +    --allowlist-function 'rust_helper_.*'
>  $(obj)/bindings/bindings_helpers_generated.rs: private bindgen_target_cflags = \
>      -I$(objtree)/$(obj) -Wno-missing-prototypes -Wno-missing-declarations
>  $(obj)/bindings/bindings_helpers_generated.rs: private bindgen_target_extra = ; \
> diff --git a/rust/helpers.c b/rust/helpers.c
> index 121583282976..98d9ef47225b 100644
> --- a/rust/helpers.c
> +++ b/rust/helpers.c
> @@ -122,19 +122,18 @@ void rust_helper_put_task_struct(struct task_struct *t)
>  EXPORT_SYMBOL_GPL(rust_helper_put_task_struct);
> 
>  /*
> - * We use `bindgen`'s `--size_t-is-usize` option to bind the C `size_t` type
> - * as the Rust `usize` type, so we can use it in contexts where Rust
> - * expects a `usize` like slice (array) indices. `usize` is defined to be
> - * the same as C's `uintptr_t` type (can hold any pointer) but not
> - * necessarily the same as `size_t` (can hold the size of any single
> + * `bindgen` binds the C `size_t` type the Rust `usize` type, so we can
> + * use it in contexts where Rust expects a `usize` like slice (array) indices.
> + * `usize` is defined to be the same as C's `uintptr_t` type (can hold any pointer)
> + * but not necessarily the same as `size_t` (can hold the size of any single
>   * object). Most modern platforms use the same concrete integer type for
>   * both of them, but in case we find ourselves on a platform where
>   * that's not true, fail early instead of risking ABI or
>   * integer-overflow issues.
>   *
>   * If your platform fails this assertion, it means that you are in
> - * danger of integer-overflow bugs (even if you attempt to remove
> - * `--size_t-is-usize`). It may be easiest to change the kernel ABI on
> + * danger of integer-overflow bugs (even if you attempt to add
> + * `--no-size_t-is-usize`). It may be easiest to change the kernel ABI on
>   * your platform such that `size_t` matches `uintptr_t` (i.e., to increase
>   * `size_t`, because `uintptr_t` has to be at least as big as `size_t`).
>   */
> diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs
> index ee27e10da479..1b0dcf03b9c2 100644
> --- a/rust/kernel/lib.rs
> +++ b/rust/kernel/lib.rs
> @@ -95,7 +95,4 @@ fn panic(info: &core::panic::PanicInfo<'_>) -> ! {
>      pr_emerg!("{}\n", info);
>      // SAFETY: FFI call.
>      unsafe { bindings::BUG() };
> -    // Bindgen currently does not recognize `__noreturn` so `BUG` returns `()`
> -    // instead of `!`. See <https://github.com/rust-lang/rust-bindgen/issues/2094>.
> -    loop {}
>  }
> diff --git a/scripts/min-tool-version.sh b/scripts/min-tool-version.sh
> index 20d483ec6f5f..5b80c5d3a9f8 100755
> --- a/scripts/min-tool-version.sh
> +++ b/scripts/min-tool-version.sh
> @@ -30,7 +30,7 @@ rustc)
>  	echo 1.62.0
>  	;;
>  bindgen)
> -	echo 0.56.0
> +	echo 0.65.1
>  	;;
>  *)
>  	echo "$1: unknown tool" >&2
> --
> 2.40.1
>