From ecaa6ddff2fd843c0236a931bcc62bf239956617 Mon Sep 17 00:00:00 2001 From: Gary Guo Date: Thu, 10 Nov 2022 17:41:37 +0100 Subject: [PATCH] rust: add `build_error` crate The `build_error` crate provides a function `build_error` which will panic at compile-time if executed in const context and, by default, will cause a build error if not executed at compile time and the optimizer does not optimise away the call. The `CONFIG_RUST_BUILD_ASSERT_ALLOW` kernel option allows to relax the default build failure and convert it to a runtime check. If the runtime check fails, `panic!` will be called. Its functionality will be exposed to users as a couple macros in the `kernel` crate in the following patch, thus some documentation here refers to them for simplicity. Signed-off-by: Gary Guo Reviewed-by: Wei Liu [Reworded, adapted for upstream and applied latest changes] Signed-off-by: Miguel Ojeda --- lib/Kconfig.debug | 16 ++++++++++++++++ rust/Makefile | 22 +++++++++++++++++----- rust/build_error.rs | 31 +++++++++++++++++++++++++++++++ rust/exports.c | 5 +++++ scripts/generate_rust_analyzer.py | 8 +++++++- 5 files changed, 76 insertions(+), 6 deletions(-) create mode 100644 rust/build_error.rs diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug index 29280072dc0e..452c9f06c2bc 100644 --- a/lib/Kconfig.debug +++ b/lib/Kconfig.debug @@ -2801,6 +2801,22 @@ config RUST_OVERFLOW_CHECKS If unsure, say Y. +config RUST_BUILD_ASSERT_ALLOW + bool "Allow unoptimized build-time assertions" + depends on RUST + help + Controls how are `build_error!` and `build_assert!` handled during build. + + If calls to them exist in the binary, it may indicate a violated invariant + or that the optimizer failed to verify the invariant during compilation. + + This should not happen, thus by default the build is aborted. However, + as an escape hatch, you can choose Y here to ignore them during build + and let the check be carried at runtime (with `panic!` being called if + the check fails). + + If unsure, say N. + endmenu # "Rust" source "Documentation/Kconfig" diff --git a/rust/Makefile b/rust/Makefile index 7700d3853404..ff70c4c916f8 100644 --- a/rust/Makefile +++ b/rust/Makefile @@ -19,6 +19,12 @@ obj-$(CONFIG_RUST) += alloc.o bindings.o kernel.o always-$(CONFIG_RUST) += exports_alloc_generated.h exports_bindings_generated.h \ exports_kernel_generated.h +ifdef CONFIG_RUST_BUILD_ASSERT_ALLOW +obj-$(CONFIG_RUST) += build_error.o +else +always-$(CONFIG_RUST) += build_error.o +endif + obj-$(CONFIG_RUST) += exports.o # Avoids running `$(RUSTC)` for the sysroot when it may not be available. @@ -108,7 +114,7 @@ rustdoc-alloc: $(src)/alloc/lib.rs rustdoc-core rustdoc-compiler_builtins FORCE $(call if_changed,rustdoc) rustdoc-kernel: private rustc_target_flags = --extern alloc \ - --extern macros=$(objtree)/$(obj)/libmacros.so \ + --extern build_error --extern macros=$(objtree)/$(obj)/libmacros.so \ --extern bindings rustdoc-kernel: $(src)/kernel/lib.rs rustdoc-core rustdoc-macros \ rustdoc-compiler_builtins rustdoc-alloc $(obj)/libmacros.so \ @@ -126,6 +132,9 @@ quiet_cmd_rustc_test_library = RUSTC TL $< -L$(objtree)/$(obj)/test \ --crate-name $(subst rusttest-,,$(subst rusttestlib-,,$@)) $< +rusttestlib-build_error: $(src)/build_error.rs rusttest-prepare FORCE + $(call if_changed,rustc_test_library) + rusttestlib-macros: private rustc_target_flags = --extern proc_macro rusttestlib-macros: private rustc_test_library_proc = yes rusttestlib-macros: $(src)/macros/lib.rs rusttest-prepare FORCE @@ -216,9 +225,9 @@ rusttest-macros: $(src)/macros/lib.rs rusttest-prepare FORCE $(call if_changed,rustdoc_test) rusttest-kernel: private rustc_target_flags = --extern alloc \ - --extern macros --extern bindings + --extern build_error --extern macros --extern bindings rusttest-kernel: $(src)/kernel/lib.rs rusttest-prepare \ - rusttestlib-macros rusttestlib-bindings FORCE + rusttestlib-build_error rusttestlib-macros rusttestlib-bindings FORCE $(call if_changed,rustc_test) $(call if_changed,rustc_test_library) @@ -366,6 +375,9 @@ $(obj)/alloc.o: private rustc_target_flags = $(alloc-cfgs) $(obj)/alloc.o: $(src)/alloc/lib.rs $(obj)/compiler_builtins.o FORCE $(call if_changed_dep,rustc_library) +$(obj)/build_error.o: $(src)/build_error.rs $(obj)/compiler_builtins.o FORCE + $(call if_changed_dep,rustc_library) + $(obj)/bindings.o: $(src)/bindings/lib.rs \ $(obj)/compiler_builtins.o \ $(obj)/bindings/bindings_generated.rs \ @@ -373,8 +385,8 @@ $(obj)/bindings.o: $(src)/bindings/lib.rs \ $(call if_changed_dep,rustc_library) $(obj)/kernel.o: private rustc_target_flags = --extern alloc \ - --extern macros --extern bindings -$(obj)/kernel.o: $(src)/kernel/lib.rs $(obj)/alloc.o \ + --extern build_error --extern macros --extern bindings +$(obj)/kernel.o: $(src)/kernel/lib.rs $(obj)/alloc.o $(obj)/build_error.o \ $(obj)/libmacros.so $(obj)/bindings.o FORCE $(call if_changed_dep,rustc_library) diff --git a/rust/build_error.rs b/rust/build_error.rs new file mode 100644 index 000000000000..fa24eeef9929 --- /dev/null +++ b/rust/build_error.rs @@ -0,0 +1,31 @@ +// SPDX-License-Identifier: GPL-2.0 + +//! Build-time error. +//! +//! This crate provides a [const function][const-functions] `build_error`, which will panic in +//! compile-time if executed in [const context][const-context], and will cause a build error +//! if not executed at compile time and the optimizer does not optimise away the call. +//! +//! It is used by `build_assert!` in the kernel crate, allowing checking of +//! conditions that could be checked statically, but could not be enforced in +//! Rust yet (e.g. perform some checks in [const functions][const-functions], but those +//! functions could still be called in the runtime). +//! +//! For details on constant evaluation in Rust, please see the [Reference][const-eval]. +//! +//! [const-eval]: https://doc.rust-lang.org/reference/const_eval.html +//! [const-functions]: https://doc.rust-lang.org/reference/const_eval.html#const-functions +//! [const-context]: https://doc.rust-lang.org/reference/const_eval.html#const-context + +#![no_std] + +/// Panics if executed in [const context][const-context], or triggers a build error if not. +/// +/// [const-context]: https://doc.rust-lang.org/reference/const_eval.html#const-context +#[inline(never)] +#[cold] +#[export_name = "rust_build_error"] +#[track_caller] +pub const fn build_error(msg: &'static str) -> ! { + panic!("{}", msg); +} diff --git a/rust/exports.c b/rust/exports.c index bb7cc64cecd0..83e2a7070cae 100644 --- a/rust/exports.c +++ b/rust/exports.c @@ -19,3 +19,8 @@ #include "exports_alloc_generated.h" #include "exports_bindings_generated.h" #include "exports_kernel_generated.h" + +// For modules using `rust/build_error.rs`. +#ifdef CONFIG_RUST_BUILD_ASSERT_ALLOW +EXPORT_SYMBOL_RUST_GPL(rust_build_error); +#endif diff --git a/scripts/generate_rust_analyzer.py b/scripts/generate_rust_analyzer.py index 75bb611bd751..ecc7ea9a4dcf 100755 --- a/scripts/generate_rust_analyzer.py +++ b/scripts/generate_rust_analyzer.py @@ -67,6 +67,12 @@ def generate_crates(srctree, objtree, sysroot_src): ) crates[-1]["proc_macro_dylib_path"] = "rust/libmacros.so" + append_crate( + "build_error", + srctree / "rust" / "build_error.rs", + ["core", "compiler_builtins"], + ) + append_crate( "bindings", srctree / "rust"/ "bindings" / "lib.rs", @@ -78,7 +84,7 @@ def generate_crates(srctree, objtree, sysroot_src): append_crate( "kernel", srctree / "rust" / "kernel" / "lib.rs", - ["core", "alloc", "macros", "bindings"], + ["core", "alloc", "macros", "build_error", "bindings"], cfg=cfg, ) crates[-1]["source"] = {