With the `RUSTC_VERSION_TEXT` rebuild support in place, now proc macros can depend on that instead of `core.o`. This means that both the `core` and `macros` crates can be built in parallel, and that touching `core.o` does not trigger a rebuild of the proc macros. This could be accomplished using the same approach as for `core` (i.e. depending directly on `include/config/RUSTC_VERSION_TEXT`). However, that is considered an implementation detail [1], and thus it is best to avoid it. Instead, let fixdep find a string that we explicitly write down in the source code for this purpose (like it is done for `include/linux/compiler-version.h`), which we can easily do (unlike for `core`) since this is our own source code. Suggested-by: Masahiro Yamada <masahiroy@xxxxxxxxxx> Link: https://lore.kernel.org/rust-for-linux/CAK7LNAQBG0nDupXSgAAk-6nOqeqGVkr3H1RjYaqRJ1OxmLm6xA@xxxxxxxxxxxxxx/ [1] Signed-off-by: Miguel Ojeda <ojeda@xxxxxxxxxx> --- rust/Makefile | 4 +--- rust/macros/lib.rs | 4 ++++ 2 files changed, 5 insertions(+), 3 deletions(-) diff --git a/rust/Makefile b/rust/Makefile index bb57a7c30f1a..4eae318f36ff 100644 --- a/rust/Makefile +++ b/rust/Makefile @@ -342,9 +342,7 @@ quiet_cmd_rustc_procmacro = $(RUSTC_OR_CLIPPY_QUIET) P $@ --crate-name $(patsubst lib%.so,%,$(notdir $@)) $< # Procedural macros can only be used with the `rustc` that compiled it. -# Therefore, to get `libmacros.so` automatically recompiled when the compiler -# version changes, we add `core.o` as a dependency (even if it is not needed). -$(obj)/libmacros.so: $(src)/macros/lib.rs $(obj)/core.o FORCE +$(obj)/libmacros.so: $(src)/macros/lib.rs FORCE +$(call if_changed_dep,rustc_procmacro) quiet_cmd_rustc_library = $(if $(skip_clippy),RUSTC,$(RUSTC_OR_CLIPPY_QUIET)) L $@ diff --git a/rust/macros/lib.rs b/rust/macros/lib.rs index 5be0cb9db3ee..a626b1145e5c 100644 --- a/rust/macros/lib.rs +++ b/rust/macros/lib.rs @@ -2,6 +2,10 @@ //! Crate for all kernel procedural macros. +// When fixdep scans this, it will find this string `CONFIG_RUSTC_VERSION_TEXT` +// and thus add a dependency on `include/config/RUSTC_VERSION_TEXT`, which is +// touched by Kconfig when the version string from the compiler changes. + #[macro_use] mod quote; mod concat_idents; -- 2.46.0
