From ecab4115c44cc50fc7320bef9c19ac01ad43c785 Mon Sep 17 00:00:00 2001 From: Miguel Ojeda Date: Sat, 17 Feb 2024 01:26:37 +0100 Subject: kbuild: mark `rustc` (and others) invocations as recursive `rustc` (like Cargo) may take advantage of the jobserver at any time (e.g. for backend parallelism, or eventually frontend too). In the kernel, we call `rustc` with `-Ccodegen-units=1` (and `-Zthreads` is 1 so far), so we do not expect parallelism. However, in the upcoming Rust 1.76.0, a warning is emitted by `rustc` [1] when it cannot connect to the jobserver it was passed (in many cases, but not all: compiling and `--print sysroot` do, but `--version` does not). And given GNU Make always passes the jobserver in the environment variable (even when a line is deemed non-recursive), `rustc` will end up complaining about it (in particular in Make 4.3 where there is only the simple pipe jobserver style). One solution is to remove the jobserver from `MAKEFLAGS`. However, we can mark the lines with calls to `rustc` (and Cargo) as recursive, which looks simpler. This is being documented as a recommendation in `rustc` [2] and allows us to be ready for the time we may use parallelism inside `rustc` (potentially now, if a user passes `-Zthreads`). Thus do so. Similarly, do the same for `rustdoc` and `cargo` calls. Finally, there is one case that the solution does not cover, which is the `$(shell ...)` call we have. Thus, for that one, set an empty `MAKEFLAGS` environment variable. Link: https://github.com/rust-lang/rust/issues/120515 [1] Acked-by: Masahiro Yamada Link: https://github.com/rust-lang/rust/pull/121564 [2] Link: https://lore.kernel.org/r/20240217002638.57373-1-ojeda@kernel.org [ Reworded to add link to PR documenting the recommendation. ] Signed-off-by: Miguel Ojeda --- scripts/Makefile.host | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'scripts/Makefile.host') diff --git a/scripts/Makefile.host b/scripts/Makefile.host index 08d83d9db31a..3c17e6ba421c 100644 --- a/scripts/Makefile.host +++ b/scripts/Makefile.host @@ -156,7 +156,7 @@ quiet_cmd_host-rust = HOSTRUSTC $@ cmd_host-rust = \ $(HOSTRUSTC) $(hostrust_flags) --emit=link=$@ $< $(host-rust): $(obj)/%: $(src)/%.rs FORCE - $(call if_changed_dep,host-rust) + +$(call if_changed_dep,host-rust) targets += $(host-csingle) $(host-cmulti) $(host-cobjs) \ $(host-cxxmulti) $(host-cxxobjs) $(host-rust) -- cgit v1.2.3