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authorMiguel Ojeda <ojeda@kernel.org>2024-02-17 01:26:37 +0100
committerMiguel Ojeda <ojeda@kernel.org>2024-02-29 22:16:38 +0100
commitecab4115c44cc50fc7320bef9c19ac01ad43c785 (patch)
tree0b66eb9e69599a4eb0b8ed60ef91f91fae2442d5 /scripts/Makefile.host
parente944171070b65521c0513c01c56174ec8fd7d249 (diff)
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 <masahiroy@kernel.org> 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 <ojeda@kernel.org>
Diffstat (limited to 'scripts/Makefile.host')
-rw-r--r--scripts/Makefile.host2
1 files changed, 1 insertions, 1 deletions
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)