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Date:   Thu, 28 Sep 2023 19:48:01 +0000
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Message-ID: <20230928194801.2278999-1-mmaurer@google.com>
Subject: [PATCH v3] rust: Respect HOSTCC when linking for host
From:   Matthew Maurer <mmaurer@google.com>
To:     Miguel Ojeda <ojeda@kernel.org>,
        Alex Gaynor <alex.gaynor@gmail.com>,
        Wedson Almeida Filho <wedsonaf@gmail.com>,
        Masahiro Yamada <masahiroy@kernel.org>,
        Nathan Chancellor <nathan@kernel.org>,
        Nick Desaulniers <ndesaulniers@google.com>
Cc:     Matthew Maurer <mmaurer@google.com>,
        Boqun Feng <boqun.feng@gmail.com>, Gary Guo <gary@garyguo.net>,
        "=?UTF-8?q?Bj=C3=B6rn=20Roy=20Baron?=" <bjorn3_gh@protonmail.com>,
        Benno Lossin <benno.lossin@proton.me>,
        Andreas Hindborg <a.hindborg@samsung.com>,
        Alice Ryhl <aliceryhl@google.com>,
        Nicolas Schier <nicolas@fjasle.eu>, Tom Rix <trix@redhat.com>,
        rust-for-linux@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-kbuild@vger.kernel.org, llvm@lists.linux.dev
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

Currently, rustc defaults to invoking `cc`, even if `HOSTCC` is defined,
resulting in build failures in hermetic environments where `cc` does not
exist. This includes both hostprogs and proc-macros.

Since we are setting the linker to `HOSTCC`, we set the linker flavor to
`gcc` explicitly. The linker-flavor selects both which linker to search
for if the linker is unset, and which kind of linker flags to pass.
Without this flag, `rustc` would attempt to determine which flags to
pass based on the name of the binary passed as `HOSTCC`. `gcc` is the
name of the linker-flavor used by `rustc` for all C compilers, including
both `gcc` and `clang`.

Signed-off-by: Matthew Maurer <mmaurer@google.com>
---
 rust/Makefile         | 2 ++
 scripts/Makefile.host | 2 ++
 2 files changed, 4 insertions(+)

diff --git a/rust/Makefile b/rust/Makefile
index 87958e864be0..da664d7aed51 100644
--- a/rust/Makefile
+++ b/rust/Makefile
@@ -383,6 +383,8 @@ $(obj)/exports_kernel_generated.h: $(obj)/kernel.o FORCE
 quiet_cmd_rustc_procmacro = $(RUSTC_OR_CLIPPY_QUIET) P $@
       cmd_rustc_procmacro = \
 	$(RUSTC_OR_CLIPPY) $(rust_common_flags) \
+		-Clinker-flavor=gcc -Clinker=$(HOSTCC) \
+		-Clink-args='$(subst ','\'',$(KBUILD_HOSTLDFLAGS))' \
 		--emit=dep-info=$(depfile) --emit=link=$@ --extern proc_macro \
 		--crate-type proc-macro \
 		--crate-name $(patsubst lib%.so,%,$(notdir $@)) $<
diff --git a/scripts/Makefile.host b/scripts/Makefile.host
index 8f7f842b54f9..08d83d9db31a 100644
--- a/scripts/Makefile.host
+++ b/scripts/Makefile.host
@@ -91,6 +91,8 @@ hostcxx_flags  = -Wp,-MMD,$(depfile) \
 # current working directory, which may be not accessible in the out-of-tree
 # modules case.
 hostrust_flags = --out-dir $(dir $@) --emit=dep-info=$(depfile) \
+		 -Clinker-flavor=gcc -Clinker=$(HOSTCC) \
+		 -Clink-args='$(call escsq,$(KBUILD_HOSTLDFLAGS))' \
                  $(KBUILD_HOSTRUSTFLAGS) $(HOST_EXTRARUSTFLAGS) \
                  $(HOSTRUSTFLAGS_$(target-stem))
 
-- 
2.42.0.582.g8ccd20d70d-goog