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From:   Nick Desaulniers <ndesaulniers@google.com>
Date:   Fri, 6 Oct 2023 13:39:11 -0700
Message-ID: <CAKwvOdnWc6b9-XwC56ADXx6K2XCzrUPc_VMsAt=syKsp_b6ZSg@mail.gmail.com>
Subject: Re: [PATCH v4] rust: Respect HOSTCC when linking for host
To:     Matthew Maurer <mmaurer@google.com>
Cc:     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>,
        Boqun Feng <boqun.feng@gmail.com>, Gary Guo <gary@garyguo.net>,
        =?UTF-8?Q?Bj=C3=B6rn_Roy_Baron?= <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
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On Thu, Oct 5, 2023 at 2:41=E2=80=AFPM Matthew Maurer <mmaurer@google.com> =
wrote:
>
> 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>
> ---
>
> Edited to use escsq in both Makefiles, as per Masahiro Yamada's
> suggestion.

That looks better; thanks Matthew!
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>

>
>  rust/Makefile         | 2 ++
>  scripts/Makefile.host | 2 ++
>  2 files changed, 4 insertions(+)
>
> diff --git a/rust/Makefile b/rust/Makefile
> index 87958e864be0..2ddd821d9435 100644
> --- a/rust/Makefile
> +++ b/rust/Makefile
> @@ -383,6 +383,8 @@ $(obj)/exports_kernel_generated.h: $(obj)/kernel.o FO=
RCE
>  quiet_cmd_rustc_procmacro =3D $(RUSTC_OR_CLIPPY_QUIET) P $@
>        cmd_rustc_procmacro =3D \
>         $(RUSTC_OR_CLIPPY) $(rust_common_flags) \
> +               -Clinker-flavor=3Dgcc -Clinker=3D$(HOSTCC) \
> +               -Clink-args=3D'$(call escsq,$(KBUILD_HOSTLDFLAGS))' \
>                 --emit=3Ddep-info=3D$(depfile) --emit=3Dlink=3D$@ --exter=
n proc_macro \
>                 --crate-type proc-macro \
>                 --crate-name $(patsubst lib%.so,%,$(notdir $@)) $<
> diff --git a/scripts/Makefile.host b/scripts/Makefile.host
> index 8f7f842b54f9..08d83d9db31a 100644
> --- a/scripts/Makefile.host
> +++ b/scripts/Makefile.host
> @@ -91,6 +91,8 @@ hostcxx_flags  =3D -Wp,-MMD,$(depfile) \
>  # current working directory, which may be not accessible in the out-of-t=
ree
>  # modules case.
>  hostrust_flags =3D --out-dir $(dir $@) --emit=3Ddep-info=3D$(depfile) \
> +                -Clinker-flavor=3Dgcc -Clinker=3D$(HOSTCC) \
> +                -Clink-args=3D'$(call escsq,$(KBUILD_HOSTLDFLAGS))' \
>                   $(KBUILD_HOSTRUSTFLAGS) $(HOST_EXTRARUSTFLAGS) \
>                   $(HOSTRUSTFLAGS_$(target-stem))
>
> --
> 2.42.0.609.gbb76f46606-goog
>


--=20
Thanks,
~Nick Desaulniers