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Date:   Sat, 16 Sep 2023 17:53:03 +0000
To:     Finn Behrens <me@kloenk.dev>
From:   =?utf-8?Q?Bj=C3=B6rn_Roy_Baron?= <bjorn3_gh@protonmail.com>
Cc:     Matthew Maurer <mmaurer@google.com>,
        Miguel Ojeda <ojeda@kernel.org>,
        Alex Gaynor <alex.gaynor@gmail.com>,
        Wedson Almeida Filho <wedsonaf@gmail.com>,
        Masahiro Yamada <masahiroy@kernel.org>,
        Boqun Feng <boqun.feng@gmail.com>, Gary Guo <gary@garyguo.net>,
        Benno Lossin <benno.lossin@proton.me>,
        Andreas Hindborg <a.hindborg@samsung.com>,
        Alice Ryhl <aliceryhl@google.com>,
        Nathan Chancellor <nathan@kernel.org>,
        Nick Desaulniers <ndesaulniers@google.com>,
        Nicolas Schier <nicolas@fjasle.eu>,
        rust-for-linux@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-kbuild@vger.kernel.org
Subject: Re: [PATCH] rust: Respect HOSTCC when linking for host
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On Saturday, September 16th, 2023 at 18:52, Finn Behrens <me@kloenk.dev> wr=
ote:

>=20
> On 15 Sep 2023, at 19:28, Matthew Maurer wrote:
>=20
> > Currently, rustc defaults to invoking `cc`, even if `HOSTCC` is defined=
,
> > resulting in build failures in hermetic environments where `cc` does no=
t
> > exist. This includes both hostprogs and proc-macros.
> >
> > Since we are setting the linker to `HOSTCC`, we set the linker flavor t=
o
> > `gcc` explicitly.
> But as `HOSTCC` could also be clang, the linker flavor would then be wron=
g, would that create a problem?

Rustc uses the gcc linker flavor for clang too. There has been a proposal t=
o split it up, but I'm not sure of the status of that. In any case clang's =
cli is similar enough to gcc that it works fine to use the gcc linker flavo=
r.

> >
> > Signed-off-by: Matthew Maurer <mmaurer@google.com>
> > ---
> >  rust/Makefile         | 1 +
> >  scripts/Makefile.host | 1 +
> >  2 files changed, 2 insertions(+)
> >
> > diff --git a/rust/Makefile b/rust/Makefile
> > index 87958e864be0..2a2352638f11 100644
> > --- a/rust/Makefile
> > +++ b/rust/Makefile
> > @@ -383,6 +383,7 @@ $(obj)/exports_kernel_generated.h: $(obj)/kernel.o =
FORCE
> >  quiet_cmd_rustc_procmacro =3D $(RUSTC_OR_CLIPPY_QUIET) P $@
> >        cmd_rustc_procmacro =3D \
> >  =09$(RUSTC_OR_CLIPPY) $(rust_common_flags) \
> > +=09=09-C linker-flavor=3Dgcc -C linker=3D$(HOSTCC) \
> >  =09=09--emit=3Ddep-info=3D$(depfile) --emit=3Dlink=3D$@ --extern proc_=
macro \
> >  =09=09--crate-type proc-macro \
> >  =09=09--crate-name $(patsubst lib%.so,%,$(notdir $@)) $<
> > diff --git a/scripts/Makefile.host b/scripts/Makefile.host
> > index 8f7f842b54f9..0aa95a3af1c4 100644
> > --- a/scripts/Makefile.host
> > +++ b/scripts/Makefile.host
> > @@ -91,6 +91,7 @@ hostcxx_flags  =3D -Wp,-MMD,$(depfile) \
> >  # current working directory, which may be not accessible in the out-of=
-tree
> >  # modules case.
> >  hostrust_flags =3D --out-dir $(dir $@) --emit=3Ddep-info=3D$(depfile) =
\
> > +=09=09 -C linker-flavor=3Dgcc -C linker=3D$(HOSTCC) \
> >                   $(KBUILD_HOSTRUSTFLAGS) $(HOST_EXTRARUSTFLAGS) \
> >                   $(HOSTRUSTFLAGS_$(target-stem))
> >
> > --
> > 2.42.0.459.ge4e396fd5e-goog