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From:   Finn Behrens <me@kloenk.dev>
To:     =?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
Date:   Sat, 16 Sep 2023 20:06:47 +0200
Message-ID: <0561303E-2089-43FC-AA31-836C7BB844B7@kloenk.dev>
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On 16 Sep 2023, at 19:53, Bj=C3=B6rn Roy Baron wrote:

> On Saturday, September 16th, 2023 at 18:52, Finn Behrens <me@kloenk.dev=
> wrote:
>
>>
>> On 15 Sep 2023, at 19:28, Matthew Maurer wrote:
>>
>>> Currently, rustc defaults to invoking `cc`, even if `HOSTCC` is defin=
ed,
>>> 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.
>> But as `HOSTCC` could also be clang, the linker flavor would then be w=
rong, would that create a problem?
>
> Rustc uses the gcc linker flavor for clang too. There has been a propos=
al to split it up, but I'm not sure of the status of that. In any case cl=
ang's cli is similar enough to gcc that it works fine to use the gcc link=
er flavor.
>
In that case this looks very reasonable.

Second thing I noticed is that `HOSTCC` could be the wrong variable, and =
`HOSTLD` would make more sense as we look for the linker and not the gene=
ral C compiler.

>>>
>>> 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 \
>>>  	$(RUSTC_OR_CLIPPY) $(rust_common_flags) \
>>> +		-C linker-flavor=3Dgcc -C linker=3D$(HOSTCC) \
>>>  		--emit=3Ddep-info=3D$(depfile) --emit=3Dlink=3D$@ --extern proc_ma=
cro \
>>>  		--crate-type proc-macro \
>>>  		--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=
) \
>>> +		 -C linker-flavor=3Dgcc -C linker=3D$(HOSTCC) \
>>>                   $(KBUILD_HOSTRUSTFLAGS) $(HOST_EXTRARUSTFLAGS) \
>>>                   $(HOSTRUSTFLAGS_$(target-stem))
>>>
>>> --
>>> 2.42.0.459.ge4e396fd5e-goog