linux-kernel - Re: [PATCH v2] rust: Respect HOSTCC when linking for host

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Date:   Tue, 19 Sep 2023 13:02:45 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Matthew Maurer <mmaurer@...gle.com>
Cc:     Miguel Ojeda <ojeda@...nel.org>,
        Alex Gaynor <alex.gaynor@...il.com>,
        Wedson Almeida Filho <wedsonaf@...il.com>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Boqun Feng <boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>,
        Björn Roy Baron <bjorn3_gh@...tonmail.com>,
        Benno Lossin <benno.lossin@...ton.me>,
        Andreas Hindborg <a.hindborg@...sung.com>,
        Alice Ryhl <aliceryhl@...gle.com>,
        Nathan Chancellor <nathan@...nel.org>,
        Nicolas Schier <nicolas@...sle.eu>,
        rust-for-linux@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-kbuild@...r.kernel.org
Subject: Re: [PATCH v2] rust: Respect HOSTCC when linking for host

On Tue, Sep 19, 2023 at 12:44 PM Nick Desaulniers
<ndesaulniers@...gle.com> wrote:
>
> On Mon, Sep 18, 2023 at 4:44 PM Matthew Maurer <mmaurer@...gle.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.
> >
> > Signed-off-by: Matthew Maurer <mmaurer@...gle.com>
> > ---
> >
> > Updated the patch to reflect Nick's comment that KBUILD_HOSTLDFLAGS
> > should be respected as well.
> >
> > I did not switch it to use HOSTLD for two reasons:
> > * That variable is not globally defined - it is only available in two
> >   subdirectories of tools/
> > * C host scripts are linked by HOSTCC as well, even when linking a
> >   collection of object files. It *prints* HOSTLD, but invokes HOSTCC.
> >   See scripts/Makefile.host cmd_host-cmulti for an example.
>
> Sure, that makes sense to me, thanks for pointing that out.
>
> >
> >  rust/Makefile         | 4 ++++
> >  scripts/Makefile.host | 4 ++++
> >  2 files changed, 8 insertions(+)
> >
> > diff --git a/rust/Makefile b/rust/Makefile
> > index 87958e864be0..b60b7eb8c5a0 100644
> > --- a/rust/Makefile
> > +++ b/rust/Makefile
> > @@ -380,9 +380,13 @@ $(obj)/exports_bindings_generated.h: $(obj)/bindings.o FORCE
> >  $(obj)/exports_kernel_generated.h: $(obj)/kernel.o FORCE
> >         $(call if_changed,exports)
> >
> > +KBUILD_HOSTLDFLAGS_SQ = '$(subst ','\'',$(KBUILD_HOSTLDFLAGS))'
>
> I don't think we need to do this kind of escaping. If a linker flag is
> passed to the linker directly as the driver has spaces such as `-z
> relro`, if it is instead passed to the compiler as the driver will not
> contain spaces (`-Wl,-z,relro`). As such, I don't think we need this
> escaping (famous last words).  Mind submitting a v3 without it?

Thanks for clarifying off list that:
```
It's not escaping the spaces, it's escaping any quotes
example: -Clink-args='-Wl,-z,relro -Wl,-linker-plugin-lto'
Without the quote, the second one would go to rustc rather than the linker
```

Sorry for misunderstanding what exactly we were escaping here and why;
thanks for implementing my suggestion of passing along
KBUILD_HOSTLDFLAGS though.  That will avoid issues for Android
downstream.

Reviewed-by: Nick Desaulniers <ndesaulniers@...gle.com>

>
> > +
> >  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=$(KBUILD_HOSTLDFLAGS_SQ) \
> >                 --emit=dep-info=$(depfile) --emit=link=$@ --extern proc_macro \
> >                 --crate-type proc-macro \
> >                 --crate-name $(patsubst lib%.so,%,$(notdir $@)) $<
> > diff --git a/scripts/Makefile.host b/scripts/Makefile.host
> > index 8f7f842b54f9..dc0410cae5ca 100644
> > --- a/scripts/Makefile.host
> > +++ b/scripts/Makefile.host
> > @@ -87,10 +87,14 @@ hostcxx_flags  = -Wp,-MMD,$(depfile) \
> >                   $(KBUILD_HOSTCXXFLAGS) $(HOST_EXTRACXXFLAGS) \
> >                   $(HOSTCXXFLAGS_$(target-stem).o)
> >
> > +KBUILD_HOSTLDFLAGS_SQ = '$(subst ','\'',$(KBUILD_HOSTLDFLAGS))'
> > +
> >  # `--out-dir` is required to avoid temporaries being created by `rustc` in the
> >  # 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=$(HOSTCC) \
> > +                -Clink-args=$(KBUILD_HOSTLDFLAGS_SQ) \
> >                   $(KBUILD_HOSTRUSTFLAGS) $(HOST_EXTRARUSTFLAGS) \
> >                   $(HOSTRUSTFLAGS_$(target-stem))
> >
> > --
> > 2.42.0.459.ge4e396fd5e-goog
> >
>
>
> --
> Thanks,
> ~Nick Desaulniers



-- 
Thanks,
~Nick Desaulniers