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References: <20221204231650.2604587-1-gary@garyguo.net>
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From:   Nick Desaulniers <ndesaulniers@google.com>
Date:   Mon, 5 Dec 2022 13:38:08 -0800
Message-ID: <CAKwvOdkDhxaURyV81Z6RNd4ekV8sGAckr7XDnU7rk_sWR23-8A@mail.gmail.com>
Subject: Re: [PATCH v2] rust: make compiler-builtin stubs non-global
To:     Gary Guo <gary@garyguo.net>
Cc:     Miguel Ojeda <ojeda@kernel.org>,
        Alex Gaynor <alex.gaynor@gmail.com>,
        Wedson Almeida Filho <wedsonaf@gmail.com>,
        Boqun Feng <boqun.feng@gmail.com>,
        =?UTF-8?Q?Bj=C3=B6rn_Roy_Baron?= <bjorn3_gh@protonmail.com>,
        rust-for-linux@vger.kernel.org, linux-kernel@vger.kernel.org
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On Sun, Dec 4, 2022 at 3:17 PM Gary Guo <gary@garyguo.net> wrote:
>
> Currently we define a number of stubs for compiler-builtin intrinsics
> that compiled libcore generates. The defined stubs are weak so they will
> not conflict with genuine implementation of these intrinsics, but their
> effect is global and will cause non-libcore code that accidently
> generate these intrinsics calls compile and bug on runtime.
>
> Instead of defining a stub that can affect all code, this patch uses
> objcopy's `--redefine-sym` flag to redirect these calls (from libcore
> only) to a prefixed version (e.g. redirect `__multi3` to `__rust_multi3`),
> so we can define panciking stubs that are only visible to libcore.
>
> This patch was previous discussed on GitHub.
> Link: https://github.com/Rust-for-Linux/linux/pull/779
>
> Signed-off-by: Gary Guo <gary@garyguo.net>

Thank you for addressing my feedback!

Link: https://lore.kernel.org/lkml/CAKwvOdkc0Qhwu=gfe1+H23TnAa6jnO6A3ZCO687dH6mSrATmDA@mail.gmail.com/
Suggested-by: Nick Desaulniers <ndesaulniers@google.com>
Acked-by: Nick Desaulniers <ndesaulniers@google.com>

>
> diff --git a/rust/Makefile b/rust/Makefile
> index ff70c4c916f8..aed6f7eca36f 100644
> --- a/rust/Makefile
> +++ b/rust/Makefile
> @@ -359,8 +359,22 @@ rust-analyzer:
>         $(Q)$(srctree)/scripts/generate_rust_analyzer.py $(srctree) $(objtree) \
>                 $(RUST_LIB_SRC) > $(objtree)/rust-project.json
>
> +redirect-intrinsics = \
> +       __eqsf2 __gesf2 __lesf2 __nesf2 __unordsf2 \
> +       __unorddf2 \
> +       __muloti4 __multi3 \
> +       __udivmodti4 __udivti3 __umodti3
> +
> +ifneq ($(or $(CONFIG_ARM64),$(and $(CONFIG_RISCV),$(CONFIG_64BIT))),)
> +       # These intrinsics are defined for ARM64 and RISCV64
> +       redirect-intrinsics += \
> +               __ashrti3 \
> +               __ashlti3 __lshrti3
> +endif
> +
>  $(obj)/core.o: private skip_clippy = 1
>  $(obj)/core.o: private skip_flags = -Dunreachable_pub
> +$(obj)/core.o: private rustc_objcopy = $(foreach sym,$(redirect-intrinsics),--redefine-sym $(sym)=__rust$(sym))
>  $(obj)/core.o: private rustc_target_flags = $(core-cfgs)
>  $(obj)/core.o: $(RUST_LIB_SRC)/core/src/lib.rs $(obj)/target.json FORCE
>         $(call if_changed_dep,rustc_library)
> diff --git a/rust/compiler_builtins.rs b/rust/compiler_builtins.rs
> index f8f39a3e6855..5f833dcca131 100644
> --- a/rust/compiler_builtins.rs
> +++ b/rust/compiler_builtins.rs
> @@ -28,7 +28,7 @@ macro_rules! define_panicking_intrinsics(
>      ($reason: tt, { $($ident: ident, )* }) => {
>          $(
>              #[doc(hidden)]
> -            #[no_mangle]
> +            #[export_name = concat!("__rust", stringify!($ident))]
>              pub extern "C" fn $ident() {
>                  panic!($reason);
>              }
> @@ -61,3 +61,6 @@ define_panicking_intrinsics!("`u128` should not be used", {
>      __udivti3,
>      __umodti3,
>  });
> +
> +// NOTE: if you are adding a new intrinsic is added here, you should also add it to
> +// `redirect-intrinsics` in `rust/Makefile`.
> --
> 2.34.1
>


-- 
Thanks,
~Nick Desaulniers