Re: [PATCH V13 5/7] rust: Make __udivdi3() and __umoddi3() panic

[David Laight <david.laight.linux@gmail.com>]

On Fri, 24 Apr 2026 11:17:40 +0530
"Mukesh Kumar Chaurasiya (IBM)" <mkchauras@gmail.com> wrote:

> From: Link Mauve <linkmauve@linkmauve.fr>
> 
> The core crate currently depends on these two functions for i64/u64/
> i128/u128/core::time::Duration formatting, but we shouldn’t use that in
> the kernel so let’s panic if they are ever called.

Ugg.
Surely you can make it a link-time failure?
Or change the underlying code to avoid the divide.

	David

> 
> This doesn’t yet fix drm_panic_qr.rs, which also uses __udivdi3 when
> CONFIG_CC_OPTIMIZE_FOR_SIZE=y, but at least makes the rest of the kernel
> build on PPC32.
> 
> Signed-off-by: Link Mauve <linkmauve@linkmauve.fr>
> Signed-off-by: Mukesh Kumar Chaurasiya (IBM) <mkchauras@gmail.com>
> ---
>  rust/Makefile             | 4 ++++
>  rust/compiler_builtins.rs | 6 ++++++
>  2 files changed, 10 insertions(+)
> 
> diff --git a/rust/Makefile b/rust/Makefile
> index 2a5428a5503d..ee11fba7a03d 100644
> --- a/rust/Makefile
> +++ b/rust/Makefile
> @@ -616,6 +616,10 @@ ifneq ($(or $(CONFIG_ARM64),$(and $(CONFIG_RISCV),$(CONFIG_64BIT))),)
>  		__ashrti3 \
>  		__ashlti3 __lshrti3
>  endif
> +ifdef CONFIG_PPC32
> +	redirect-intrinsics += \
> +		__udivdi3 __umoddi3
> +endif
>  
>  ifdef CONFIG_MODVERSIONS
>  cmd_gendwarfksyms = $(if $(skip_gendwarfksyms),, \
> diff --git a/rust/compiler_builtins.rs b/rust/compiler_builtins.rs
> index dd16c1dc899c..fc6b54636dd5 100644
> --- a/rust/compiler_builtins.rs
> +++ b/rust/compiler_builtins.rs
> @@ -97,5 +97,11 @@ pub extern "C" fn $ident() {
>      __aeabi_uldivmod,
>  });
>  
> +#[cfg(target_arch = "powerpc")]
> +define_panicking_intrinsics!("`u64` division/modulo should not be used", {
> +    __udivdi3,
> +    __umoddi3,
> +});
> +
>  // NOTE: if you are adding a new intrinsic here, you should also add it to
>  // `redirect-intrinsics` in `rust/Makefile`.