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

[Mukesh Kumar Chaurasiya]

On Fri, Apr 24, 2026 at 01:43:43PM +0100, Gary Guo wrote:
> On Fri Apr 24, 2026 at 6:47 AM BST, Mukesh Kumar Chaurasiya (IBM) wrote:
> > From: Link Mauve <linkmauve at 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.
> >
> > 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.
> 
> Can we always build libcore with `-C opt-level=2` even if
> `CONFIG_CC_OPTIMIZE_FOR_SIZE` is specified? It feels like a better fix than
> stubbing things out.
> 
> Best,
> Gary
> 
The issue is not coming from libcore itself. It's the driver that's
causing this.

Regards,
Mukesh
> >
> > Signed-off-by: Link Mauve <linkmauve at linkmauve.fr>
> > Signed-off-by: Mukesh Kumar Chaurasiya (IBM) <mkchauras at 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`.
>