From: Segher Boessenkool <segher@kernel•crashing.org>
To: "Mukesh Kumar Chaurasiya (IBM)" <mkchauras@gmail•com>
Cc: maddy@linux•ibm.com, mpe@ellerman•id.au, npiggin@gmail•com,
chleroy@kernel•org, peterz@infradead•org, jpoimboe@kernel•org,
jbaron@akamai•com, aliceryhl@google•com, rostedt@goodmis•org,
ardb@kernel•org, sumit.semwal@linaro•org,
christian.koenig@amd•com, ojeda@kernel•org, boqun@kernel•org,
gary@garyguo•net, bjorn3_gh@protonmail•com, lossin@kernel•org,
a.hindborg@kernel•org, tmgross@umich•edu, dakr@kernel•org,
nathan@kernel•org, nick.desaulniers+lkml@gmail•com,
morbo@google•com, justinstitt@google•com, tamird@kernel•org,
arnd@arndb•de, nsc@kernel•org, simona.vetter@ffwll•ch,
linuxppc-dev@lists•ozlabs.org, linux-kernel@vger•kernel.org,
linux-media@vger•kernel.org, dri-devel@lists•freedesktop.org,
linaro-mm-sig@lists•linaro.org, rust-for-linux@vger•kernel.org,
llvm@lists•linux.dev, Link Mauve <linkmauve@linkmauve•fr>
Subject: Re: [PATCH V13 5/7] rust: Make __udivdi3() and __umoddi3() panic
Date: Fri, 24 Apr 2026 07:53:43 -0500 [thread overview]
Message-ID: <aetn16xR-uy7M7WA@gate> (raw)
In-Reply-To: <aetamPA_SsWcwC4M@gate>
On Fri, Apr 24, 2026 at 06:57:12AM -0500, Segher Boessenkool wrote:
> On Fri, Apr 24, 2026 at 06:54:05AM -0500, Segher Boessenkool wrote:
> > Hi!
> >
> > On Fri, Apr 24, 2026 at 11:17:40AM +0530, Mukesh Kumar Chaurasiya (IBM) wrote:
> > > 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.
> >
> > GCC uses calls to functions like even __addsi3 whenever the (sub-)target
> > does not implement some RTL, doesn't have a define_insn and the like for
> > it. When you write a new port you only *have* to implement a very few
> > things, the rest is done in libgcc (you might still have to write some
> > of that for your target, no free lunch etc.)
> >
> > 32-bit PowerPC has no instructions for 64-bit divisions, nor
> > instructions that help implementing it in software. It still very often
> > helps to hand-write machine code for it, it very easily can usually be
> > more than twice as fast for example (for example if the divisor is less
> > than half a word big, the common case -- it can be made tens of times
> > faster then).
> >
> > There can be many reasons why a GCC backend decides to call a libgcc
> > routine. For __udivdi3 on -m32 rs6000 you'll be good AFAICS :-)
> > (but poisoning functions like you do is a terrible idea in general!)
>
> Whoopsie, I forgot to mention:
>
> Approved for trunk.
Ugh, for some reason I thought this is a GCC patch :-(
Segher
next prev parent reply other threads:[~2026-04-24 12:54 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-04-24 5:47 [PATCH V13 0/7] Rust support for powerpc Mukesh Kumar Chaurasiya (IBM)
2026-04-24 5:47 ` [PATCH V13 1/7] rust: Fix "multiple candidates for rmeta dependency core" error Mukesh Kumar Chaurasiya (IBM)
2026-04-24 5:47 ` [PATCH V13 2/7] dma-resv: Fix undefined symbol when CONFIG_DMA_SHARED_BUFFER is disabled Mukesh Kumar Chaurasiya (IBM)
2026-04-24 7:56 ` Christian König
2026-04-24 8:06 ` Mukesh Kumar Chaurasiya
2026-04-24 8:25 ` Christian König
2026-04-24 8:34 ` Mukesh Kumar Chaurasiya
2026-04-24 8:44 ` Christian König
2026-04-24 5:47 ` [PATCH V13 3/7] powerpc/jump_label: adjust inline asm to be consistent Mukesh Kumar Chaurasiya (IBM)
2026-04-24 5:47 ` [PATCH V13 4/7] rust/powerpc: Set min rustc version for powerpc Mukesh Kumar Chaurasiya (IBM)
2026-04-24 5:47 ` [PATCH V13 5/7] rust: Make __udivdi3() and __umoddi3() panic Mukesh Kumar Chaurasiya (IBM)
2026-04-24 8:59 ` Arnd Bergmann
2026-04-24 9:14 ` David Laight
2026-04-24 9:43 ` Link Mauve
2026-04-24 10:20 ` Arnd Bergmann
2026-04-24 10:34 ` Miguel Ojeda
2026-04-24 10:26 ` Miguel Ojeda
2026-04-24 11:09 ` David Laight
2026-04-27 16:05 ` [Linaro-mm-sig] " Arnd Bergmann
2026-04-24 11:54 ` Segher Boessenkool
2026-04-24 11:57 ` Segher Boessenkool
2026-04-24 12:53 ` Segher Boessenkool [this message]
2026-04-24 12:43 ` Gary Guo
2026-04-26 7:52 ` Mukesh Kumar Chaurasiya
2026-04-26 14:20 ` Gary Guo
2026-04-26 22:04 ` David Laight
2026-04-27 13:04 ` Gary Guo
2026-04-24 5:47 ` [PATCH V13 6/7] rust: Add PowerPC support Mukesh Kumar Chaurasiya (IBM)
2026-04-24 5:47 ` [PATCH V13 7/7] powerpc: Enable Rust for ppc64le Mukesh Kumar Chaurasiya (IBM)
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