From: David Laight <david.laight.linux@gmail•com>
To: "Gary Guo" <gary@garyguo•net>
Cc: "Mukesh Kumar Chaurasiya" <mkchauras@gmail•com>,
<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>,
<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: Sun, 26 Apr 2026 23:04:08 +0100 [thread overview]
Message-ID: <20260426230408.489c68c3@pumpkin> (raw)
In-Reply-To: <DI35IFD8M019.2WGRH5ADW6NOG@garyguo.net>
On Sun, 26 Apr 2026 15:20:31 +0100
"Gary Guo" <gary@garyguo•net> wrote:
> On Sun Apr 26, 2026 at 8:52 AM BST, Mukesh Kumar Chaurasiya wrote:
> > 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@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.
>
> Sorry. I quoted the wrong part. I was asking if compiling libcore with O2 gets
> rid of its use of the builtins, as that's what the change this commit is for.
>
> Formatting of u64 will be needed, so we should make sure that these works as
> intended.
This code (from nolibc) will convert u64 to ascii in any base:
#define _U64TOA_RECIP(base) ((base) & 1 ? ~0ull / (base) : (1ull << 63) / ((base) / 2))
static int _u64toa_base(u64 in, char *buffer, unsigned int base, u64 recip)
{
unsigned int digits = 0;
unsigned int dig;
u64 q;
char *p;
/* Generate least significant digit first */
do {
#if defined(__SIZEOF_INT128__) && !defined(__mips__)
q = ((unsigned __int128)in * recip) >> 64;
#else
u64 p = (u32)in * (recip >> 32);
q = (in >> 32) * (recip >> 32) + (p >> 32);
p = (u32)p + (in >> 32) * (u32)recip;
q += p >> 32;
#endif
dig = in - q * base;
/* Correct for any rounding errors */
if (dig >= base) {
dig -= base;
q++;
}
if (dig > 9)
dig += 'a' - '0' - 10;
buffer[digits++] = '0' + dig;
} while ((in = q));
buffer[digits] = 0;
/* Order reverse to result */
for (p = buffer + digits - 1; p > buffer; buffer++, p--) {
dig = *buffer;
*buffer = *p;
*p = dig;
}
return digits;
}
int u64toa_r(u64 in, char *buffer)
{
return _u64toa_base(in, buffer, 10, _U64TOA_RECIP(10));
}
Not hard to do without any divides at all.
David
next prev parent reply other threads:[~2026-04-26 22:04 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
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 [this message]
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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