Re: git: b80ea452375f - main - LinuxKPI: implement mul_u64_u64_div_u64()

On 8/17/23 20:21, Bjoern A. Zeeb wrote:
> The branch main has been updated by bz:
> 
> URL: https://cgit.FreeBSD.org/src/commit/?id=b80ea452375f52a3ab7d82a9aef10da0d89985d9
> 
> commit b80ea452375f52a3ab7d82a9aef10da0d89985d9
> Author:     Bjoern A. Zeeb <bz@FreeBSD.org>
> AuthorDate: 2023-05-16 20:55:00 +0000
> Commit:     Bjoern A. Zeeb <bz@FreeBSD.org>
> CommitDate: 2023-08-18 01:20:39 +0000
> 
>      LinuxKPI: implement mul_u64_u64_div_u64()
>      
>      Implement mul_u64_u64_div_u64() for an updated iwlwifi driver (though
>      we do not yet use it there; it is used for in-kernel ptp on wifi).
>      
>      Sponsored by:   The FreeBSD Foundation
>      Submitted by:   cperciva
>      MFC after:      10 days
>      Reviewed by:    cperciva, dwmalone
>      Differential Revision: https://reviews.freebsd.org/D40120

This broke buildkernel on multiple architectures, it seems: 
https://ci.freebsd.org/tinderbox/

I've confirmed that reverting this commit fixes it. I'd be lying if I 
claimed to understand what's going on:

23:09:45 In file included from /usr/src/sys/dev/cxgbe/iw_cxgbe/device.c:39:
23:09:45 In file included from 
/usr/src/sys/compat/linuxkpi/common/include/linux/module.h:41:
23:09:45 In file included from 
/usr/src/sys/compat/linuxkpi/common/include/linux/kobject.h:34:
23:09:45 In file included from 
/usr/src/sys/compat/linuxkpi/common/include/linux/kernel.h:48:
23:09:45 In file included from 
/usr/src/sys/compat/linuxkpi/common/include/linux/sched.h:43:
23:09:45 In file included from 
/usr/src/sys/compat/linuxkpi/common/include/linux/hrtimer.h:32:
23:09:45 /usr/src/sys/compat/linuxkpi/common/include/linux/ktime.h:34:2: 
error: embedding a #include directive within macro arguments is not 
supported
23:09:45 #include <linux/jiffies.h>
23:09:45  ^
23:09:45 
/usr/src/sys/compat/linuxkpi/common/include/linux/math64.h:151:2: note: 
expansion of macro 'KASSERT' requested here
23:09:45         KASSERT(rem < z, ("%s: rem %ju >= z %ju\n", __func__,
23:09:45         ^


> ---
>   sys/compat/linuxkpi/common/include/linux/math64.h | 48 +++++++++++++++++++++++
>   1 file changed, 48 insertions(+)
> 
> diff --git a/sys/compat/linuxkpi/common/include/linux/math64.h b/sys/compat/linuxkpi/common/include/linux/math64.h
> index 1b00fd71e69f..e4ddce5b823e 100644
> --- a/sys/compat/linuxkpi/common/include/linux/math64.h
> +++ b/sys/compat/linuxkpi/common/include/linux/math64.h
> @@ -106,6 +106,54 @@ mul_u64_u32_div(uint64_t x, uint32_t y, uint32_t div)
>   	return ((x / div) * y + (rem * y) / div);
>   }
>   
> +static inline uint64_t
> +mul_u64_u64_div_u64(uint64_t x, uint64_t y, uint64_t z)
> +{
> +	uint64_t res, rem;
> +	uint64_t x1, y1, y1z;
> +
> +	res = rem = 0;
> +	x1 = x;
> +	y1z = y / z;
> +	y1 = y - y1z * z;
> +
> +	/*
> +	 * INVARIANT: x * y = res * z + rem + (y1 + y1z * z) * x1
> +	 * INVARIANT: y1 < z
> +	 * INVARIANT: rem < z
> +	 */
> +	while (x1 > 0) {
> +		/* Handle low bit. */
> +		if (x1 & 1) {
> +			x1 &= ~1;
> +			res += y1z;
> +			rem += y1;
> +			if ((rem < y1) || (rem >= z)) {
> +				res += 1;
> +				rem -= z;
> +			}
> +		}
> +
> +		/* Shift x1 right and (y1 + y1z * z) left */
> +		x1 >>= 1;
> +		if ((y1 * 2 < y1) || (y1 * 2 >= z)) {
> +			y1z = y1z * 2 + 1;
> +			y1 = y1 * 2 - z;
> +		} else {
> +			y1z *= 2;
> +			y1 *= 2;
> +		}
> +	}
> +
> +	KASSERT(res * z + rem == x * y, ("%s: res %ju * z %ju + rem %ju != "
> +	    "x %ju * y %ju", __func__, (uintmax_t)res, (uintmax_t)z,
> +	    (uintmax_t)rem, (uintmax_t)x, (uintmax_t)y));
> +	KASSERT(rem < z, ("%s: rem %ju >= z %ju\n", __func__,
> +	    (uintmax_t)rem, (uintmax_t)z);
> +
> +	return (res);
> +}
> +
>   static inline uint64_t
>   mul_u64_u32_shr(uint64_t x, uint32_t y, unsigned int shift)
>   {