linux-kernel - Re: [PATCH 00/13] [RFC] Rust support

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Message-ID: <YHrvq6/d4iw8SLAc@hirez.programming.kicks-ass.net>
Date:   Sat, 17 Apr 2021 16:24:43 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Willy Tarreau <w@....eu>
Cc:     Matthew Wilcox <willy@...radead.org>,
        Miguel Ojeda <miguel.ojeda.sandonis@...il.com>,
        Wedson Almeida Filho <wedsonaf@...gle.com>,
        Miguel Ojeda <ojeda@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        rust-for-linux@...r.kernel.org,
        Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        Linux Doc Mailing List <linux-doc@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 00/13] [RFC] Rust support

On Sat, Apr 17, 2021 at 01:46:23PM +0200, Willy Tarreau wrote:
> For me the old trick of casting one side as long long still works:
> 
>   unsigned long long mul3264(unsigned int a, unsigned int b)
>   {
>         return (unsigned long long)a * b;
>   }
> 
> i386:
>   00000000 <mul3264>:
>      0: 8b 44 24 08           mov    0x8(%esp),%eax
>      4: f7 64 24 04           mull   0x4(%esp)
>      8: c3                    ret    
> 
> x86_64:
>   0000000000000000 <mul3264>:
>      0: 89 f8                 mov    %edi,%eax
>      2: 89 f7                 mov    %esi,%edi
>      4: 48 0f af c7           imul   %rdi,%rax
>      8: c3                    retq   
> 
> Or maybe you had something else in mind ?

Last time I tried it, the thing refused :/ which is how we ended up with
mul_u32_u32() in asm.