linux-kernel - Re: [RFC PATCH v2 3/8] tools/nolibc: i386: Implement syscall with 6 arguments

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Message-ID: <20220323071001.GA14186@1wt.eu>
Date:   Wed, 23 Mar 2022 08:10:01 +0100
From:   Willy Tarreau <w@....eu>
To:     Ammar Faizi <ammarfaizi2@...weeb.org>
Cc:     David Laight <David.Laight@...LAB.COM>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Alviro Iskandar Setiawan <alviro.iskandar@...weeb.org>,
        Nugraha <richiisei@...il.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        GNU/Weeb Mailing List <gwml@...r.gnuweeb.org>,
        "x86@...nel.org" <x86@...nel.org>,
        "llvm@...ts.linux.dev" <llvm@...ts.linux.dev>
Subject: Re: [RFC PATCH v2 3/8] tools/nolibc: i386: Implement syscall with 6
 arguments

On Wed, Mar 23, 2022 at 01:29:39PM +0700, Ammar Faizi wrote:
> On 3/22/22 8:37 PM, David Laight wrote:
> > dunno, 'asm' register variables are rather more horrid and
> > should probably only be used (for asm statements) when there aren't
> > suitable register constraints.
> > 
> > (I'm sure there is a comment about that in the gcc docs.)
> 
> ^ Hey David, yes you're right, that is very interesting...
> 
> I hit a GCC bug when playing with syscall6() implementation here.
> 
> Using register variables for all inputs for syscall6() causing GCC 11.2
> stuck in an endless loop with 100% CPU usage. Reproducible with several
> versions of GCC.
> 
> In GCC 6.3, the syscall6() implementation above yields ICE (Internal
> Compiler Error):
> ```
>   <source>: In function '__sys_mmap':
>   <source>:35:1: error: unable to find a register to spill

Now I'm pretty sure that it was the issue I faced when trying long ago,
I remember this error message before I found it wiser to give up.

Willy