linux-kernel - Re: futex(2) man page update help request

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Message-ID: <5374E2A4.2070408@zytor.com>
Date:	Thu, 15 May 2014 08:52:04 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	chrubis@...e.cz,
	"Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>
CC:	Darren Hart <dvhart@...ux.intel.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...e.hu>, Jakub Jelinek <jakub@...hat.com>,
	"linux-man@...r.kernel.org" <linux-man@...r.kernel.org>,
	lkml <linux-kernel@...r.kernel.org>,
	Davidlohr Bueso <davidlohr.bueso@...com>,
	Arnd Bergmann <arnd@...db.de>,
	Steven Rostedt <rostedt@...dmis.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Linux API <linux-api@...r.kernel.org>,
	"Carlos O'Donell" <carlos@...hat.com>
Subject: Re: futex(2) man page update help request

On 05/15/2014 08:42 AM, chrubis@...e.cz wrote:
> Hi!
>> People have a number of times noted that there are problems
>> with syscall(), but I'm not knowledgeable on the details.
>> I'd happily take a patch to the man page (which, for historical
>> reasons, is actually syscall(2)) that explains the the problems 
>> (and ideally notes those platforms where there are no problems).
> 
> Have a look at this commit that tries to deal with passing 64 bit
> numbers to syscalls. On 32 bit ABI (but not on X32) these needs to be
> split up (accordingly to machine endianity).
> 
> https://github.com/linux-test-project/ltp/commit/04afb02b4280a20c262054e8f99a3fad4ad54916
> 

That is wrong, too.  That assumes that there will never be padding
words, which isn't true in the general case, either.

I really believe the proper fix is to use assembly syscall stubs.  In
klibc I build a fairly elaborate machinery to autogenerate such syscall
stubs for a variety of architectures.

	-hpa

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