linux-kernel - Re: [PATCH v6 13/17] arm64:ilp32: add sys_ilp32.c and a separate table (in entry.S) to use it

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Date:	Fri, 13 Nov 2015 07:38:49 -0800
From:	Andrew Pinski <pinskia@...il.com>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	Andreas Schwab <schwab@...e.de>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Yury Norov <ynorov@...iumnetworks.com>,
	"Kapoor, Prasun" <Prasun.Kapoor@...iumnetworks.com>,
	Catalin Marinas <catalin.marinas@....com>,
	Nathan Lynch <Nathan_Lynch@...tor.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Alexander Graf <agraf@...e.de>,
	Alexey Klimov <klimov.linux@...il.com>, broonie@...nel.org,
	Jan Dakinevich <jan.dakinevich@...il.com>,
	Andrew Pinski <apinski@...ium.com>,
	David Daney <ddaney.cavm@...il.com>,
	bamvor.zhangjian@...wei.com,
	Philipp Tomsich <philipp.tomsich@...obroma-systems.com>,
	Andrey Konovalov <andrey.konovalov@...aro.org>,
	christoph.muellner@...obroma-systems.com
Subject: Re: [PATCH v6 13/17] arm64:ilp32: add sys_ilp32.c and a separate
 table (in entry.S) to use it

On Fri, Nov 13, 2015 at 7:34 AM, Arnd Bergmann <arnd@...db.de> wrote:
> On Thursday 12 November 2015 14:47:18 Andreas Schwab wrote:
>> Arnd Bergmann <arnd@...db.de> writes:
>>
>> > On Thursday 12 November 2015 10:44:55 Andreas Schwab wrote:
>> >> Arnd Bergmann <arnd@...db.de> writes:
>> >>
>> >> > What do you mean with 32-bit off_t?
>> >>
>> >> An ABI with 32-bit off_t, ie. all currently implemented 32-bit ABIs.
>> >>
>> >> > Do you mean that glibc emulates a 32-bit off_t on top of the 64-bit
>> >> > __kernel_loff_t?
>> >>
>> >> Glibc is bridging the user-space ABI to the kernel ABI.
>> >
>> > Ok, but why?
>>
>> That's how the ABI is defined right now.  I didn't make that up.
>
> Ok, I guess it will remain a mystery then.

The biggest question is here is how much compatibility do we want with
other 32bit ABIs?
Do we want off_t to be 32bit or 64bit?

>
> Should we perhaps define __ARCH_WANT_SYSCALL_OFF_T for the unistd.h
> file then, so we provide both the off_t and the loff_t based syscalls?

I think that is backwards ...

>
> That would avoid the extra wrapper in glibc when using a 32-bit
> off_t if that is the preferred mode for user space.


Other targets like tilegx does not do that and has a pure 32bit mode.
Only score does that.

Thanks,
Andrew

>
>         Arnd
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