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:	Thu, 12 Nov 2015 10:22 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	Andreas Schwab <schwab@...e.de>
Cc:	linux-arm-kernel@...ts.infradead.org,
	Yury Norov <ynorov@...iumnetworks.com>, pinskia@...il.com,
	Prasun.Kapoor@...iumnetworks.com, catalin.marinas@....com,
	Nathan_Lynch@...tor.com, linux-kernel@...r.kernel.org,
	agraf@...e.de, klimov.linux@...il.com,
	Andrew Pinski <Andrew.Pinski@...iumnetworks.com>,
	broonie@...nel.org, jan.dakinevich@...il.com,
	Andrew Pinski <apinski@...ium.com>, ddaney.cavm@...il.com,
	bamvor.zhangjian@...wei.com, philipp.tomsich@...obroma-systems.com,
	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 Thursday 12 November 2015 09:58:43 Andreas Schwab wrote:
> Arnd Bergmann <arnd@...db.de> writes:
> 
> > I think either way is fine for the two examples. I think it's clear
> > that we want __NR_llseek as 62 and __NR_mmap2 as 222. Whether those
> > use the compat_sys_llseek/compat_sys_mmap2_wrapper or
> > sys_lseek/sys_mmap entry points is not overly important, we can use
> > whatever is more convenient to glibc: if we can kill off an
> > architecture specific wrapper function in glibc by adding one line
> > to the kernel, that seems worthwhile.
> 
> Currently most off_t-like syscalls need a new glibc wrapper since the
> existing ones are either for 32bit off_t+off64_t (with split off64_t
> syscall arguments) or pure 64bit off_t architectures.  Since ilp32 now
> (mostly) has 32bit off_t, but 64bit off_t-like syscalls neither of them
> fit.

What do you mean with 32-bit off_t? Do you mean that glibc emulates
a 32-bit off_t on top of the 64-bit __kernel_loff_t? That sounds a bit
backwards. I would expect that all new architectures that only have
__kernel_loff_t based syscalls but not __kernel_off_t based ones only
ever use a 64-bit off_t in libc.

	Arnd
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