linux-kernel - Re: [PATCH 20/25] arm64:ilp32: add sys_ilp32.c and a separate table (in entry.S) to use it

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Date:	Mon, 25 Apr 2016 21:19:13 +0300
From:	Yury Norov <ynorov@...iumnetworks.com>
To:	Catalin Marinas <catalin.marinas@....com>
CC:	<arnd@...db.de>, <linux-arm-kernel@...ts.infradead.org>,
	<linux-kernel@...r.kernel.org>, <linux-arch@...r.kernel.org>,
	<linux-s390@...r.kernel.org>, <pinskia@...il.com>,
	<Prasun.Kapoor@...iumnetworks.com>, <schwab@...e.de>,
	<broonie@...nel.org>, <linux-doc@...r.kernel.org>,
	<heiko.carstens@...ibm.com>, <agraf@...e.de>,
	<klimov.linux@...il.com>,
	Andrew Pinski <Andrew.Pinski@...iumnetworks.com>,
	<bamvor.zhangjian@...wei.com>, Andrew Pinski <apinski@...ium.com>,
	<schwidefsky@...ibm.com>, <Nathan_Lynch@...tor.com>,
	<joseph@...esourcery.com>,
	<christoph.muellner@...obroma-systems.com>
Subject: Re: [PATCH 20/25] arm64:ilp32: add sys_ilp32.c and a separate table
 (in entry.S) to use it

On Mon, Apr 25, 2016 at 06:26:56PM +0100, Catalin Marinas wrote:
> On Wed, Apr 06, 2016 at 01:08:42AM +0300, Yury Norov wrote:
> > --- a/arch/arm64/kernel/entry.S
> > +++ b/arch/arm64/kernel/entry.S
> > @@ -715,9 +715,13 @@ ENDPROC(ret_from_fork)
> >   */
> >  	.align	6
> >  el0_svc:
> > -	adrp	stbl, sys_call_table		// load syscall table pointer
> >  	uxtw	scno, w8			// syscall number in w8
> >  	mov	sc_nr, #__NR_syscalls
> > +#ifdef CONFIG_ARM64_ILP32
> > +	ldr	x16, [tsk, #TI_FLAGS]
> > +	tbnz	x16, #TIF_32BIT_AARCH64, el0_ilp32_svc // We are using ILP32
> > +#endif
> 
> There is another ldr x16, [tsk, #TI_FLAGS] load further down in the
> el0_svc_naked block. We should rework these a bit to avoid loading the
> same location twice unnecessarily. E.g. move the ldr x16 just before
> el0_svc_naked and branch one line after in case of the ILP32 syscall.
> 

Yes, I thiks we can refactor it. Thanks for a catch.

> > +	adrp	stbl, sys_call_table		// load syscall table pointer
> >  el0_svc_naked:					// compat entry point
> >  	stp	x0, scno, [sp, #S_ORIG_X0]	// save the original x0 and syscall number
> >  	enable_dbg_and_irq
> > @@ -737,6 +741,12 @@ ni_sys:
> >  	b	ret_fast_syscall
> >  ENDPROC(el0_svc)
> >  
> > +#ifdef CONFIG_ARM64_ILP32
> > +el0_ilp32_svc:
> > +	adrp	stbl, sys_call_ilp32_table // load syscall table pointer
> > +	b el0_svc_naked
> > +#endif
> > +
> >  	/*
> >  	 * This is the really slow path.  We're going to be doing context
> >  	 * switches, and waiting for our parent to respond.
> 
> -- 
> Catalin