linux-kernel - Re: [PATCH v13 8/9] Add 32 bit VDSO time support for 32 bit kernel

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Date:	Sat, 8 Feb 2014 23:21:23 -0800
From:	Andi Kleen <ak@...ux.intel.com>
To:	stefani@...bold.net
Cc:	gregkh@...uxfoundation.org, linux-kernel@...r.kernel.org,
	x86@...nel.org, tglx@...utronix.de, mingo@...hat.com,
	hpa@...or.com, aarcange@...hat.com, john.stultz@...aro.org,
	luto@...capital.net, xemul@...allels.com, gorcunov@...nvz.org,
	andriy.shevchenko@...ux.intel.com, Martin.Runge@...de-schwarz.com,
	Andreas.Brief@...de-schwarz.com
Subject: Re: [PATCH v13 8/9] Add 32 bit VDSO time support for 32 bit kernel

On Sat, Feb 08, 2014 at 09:22:30PM -0800, Andi Kleen wrote:
> > +notrace static long vdso_fallback_gettime(long clock, struct timespec *ts)
> > +{
> > +	long ret;
> > +
> > +	asm(
> > +		"push %%ebx \n"
> > +		"mov %2,%%ebx \n"
> > +		"call VDSO32_vsyscall \n"
> > +		"pop %%ebx \n"
> > +		: "=a" (ret)
> > +		: "0" (__NR_clock_gettime), "d" (clock), "c" (ts)
> > +		: "memory");
> 
> The push/mov/pop could be just replaced with "b"?

Actually thinking about it more you likely did that to avoid errors
with -fPIC right? In this case you still need to supply correct dwarf2
unwind annotations.

Also this change is still needed:

> Also I if this calls syscall.S:__kernel_vsyscall it clobbers more registers
> (ecx at least?) and you need to describe that to gcc with a + 
> 
> Same in the other sys calls.
> 
> > @@ -310,6 +311,11 @@ int arch_setup_additional_pages(struct linux_binprm *bprm, int uses_interp)
> >  	unsigned long addr;
> >  	int ret = 0;
> >  	bool compat;
> > +	struct vm_area_struct *vma;
> > +	extern char __vvar_page;
> > +#ifdef CONFIG_HPET_TIMER
> > +	extern unsigned long hpet_address;
> > +#endif
> 
> Put this into a header.
> 
> > +++ b/arch/x86/vdso/vdso32/vclock_gettime.c
> > @@ -0,0 +1,16 @@
> > +#define BUILD_VDSO32
> > +
> > +#ifdef CONFIG_X86_64
> > +
> > +#define _ASM_X86_PAGE_H
> > +
> > +#define __pa(x)                0
> > +#define __va(x)                0
> > +
> > +#undef CONFIG_ILLEGAL_POINTER_VALUE
> > +#define CONFIG_ILLEGAL_POINTER_VALUE   0
> 
> This needs some comments.
> 
> Why are the __pa/__va defines safe?
> 
> The rest of the patchkit looks reasonable to me from a quick read.
> Much better than the first version.
> 
> -Andi
> 
> -- 
> ak@...ux.intel.com -- Speaking for myself only

-- 
ak@...ux.intel.com -- Speaking for myself only
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