linux-kernel - Re: [PATCH] update fix X86_64 procfs provide stack information for threads

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Date:	Tue, 03 Nov 2009 10:06:24 +0100
From:	Stefani Seibold <stefani@...bold.net>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	linux-kernel <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Americo Wang <xiyou.wangcong@...il.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH] update fix X86_64 procfs provide stack information for
 threads

Am Dienstag, den 03.11.2009, 09:28 +0100 schrieb Ingo Molnar:
> > --- linux-2.6.32-rc5/arch/x86/include/asm/processor.h	2009-10-16 02:41:50.000000000 +0200
> > +++ linux-2.6.32-rc5.new/arch/x86/include/asm/processor.h	2009-11-02 10:39:47.177909657 +0100
> > @@ -1000,7 +1001,13 @@
> >  #define thread_saved_pc(t)	(*(unsigned long *)((t)->thread.sp - 8))
> >  
> >  #define task_pt_regs(tsk)	((struct pt_regs *)(tsk)->thread.sp0 - 1)
> > -#define KSTK_ESP(tsk)		-1 /* sorry. doesn't work for syscall. */
> > +
> > +#ifdef CONFIG_IA32_EMULATION
> > +extern unsigned long KSTK_ESP(struct task_struct *task);
> > +#else
> > +#define KSTK_ESP(task)		((task)->thread.usersp)
> > +#endif
> > +
> >  #endif /* CONFIG_X86_64 */
> >  
> >  extern void start_thread(struct pt_regs *regs, unsigned long new_ip,
> > --- linux-2.6.32-rc5/arch/x86/kernel/process_64.c	2009-10-16 02:41:50.000000000 +0200
> > +++ linux-2.6.32-rc5.new/arch/x86/kernel/process_64.c	2009-11-02 10:48:23.614936810 +0100
> > @@ -664,3 +669,11 @@
> >  	return do_arch_prctl(current, code, addr);
> >  }
> >  
> > +#ifdef CONFIG_IA32_EMULATION
> > +unsigned long KSTK_ESP(struct task_struct *task)
> > +{
> > +	return (test_tsk_thread_flag(task, TIF_IA32)) ? \
> > +			(task_pt_regs(task)->sp) : \
> > +			((task)->thread.usersp);
> > +}
> > +#endif
> 
> That's quite ugly. The KSTK_ESP() function should be unconditional and 
> the #ifdef should be eliminated. If CONFIG_IA32_EMULATION is turned off 
> (whichis rare) then TIF_IA32 wont be set so the function should work 
> fine.
> 
> Thanks,
> 
> 	Ingo

Hi Ingo,

come on, thats not fair. This would be not the only piece of ugly code
in the x86_64 implementation. It is much better than the previous hack
where KSTK_ESP always returns a wrong hard coded value. That is really
ugly!!!!

It took me 6 hours to analyze the x64_64 code, most of them written in
assembler. I think it is a first solution, which makes the procfs stack
information work on this architecture and that was the goal.

I will remove the #ifdef's and repost the patch. Please accept this
patch, which make the KSTP_ESP thing on x86_64 better as before.

I am not a x64_64 bit hacker, i have not the knowledge to make a perfect
solution for this architecture. Also i am not a full time kernel hacker,
i have customers who wait for their projects.

Greeting,
Stefani


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