linux-kernel - Re: [RFC Patch 6/9] Use virtual debug registers in process/thread handling code

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Message-ID: <20081007174852.GE4130@in.ibm.com>
Date:	Tue, 7 Oct 2008 23:18:52 +0530
From:	"K.Prasad" <prasad@...ux.vnet.ibm.com>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	linux-kernel@...r.kernel.org, Roland McGrath <roland@...hat.com>,
	akpm@...ux-foundation.org, mingo@...e.hu,
	jason.wessel@...driver.com, avi@...ranet.com,
	richardj_moore@...ibm.com
Subject: Re: [RFC Patch 6/9] Use virtual debug registers in process/thread
	handling code

On Tue, Oct 07, 2008 at 11:40:46AM -0400, Alan Stern wrote:
> On Tue, 7 Oct 2008, K.Prasad wrote:
> 
> > This patch enables the use of abstract/virtual debug registers in
> > process-handling routines.
> 
> ...
> > --- linux-bkpt-lkml-27-rc9.orig/arch/x86/kernel/process_32.c
> > +++ linux-bkpt-lkml-27-rc9/arch/x86/kernel/process_32.c
> > @@ -56,6 +56,8 @@
> >  #include <asm/cpu.h>
> >  #include <asm/kdebug.h>
> >  #include <asm/idle.h>
> > +#include <asm/debugreg.h>
> > +#include <asm/hw_breakpoint.h>
> >  
> >  asmlinkage void ret_from_fork(void) __asm__("ret_from_fork");
> >  
> > @@ -158,9 +160,11 @@ void cpu_idle(void)
> >  void __show_registers(struct pt_regs *regs, int all)
> >  {
> >  	unsigned long cr0 = 0L, cr2 = 0L, cr3 = 0L, cr4 = 0L;
> > -	unsigned long d0, d1, d2, d3, d6, d7;
> > +	unsigned long u_debugreg[8];
> >  	unsigned long sp;
> >  	unsigned short ss, gs;
> > +	struct thread_hw_breakpoint *thbi = current->thread.hw_breakpoint_info;
> > +	int i;
> >  
> >  	if (user_mode_vm(regs)) {
> >  		sp = regs->sp;
> > @@ -201,17 +205,18 @@ void __show_registers(struct pt_regs *re
> >  	printk("CR0: %08lx CR2: %08lx CR3: %08lx CR4: %08lx\n",
> >  			cr0, cr2, cr3, cr4);
> >  
> > -	get_debugreg(d0, 0);
> > -	get_debugreg(d1, 1);
> > -	get_debugreg(d2, 2);
> > -	get_debugreg(d3, 3);
> > +	if (thbi) {
> > +		for (i = 0; i < HB_NUM; ++i)
> > +			u_debugreg[i] = thbi->vdr_bps[i].info.address;
> > +		u_debugreg[7] = thbi->vdr7;
> > +	}
> > +	u_debugreg[6] = current->thread.vdr6;
> > +
> >  	printk("DR0: %08lx DR1: %08lx DR2: %08lx DR3: %08lx\n",
> > -			d0, d1, d2, d3);
> > +					u_debugreg[0], u_debugreg[1],
> > +						u_debugreg[2], u_debugreg[3]);
> >  
> > -	get_debugreg(d6, 6);
> > -	get_debugreg(d7, 7);
> > -	printk("DR6: %08lx DR7: %08lx\n",
> > -			d6, d7);
> > +	printk("DR6: %08lx DR7: %08lx\n", u_debugreg[6], u_debugreg[7]);
> 
> I don't like this at all.  show_registers() should display the physical
> register contents, not the virtualized values.  Ditto for the 64-byte
> version of this routine.
> 
> Alan Stern
> 
Agreed, will modify this!

Thanks,
K.Prasad

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