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

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Date:	Tue, 7 Oct 2008 11:40:46 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	"K.Prasad" <prasad@...ux.vnet.ibm.com>
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, 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

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