Re: [Patch 4/6] Modify process and processor handling code to recognise hardware debug registers

[David Gibson <dwg@au1.ibm.com>]

On Mon, May 25, 2009 at 06:46:50AM +0530, K.Prasad wrote:
> Modify process handling code to recognise hardware debug registers during copy
> and flush operations. Introduce a new TIF_DEBUG task flag to indicate a
> process's use of debug register. Load the debug register values into a
> new CPU during initialisation.

[snip]
> Index: linux-2.6-tip.hbkpt/arch/powerpc/kernel/process.c
> ===================================================================
> --- linux-2.6-tip.hbkpt.orig/arch/powerpc/kernel/process.c
> +++ linux-2.6-tip.hbkpt/arch/powerpc/kernel/process.c
> @@ -50,6 +50,7 @@
>  #include <asm/syscalls.h>
>  #ifdef CONFIG_PPC64
>  #include <asm/firmware.h>
> +#include <asm/hw_breakpoint.h>
>  #endif
>  #include <linux/kprobes.h>
>  #include <linux/kdebug.h>
> @@ -254,8 +255,10 @@ void do_dabr(struct pt_regs *regs, unsig
>  			11, SIGSEGV) == NOTIFY_STOP)
>  		return;
>  
> +#ifndef CONFIG_PPC64
>  	if (debugger_dabr_match(regs))
>  		return;
> +#endif
>  
>  	/* Clear the DAC and struct entries.  One shot trigger */
>  #if defined(CONFIG_BOOKE)
> @@ -372,8 +375,13 @@ struct task_struct *__switch_to(struct t
>  
>  #endif /* CONFIG_SMP */
>  
> +#ifdef CONFIG_PPC64
> +		if (unlikely(test_tsk_thread_flag(new, TIF_DEBUG)))
> +			arch_install_thread_hw_breakpoint(new);
> +#else
>  	if (unlikely(__get_cpu_var(current_dabr) != new->thread.dabr))
>  		set_dabr(new->thread.dabr);
> +#endif /* CONFIG_PPC64 */
>  
>  #if defined(CONFIG_BOOKE)
>  	/* If new thread DAC (HW breakpoint) is the same then leave it */
> @@ -550,6 +558,10 @@ void show_regs(struct pt_regs * regs)
>  void exit_thread(void)
>  {
>  	discard_lazy_cpu_state();
> +#ifdef CONFIG_PPC64
> +	if (unlikely(test_tsk_thread_flag(current, TIF_DEBUG)))
> +		flush_thread_hw_breakpoint(current);
> +#endif /* CONFIG_PPC64 */
>  }
>  
>  void flush_thread(void)
> @@ -605,6 +617,9 @@ int copy_thread(unsigned long clone_flag
>  	struct pt_regs *childregs, *kregs;
>  	extern void ret_from_fork(void);
>  	unsigned long sp = (unsigned long)task_stack_page(p) + THREAD_SIZE;
> +#ifdef CONFIG_PPC64
> +	struct task_struct *tsk = current;

I don't see any point to adding this variable, just reference current
directly  below.

> +#endif
>  
>  	CHECK_FULL_REGS(regs);
>  	/* Copy registers */
> @@ -672,6 +687,9 @@ int copy_thread(unsigned long clone_flag
>  	 * function.
>   	 */
>  	kregs->nip = *((unsigned long *)ret_from_fork);
> +
> +	if (unlikely(test_tsk_thread_flag(tsk, TIF_DEBUG)))
> +		copy_thread_hw_breakpoint(tsk, p, clone_flags);
>  #else
>  	kregs->nip = (unsigned long)ret_from_fork;
>  #endif

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson