linux-kernel - Re: [PATCH 1/2] powerpc: Move the single step enable code to a generic path

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Message-ID: <50B3B092.90605@linutronix.de>
Date:	Mon, 26 Nov 2012 19:10:26 +0100
From:	Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:	"Suzuki K. Poulose" <suzuki@...ibm.com>
CC:	oleg@...hat.com, ananth@...ibm.com, srikar@...ux.vnet.ibm.com,
	peterz@...radead.org, benh@...nel.crashing.org, mingo@...e.hu,
	anton@...hat.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] powerpc: Move the single step enable code to a generic
 path

On 11/26/2012 12:05 PM, Suzuki K. Poulose wrote:
> diff --git a/arch/powerpc/include/asm/probes.h b/arch/powerpc/include/asm/probes.h
> index 5f1e15b..836e9b9 100644
> --- a/arch/powerpc/include/asm/probes.h
> +++ b/arch/powerpc/include/asm/probes.h
> @@ -38,5 +38,34 @@ typedef u32 ppc_opcode_t;
>   #define is_trap(instr)		(IS_TW(instr) || IS_TWI(instr))
>   #endif /* CONFIG_PPC64 */
>
> +#ifdef CONFIG_PPC_ADV_DEBUG_REGS
> +#define MSR_SINGLESTEP	(MSR_DE)
> +#else
> +#define MSR_SINGLESTEP	(MSR_SE)
> +#endif
> +
> +/* Enable single stepping for the current task */
> +static inline void enable_single_step(struct pt_regs *regs)
> +{
> +
> +	/*
> +	 * We turn off async exceptions to ensure that the single step will
> +	 * be for the instruction we have the kprobe on, if we dont its
it is

> +	 * possible we'd get the single step reported for an exception handler
> +	 * like Decrementer or External Interrupt
> +	 */

Hmmm. The TRM for E400 says

|5.11.1 e500 Exception Priorities
|The following is a prioritized listing of e500 exceptions:
|   4. Critical input
|   5. Debug interrupt
|   6. External input
|   22. Decrementer

The list has been cut down a little. That means the debug interrupt
comes before external interrupt and before the decrement fires.

And if single step is what wakes you up then DBSR[ICMP] is set. Am I
missing something or is this FSL only not not book-e

>   #endif /* __KERNEL__ */
>   #endif	/* _ASM_POWERPC_PROBES_H */

Sebastian
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