linux-kernel - Re: [PATCH v5 5/8] powerpc/watchpoint: Fix exception handling for CONFIG_HAVE_HW

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Date:   Tue, 25 Aug 2020 14:06:21 +0200
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     Ravi Bangoria <ravi.bangoria@...ux.ibm.com>,
        christophe.leroy@....fr
Cc:     mpe@...erman.id.au, mikey@...ling.org, paulus@...ba.org,
        naveen.n.rao@...ux.vnet.ibm.com, pedromfc@...ux.ibm.com,
        rogealve@...ux.ibm.com, jniethe5@...il.com,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 5/8] powerpc/watchpoint: Fix exception handling for
 CONFIG_HAVE_HW_BREAKPOINT=N



Le 25/08/2020 à 13:07, Ravi Bangoria a écrit :
> Hi Christophe,
> 
>>> diff --git a/arch/powerpc/kernel/ptrace/ptrace-noadv.c 
>>> b/arch/powerpc/kernel/ptrace/ptrace-noadv.c
>>> index 57a0ab822334..866597b407bc 100644
>>> --- a/arch/powerpc/kernel/ptrace/ptrace-noadv.c
>>> +++ b/arch/powerpc/kernel/ptrace/ptrace-noadv.c
>>> @@ -286,11 +286,16 @@ long ppc_del_hwdebug(struct task_struct *child, 
>>> long data)
>>>       }
>>>       return ret;
>>>   #else /* CONFIG_HAVE_HW_BREAKPOINT */
>>> +    if (child->thread.hw_brk[data - 1].flags & HW_BRK_FLAG_DISABLED)
>>
>> I think child->thread.hw_brk[data - 1].flags & HW_BRK_FLAG_DISABLED 
>> should go around additionnal ()
> 
> Not sure I follow.

Neither do I ....

I thought that GCC would emit a warning for that, but in fact it only 
emit warnings for things like:

	if (flags & HW_BRK_FLAG_DISABLED == HW_BRK_FLAG_DISABLED)

> 
>>
>>> +        goto del;
>>> +
>>>       if (child->thread.hw_brk[data - 1].address == 0)
>>>           return -ENOENT;
>>
>> What about replacing the above if by:
>>      if (!(child->thread.hw_brk[data - 1].flags) & 
>> HW_BRK_FLAG_DISABLED) &&
>>          child->thread.hw_brk[data - 1].address == 0)
>>          return -ENOENT;
> okay.. that's more compact.
> 
> But more importantly, what I wanted to know is whether 
> CONFIG_HAVE_HW_BREAKPOINT
> is set or not in production/distro builds for 8xx. Because I see it's 
> not set in
> 8xx defconfigs.

Yes in our production configs with have CONFIG_PERF_EVENTS, that implies 
CONFIG_HAVE_HW_BREAKPOINT

Christophe