Re: [PATCH 1/1] ptrace: Get tracer PID without reliance on the proc FS

[Roman Kisel <romank@linux.microsoft.com>]

On 9/11/2024 12:53 PM, Oleg Nesterov wrote:
> Roman,
> 
> I can only repeat that we can't understand each other. Quite possibly my bad.
> 

Oleg,

I'll re-read the whole thread to see where I can improve.
Didn't mean to cause the undue burden for you. My apologies, will make a
note to myself to be crisper and more concise at the very least.

> On 09/11, Roman Kisel wrote:
>>
>> On 09/11, Oleg Nesterov wrote:
>>
>>> On 09/10, Roman Kisel wrote:
>>>>
>>>> On 09/09, Oleg wrote:
>>>>
>>>
>>>>> Yet another thing in this discussion I can't understand... sorry, I tried.
>>>>> You do not need to teach, say, gdb to recognize this pattern. You can just do
>>>>>
>>>>> 	$ gdb -ex 'b please_insert_the_breakpoint_here' ...
>>>>>
>>>>> Nevermind, as I have already said you can safely ignore me. I still do not
>>>>> see any "real" use-case for breakpoint_if_debugging(), but I guess that is
>>>>> due to my ignorance and lack of imagination.
>>>>
>>>> I've started this so let me butt in and take up the gaunlet.
>>>>
>>>> Lambda's would be the most prominent example to me[1]. The toolchain
>>>> doesn't give them the user-accesible type and the name as it does for
>>>> the functions.
>>>
>>> And?
>>
>> You wanted an example of '"real" use-case for breakpoint_if_debugging()':
> 
> Then why does your email explain that c++ lambdas don't have a good name?
> Why doesi it mention lambdas at all?
> 

I was making the point that setting a breakpoint on the lambda is quite
laborious, and instead one can put "breakpoint_if_debugging()" inside
of it.

>>>>> Nevermind, as I have already said you can safely ignore me. I still do not
>>>>> see any "real" use-case for breakpoint_if_debugging(), but I guess that is
>>>>> due to my ignorance and lack of imagination.
>>
>> I have provided them, and illustrated how it is tiresome to set the breakpoint
>> in the debugger in these cases so can add a call to breakpoint_if_debugging()
>> to these places instead.
> 
> Instead of what??? Instead of
> 
> 	#define breakpoint_if_debugging()	\
> 		asm volatile ("call please_insert_the_breakpoint_here" : ASM_CALL_CONSTRAINT);
> 
> plus -ex 'b please_insert_the_breakpoint_here'???
> 
> If you say that this is ugly I won't even argue. But instead of what?
> 
> Roman, I am leaving this thread, sorry. But let me try to summarize.
> Your patch was buggy and you seem to agree. Feel free to send V2 and I will
> be happy to review it correctness-wise. But:
> 
> 	- please keep Eric/Linus cc'ed
> 
> 	- please try to make your changelog more convincing. And in particular,
> 	  please explain why !!current->ptrace is not enough and this feature
> 	  needs the tracer's pid.
> 
> 	  If possible, please provide a clear/simple/artificial/whatever example
> 	  of the (pseudo)code which can justify this feature.

Oleg,

I owe you a great deal of gratitude for giving my arguments a chance! I
won't reply more to this thread, too. Will use the relevant points
from the list you kindly provided where that applies when posting
to LKML in the future.

> Oleg.

-- 
Thank you,
Roman