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

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Message-ID: <20240911144412.GA16954@redhat.com>
Date: Wed, 11 Sep 2024 16:44:13 +0200
From: Oleg Nesterov <oleg@...hat.com>
To: Roman Kisel <romank@...ux.microsoft.com>
Cc: akpm@...ux-foundation.org, apais@...rosoft.com, benhill@...rosoft.com,
	ebiederm@...ssion.com, linux-kernel@...r.kernel.org,
	ssengar@...rosoft.com, sunilmut@...rosoft.com,
	torvalds@...ux-foundation.org, vdso@...bites.dev,
	workingjubilee@...il.com
Subject: Re: [PATCH 1/1] ptrace: Get tracer PID without reliance on the proc
 FS

We certainly can't understand each other. At least, I certainly can't.

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?

Once again, what I tried to suggest is a single "nop" function,
"void please_insert_the_breakpoint_here()" which simply does asm("ret") and

	#define breakpoint_if_debugging()	\
		please_insert_the_breakpoint_here()

Or, to make it more cheap,

	#define breakpoint_if_debugging()	\
		asm volatile ("call please_insert_the_breakpoint_here" : ASM_CALL_CONSTRAINT);

so that compiler will know that breakpoint_if_debugging() doesn't change the regs.

Again, again, I am not saying that this is necessarily the best solution.
Just I fail to understand your email, sorry.

Oleg.