linux-kernel - Re: [RFC][PATCH] ftrace: Make DYNAMIC_FTRACE always enabled for architectures that support it

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Message-ID: <20250704111248.511cc248@gandalf.local.home>
Date: Fri, 4 Jul 2025 11:12:48 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: LKML <linux-kernel@...r.kernel.org>, Linux trace kernel
 <linux-trace-kernel@...r.kernel.org>, Masami Hiramatsu
 <mhiramat@...nel.org>, Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
 Mark Rutland <mark.rutland@....com>, Alexandre Ghiti <alex@...ti.fr>,
 ChenMiao <chenmiao.ku@...il.com>, linux-arch@...r.kernel.org
Subject: Re: [RFC][PATCH] ftrace: Make DYNAMIC_FTRACE always enabled for
 architectures that support it

On Thu, 3 Jul 2025 13:58:17 -0700
Linus Torvalds <torvalds@...ux-foundation.org> wrote:

> So the reason I dislike the HAVE_xyz pattern is exactly that there
> _isn't_ a pattern. When there are fifteen different patterns, it's not
> a pattern at all.
> 
> That said, maybe it's better to have one place that has that "if
> FUNCTION_TRACER, even if I despise the nonsensical "helper
> indirection" just because of the random naming.

At least with HAVE_FTRACE_* there is a pattern. The HAVE_* may not be
consistent across other parts of the kernel, but it has been with ftrace.

As I have stated, ftrace is very tightly coupled with the architectures due
to the assembly written trampolines. And having a simple way for the
architectures to denote what it supports and what it does not makes the
generic code much simpler to implement.

-- Steve