linux-kernel - Re: [PATCH] maple_tree: fix tracepoint string pointers

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Message-ID: <aQSOAkBbFkBfYxPs@akranes.kaiser.cx>
Date: Fri, 31 Oct 2025 11:22:58 +0100
From: Martin Kaiser <martin@...ser.cx>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: "Liam R . Howlett" <Liam.Howlett@...cle.com>,
	maple-tree@...ts.infradead.org, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] maple_tree: fix tracepoint string pointers

Thus wrote Andrew Morton (akpm@...ux-foundation.org):

> > -	trace_ma_op(__func__, mas);
> > +	trace_ma_op(TP_FCT, mas);

> What could cause the storage for __func__ to disappear as you suggest?

I see your point. For __func__, the compiler generates a local symbol in
.rodata that should always be accessible by its address.

One case that doesn't work without my patch would be trace-cmd record to save
the binary ringbuffer and trace-cmd report to parse it in userspace. The
address of __func__ can't be dereferenced from userspace but tracepoint_string
will add an entry to /sys/kernel/tracing/printk_formats

Best regards,
Martin