Linux-ARM-Kernel Archive on
 help / color / Atom feed
From: Mars Cheng <>
To: Steven Rostedt <>
Cc: Andress Kuo <>,
	CC Hwang <>,,,
Subject: Re: [PATCH 1/1] tracing: Fix event_trace_printk loss on printk_format.
Date: Wed, 13 Feb 2019 12:54:10 +0800
Message-ID: <1550033650.7648.2.camel@mtkswgap22> (raw)
In-Reply-To: <20190212204113.5ecaa2a1@gandalf.local.home>

Hi Steve

On Tue, 2019-02-12 at 20:41 -0500, Steven Rostedt wrote:
> On Tue, 12 Feb 2019 19:41:57 +0800
> Mars Cheng <> wrote:
> > From: Andress Kuo <>
> > 
> > If fmt on event_trace_printk is not a constant, It means that something not
> > guaranteed, so the compiler optimizes the fmt out, and then the
> > __trace_printk_fmt section is not filled. if __trace_printk_fmt is not
> > filled, the kernel will not allocate the special buffers needed for the
> > event_trace_printk() and then not shown in the file output
> > sys/kernel/debug/tracing/print_formats.
> > 
> > Adding a "__used" to the variable in the __trace_printk_fmt section on
> > event_trace_printk() will keep it around, even though it is set to NULL.
> > This will keep the string from being printed in the
> > sys/kernel/debug/tracing/printk_formats section.
> > 
> > We can also refer to commit 3debb0a9ddb1 ("tracing: Fix trace_printk()
> > to print when not using bprintk()")that it had similar issue on path of
> > trace_printk().
> Honestly, I don't even remember why that macro was created. I think
> it's a remnant from the creation of the trace events. I think the best
> solution is just to nuke it. It shouldn't be used anymore.
> I'll dig a bit deeper into the history of that macro, but I'm thinking
> it shouldn't exist anymore.
> [ /me returns from walking down memory lane ]
> Wow, that brings back some wild memories. Yes, that macro must die, and
> I wish the history of it could die along with it ;-) The horror of the
> old ways I tell you. The event_trace_printk() was the original way we
> displayed events! No real formatting, no parsing my userspace tools. It
> was just a glamorized printk. It was called TRACE_FORMAT() which was
> deprecated by today's TRACE_EVENT().
> That macro should have been removed by commit b8e65554d80b4.
> Please just send a patch to delete that macro. Let's not be maintaining
> it. It gives me nightmares.
> -- Steve

Got it, I will send another patch to remove the nightmares. :-)


linux-arm-kernel mailing list

  reply index

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-02-12 11:41 Mars Cheng
2019-02-13  1:41 ` Steven Rostedt
2019-02-13  4:54   ` Mars Cheng [this message]
2019-02-13  6:49     ` Mars Cheng
2019-02-13 13:45       ` Steven Rostedt

Reply instructions:

You may reply publically to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=1550033650.7648.2.camel@mtkswgap22 \ \ \ \ \ \ \ \

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

Linux-ARM-Kernel Archive on

Archives are clonable:
	git clone --mirror linux-arm-kernel/git/0.git
	git clone --mirror linux-arm-kernel/git/1.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 linux-arm-kernel linux-arm-kernel/ \
	public-inbox-index linux-arm-kernel

Example config snippet for mirrors

Newsgroup available over NNTP:

AGPL code for this site: git clone public-inbox