linux-kernel - RE: printf internals

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Message-ID: <D83235F0F3C86D4D889D8B9A0DA8C6D7012AF56B@corpexc01.corp.networkrobots.com>
Date:	Wed, 19 Dec 2007 15:31:15 -0800
From:	"Siva Prasad" <sprasad@...io.net>
To:	"Scott Russell" <catfather@...poo.net>
Cc:	"Clemens Koller" <clemens.koller@...gramm.de>,
	"David Newall" <david@...idnewall.com>,
	<linux-kernel@...r.kernel.org>
Subject: RE: printf internals


Yes!... this is a embedded system, and will not have monitor. So, serial
is the default console.

I pass cmdline as "root=/dev/ram rw console=ttyS0,115200"

Thanks
Siva


-----Original Message-----
From: Scott Russell [mailto:catfather@...poo.net] 
Sent: Wednesday, December 19, 2007 3:31 PM
To: Siva Prasad
Cc: Clemens Koller; David Newall; linux-kernel@...r.kernel.org
Subject: RE: printf internals


On Wed, 2007-12-19 at 14:33 -0800, Siva Prasad wrote:
> Thank you very much for your response Clemens.
> 
> I tried strace on a regular system. It does not show which tty, etc.,
as it uses the stdout (fd = 1) and write(1, ...) to it.
> 
> This is not a student project. I am trying to build my own kernel and
ramdisk. Kernel boots fine to a point where it starts accessing ramdisk
and executes init scripts. From there on nothing gets printed. I did
some debugging and found that prints of user land programs are not
coming to the serial console, while kernel prints are working fine. I
found all the programs getting executed, by placing a printk in execve
routine and printing the arguments.
> 
> So, I wanted to trace down the path from user program to the kernel
and see why it is not printing messages from user program. I placed a
printk in drivers/char/tty_io.c:tty_write() and it is not getting called
from my file system. I tried the same thing on my good system (say
regular PC) and it works as expected.
> 
> Any clues that can help debug this issue is highly appreciated.
> How can I get access to the same printf string inside kernel.

This sounds like you're printing out the serial console instead.

-- 
Scott <catfather@...poo.net>
AIM: BlueCame1

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