From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from gate.crashing.org (gate.crashing.org [63.228.1.57]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (Client did not present a certificate) by ozlabs.org (Postfix) with ESMTPS id 2FA34B6F85 for ; Mon, 28 Mar 2011 10:25:30 +1100 (EST) Subject: Re: Early kernel debugging From: Benjamin Herrenschmidt To: Philipp Ittershagen In-Reply-To: <4D8F7B55.2050806@gate-nine.de> References: <201103250950.20423.dargaud@lpsc.in2p3.fr> <4D8F7B55.2050806@gate-nine.de> Content-Type: text/plain; charset="UTF-8" Date: Mon, 28 Mar 2011 10:25:16 +1100 Message-ID: <1301268316.2402.489.camel@pasglop> Mime-Version: 1.0 Cc: linuxppc-dev@lists.ozlabs.org, Guillaume Dargaud List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Sun, 2011-03-27 at 20:00 +0200, Philipp Ittershagen wrote: > On 03/25/2011 09:50 AM, Guillaume Dargaud wrote: > > Hello all, > > what can you do when the kernel you try to run stops before printing anything on the console ? > > http://elinux.org/Kernel_Debugging_Tips#Debugging_early_boot_problems > > Basically it means connecting a debugger to the running kernel (using > XMD, for example) and then reading the printk log buffer, which contains > the last lines printed. It actually mostly depends on the platform. There's various powerpc specific early debug mechanisms that are more/less robust/functional depending on the CPU type, the platform, etc... Look in udbg.c, there's a list of early debug hacks in there controlled by various config options. Cheers, Ben.