From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:53647) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1cTerA-0004Cg-MF for qemu-devel@nongnu.org; Tue, 17 Jan 2017 20:16:09 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1cTer9-000224-OK for qemu-devel@nongnu.org; Tue, 17 Jan 2017 20:16:08 -0500 MIME-Version: 1.0 In-Reply-To: References: <1484666391-15089-1-git-send-email-skiver.cloud.yzy@gmail.com> From: Yang Ziyue Date: Wed, 18 Jan 2017 09:16:06 +0800 Message-ID: Content-Type: text/plain; charset=UTF-8 Subject: Re: [Qemu-devel] [PATCH] gdbstub.c: fix GDB connection segfault caused by empty machines List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Thomas Huth Cc: qemu-devel@nongnu.org, qemu-trivial@nongnu.org, Paolo Bonzini , Anthony Liguori , Ziyue Yang 2017-01-18 1:27 GMT+08:00 Thomas Huth : > > On 17.01.2017 16:19, Ziyue Yang wrote: > > From: Ziyue Yang > > > > This patch is to fix the segmentation fault caused by attaching > > GDB to a QEMU instance initialized with "-M none" option. > > > > The bug can be reproduced by > > > >> ./qemu-system-x86_64 -M none -nographic -S -s > > > > and attach a GDB to it by > > > >> gdb -ex 'target remote :1234 > > > > The segmentation fault was originally caused by trying to read > > the information about CPU when communicating with GDB. However, > > it's impossible for any control flow to exist on an empty machine, > > nor can CPU's be hot plugged to an empty machine later by QOM > > commands. So I think simply disabling GDB connections on empty > > machines makes sense. > > Yes, this sounds like a proper and easy fix for the problem. > > > Signed-off-by: Ziyue Yang > > --- > > gdbstub.c | 6 ++++++ > > 1 file changed, 6 insertions(+) > > > > diff --git a/gdbstub.c b/gdbstub.c > > index de62d26..413e817 100644 > > --- a/gdbstub.c > > +++ b/gdbstub.c > > @@ -1731,6 +1731,12 @@ int gdbserver_start(const char *device) > > CharDriverState *mon_chr; > > ChardevCommon common = { 0 }; > > > > + if (!first_cpu) { > > + fprintf(stderr, "gdbstub: meaningless to attach gdb to a " > > + "machine without any CPU.\n"); > > + return -1; > > + } > > Could you maybe rather use error_report() instead of fprintf()? I think > that's the preferred way to print out an error in QEMU nowadays. Sure. I've sent a v2 version patch fixing that. > > > Thomas >