From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:38182) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1cTXXL-0002lU-5Q for qemu-devel@nongnu.org; Tue, 17 Jan 2017 12:27:12 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1cTXXH-000459-Vv for qemu-devel@nongnu.org; Tue, 17 Jan 2017 12:27:11 -0500 References: <1484666391-15089-1-git-send-email-skiver.cloud.yzy@gmail.com> From: Thomas Huth Message-ID: Date: Tue, 17 Jan 2017 18:27:04 +0100 MIME-Version: 1.0 In-Reply-To: <1484666391-15089-1-git-send-email-skiver.cloud.yzy@gmail.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit 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: Ziyue Yang , qemu-devel@nongnu.org, qemu-trivial@nongnu.org Cc: Paolo Bonzini , Anthony Liguori , Ziyue Yang 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. Thomas