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[PULL,28/31] gdbstub.c: fix GDB connection segfault caused by empty machines

Message ID 8c171da885807f7b534bdcde6757cd35b2969816.1485250702.git.mjt@msgid.tls.msk.ru
State New
Headers show

Commit Message

Michael Tokarev Jan. 24, 2017, 9:39 a.m. UTC 
From: Ziyue Yang <yzylivezh@hotmail.com>

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.

Signed-off-by: Ziyue Yang <skiver.cloud.yzy@gmail.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>
---
 gdbstub.c | 7 +++++++
 1 file changed, 7 insertions(+)
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Patch

diff --git a/gdbstub.c b/gdbstub.c
index de9b62b..27e0923 100644
--- a/gdbstub.c
+++ b/gdbstub.c
@@ -18,6 +18,7 @@ 
  */
 #include "qemu/osdep.h"
 #include "qapi/error.h"
+#include "qemu/error-report.h"
 #include "qemu/cutils.h"
 #include "cpu.h"
 #ifdef CONFIG_USER_ONLY
@@ -1732,6 +1733,12 @@  int gdbserver_start(const char *device)
     CharDriverState *mon_chr;
     ChardevCommon common = { 0 };
 
+    if (!first_cpu) {
+        error_report("gdbstub: meaningless to attach gdb to a "
+                     "machine without any CPU.");
+        return -1;
+    }
+
     if (!device)
         return -1;
     if (strcmp(device, "none") != 0) {