[Qemu-devel] Re: [RESEND][PATCH] gdbstub: listen on ipv4 address

[Jan Kiszka]

Daniel P. Berrange wrote:
> On Wed, Jan 28, 2009 at 10:14:22AM +0100, Jan Kiszka wrote:
>> Anthony Liguori wrote:
>>> Sebastian Herbszt wrote:
>>>> Anthony Liguori wrote:
>>>>> Sebastian Herbszt wrote:
>>>>>> Make gdbstub listen on ipv4 address like before r5697.
>>>>> Any reason to make it explicit?
>>>> There seems to be no support for IPv6 in gdb.
>>> Are you unable to connect without the ipv4 option?  My understanding was
>>> that we shouldn't explicitly need this option.
>> inet_listen (which is finally called for this) falls back to PF_UNSPEC
>> when no protocol is given. I'm not sure if we can expect (according to
>> specs) that all our host OSes pick the protocol we want (normally IPv4).
> 
> There are three scenarios you need to consider wrt command line
> args for TCP
> 
>  - IP address - the parser determines whether it IPv4 or V6 
>    address and asets PF_INET / PF_INET6 as needed
> 
>  - Hostname - with PF_UNSPEC, and AI_ADDRCONFIG, getaddrinfo()
>    will resolve the name, and return zero or more IP addresses.
>    An IPv6 address is only returned if a NIC has IPv6 enabled.
>    An IPv4 address is only returned if a NIC has IPv4 enabled.
>    QEMU listens on the first address it gets
> 
>    If an IPv6 address is returned, QEMU *disables* IPV6_V6ONLY
>    socket option, so the kernel  also accepts IPv4 connections
>    on the IPv6 socket.
> 
>  - No hostname - with PF_UNSPEC, and AI_ADDRCONFIG, getaddrinf()
>    will return the 0.0.0.0 or :: depending on whether the host
>    has IPv6 enabled on any NICs. Again QEMU disables IPV6_V6ONLY
>    to ensure IPv4 connections can be accepted over the IPv6 socket
> 
> Finally the ipv4/v6 command line flags in QEMU can override
> the normal getaddrinfo() config. 
> 
> The GDB stub current code should be hitting scenario 3, and thus QEMU
> should be listening on both IPv4 and IPv6 ports.

That's true. gdb stumbled over optimizations and showed me the state
before the getaddrinf call. In fact, AF_INET6 is passed to socket() as
IPv6 is enabled for my host.

> 
> If everything is working as I describe above, we should not need any 
> special case to force disable IPv6 for GDB stub, even if GDB itself is
> IPv4 only - we always listen on IPv4 address even if we're also listening
> on IPv6, unless the command line explicitly has the ',ipv6' flag provided.
> 
> If this isn't working, then perhaps our call to disable the IPV6_V6ONLY 
> socket option is not working correctly on some OS ?

Independent of that, having a canonical command line switch for the
gdbstub has some value of its own. The current -s/-p duo is unfortunate.
Find a proposal below. Quick-tested only, breaks user mode (which is
hard-coded to IPv4, BTW).

Jan

--------->

diff --git a/gdbstub.c b/gdbstub.c
index c99c080..58e55f5 100644
--- a/gdbstub.c
+++ b/gdbstub.c
@@ -2411,26 +2411,20 @@ static void gdb_chr_event(void *opaque, int event)
     }
 }
 
-int gdbserver_start(const char *port)
+int gdbserver_start(const char *device)
 {
     GDBState *s;
-    char gdbstub_port_name[128];
-    int port_num;
-    char *p;
+    char gdbstub_device_name[128];
     CharDriverState *chr;
 
-    if (!port || !*port)
+    if (!device)
       return -1;
 
-    port_num = strtol(port, &p, 10);
-    if (*p == 0) {
-        /* A numeric value is interpreted as a port number.  */
-        snprintf(gdbstub_port_name, sizeof(gdbstub_port_name),
-                 "tcp::%d,nowait,nodelay,server", port_num);
-        port = gdbstub_port_name;
-    }
+    /* enforce required attributes */
+    snprintf(gdbstub_device_name, sizeof(gdbstub_device_name),
+             "%s,nowait,nodelay,server", device);
 
-    chr = qemu_chr_open("gdb", port, NULL);
+    chr = qemu_chr_open("gdb", gdbstub_device_name, NULL);
     if (!chr)
         return -1;
 
diff --git a/vl.c b/vl.c
index 3676537..a2424ed 100644
--- a/vl.c
+++ b/vl.c
@@ -3985,8 +3985,7 @@ static void help(int exitcode)
            "-monitor dev    redirect the monitor to char device 'dev'\n"
            "-pidfile file   write PID to 'file'\n"
            "-S              freeze CPU at startup (use 'c' to start 
execution)\n"
-           "-s              wait gdb connection to port\n"
-           "-p port         set gdb connection port [default=%s]\n"
+           "-s [dev]        wait for gdb connection on 'dev' 
[default=tcp::%s]\n"
            "-d item1,...    output log to %s (use -d ? for a list of log 
items)\n"
            "-hdachs c,h,s[,t]\n"
            "                force hard disk 0 physical geometry and the 
optional BIOS\n"
@@ -4050,6 +4049,7 @@ static void help(int exitcode)
 }
 
 #define HAS_ARG 0x0001
+#define OPT_ARG 0x0002
 
 enum {
     /* Please keep in synch with help, qemu_options[] and
@@ -4121,7 +4121,6 @@ enum {
     QEMU_OPTION_pidfile,
     QEMU_OPTION_S,
     QEMU_OPTION_s,
-    QEMU_OPTION_p,
     QEMU_OPTION_d,
     QEMU_OPTION_hdachs,
     QEMU_OPTION_L,
@@ -4239,8 +4238,7 @@ static const QEMUOption qemu_options[] = {
     { "monitor", HAS_ARG, QEMU_OPTION_monitor },
     { "pidfile", HAS_ARG, QEMU_OPTION_pidfile },
     { "S", 0, QEMU_OPTION_S },
-    { "s", 0, QEMU_OPTION_s },
-    { "p", HAS_ARG, QEMU_OPTION_p },
+    { "s", OPT_ARG, QEMU_OPTION_s },
     { "d", HAS_ARG, QEMU_OPTION_d },
     { "hdachs", HAS_ARG, QEMU_OPTION_hdachs },
     { "L", HAS_ARG, QEMU_OPTION_L },
@@ -4548,8 +4546,8 @@ static void termsig_setup(void)
 int main(int argc, char **argv, char **envp)
 {
 #ifdef CONFIG_GDBSTUB
-    int use_gdbstub;
-    const char *gdbstub_port;
+    int use_gdbstub = 0;
+    const char *gdbstub_dev = "tcp::" DEFAULT_GDBSTUB_PORT;
 #endif
     uint32_t boot_devices_bitmap = 0;
     int i;
@@ -4625,10 +4623,6 @@ int main(int argc, char **argv, char **envp)
     initrd_filename = NULL;
     ram_size = 0;
     vga_ram_size = VGA_RAM_SIZE;
-#ifdef CONFIG_GDBSTUB
-    use_gdbstub = 0;
-    gdbstub_port = DEFAULT_GDBSTUB_PORT;
-#endif
     snapshot = 0;
     nographic = 0;
     curses = 0;
@@ -4698,6 +4692,9 @@ int main(int argc, char **argv, char **envp)
                     exit(1);
                 }
                 optarg = argv[optind++];
+            } else if ((popt->flags & OPT_ARG) && optind < argc &&
+                       argv[optind][0] != '-') {
+                optarg = argv[optind++];
             } else {
                 optarg = NULL;
             }
@@ -4963,9 +4960,8 @@ int main(int argc, char **argv, char **envp)
 #ifdef CONFIG_GDBSTUB
             case QEMU_OPTION_s:
                 use_gdbstub = 1;
-                break;
-            case QEMU_OPTION_p:
-                gdbstub_port = optarg;
+                if (optarg)
+                    gdbstub_dev = optarg;
                 break;
 #endif
             case QEMU_OPTION_L:
@@ -5660,9 +5656,9 @@ int main(int argc, char **argv, char **envp)
     if (use_gdbstub) {
         /* XXX: use standard host:port notation and modify options
            accordingly. */
-        if (gdbserver_start(gdbstub_port) < 0) {
-            fprintf(stderr, "qemu: could not open gdbstub device on port 
'%s'\n",
-                    gdbstub_port);
+        if (gdbserver_start(gdbstub_dev) < 0) {
+            fprintf(stderr, "qemu: could not open gdbstub device on '%s'\n",
+                    gdbstub_dev);
             exit(1);
         }
     }

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