[Qemu-devel] [PATCH 2/5] gdbstub: gdb pass-through qemu monitor support

[Jason Wessel <jason.wessel@windriver.com>]

This patch adds a feature to the gdbstub to allow gdb to issue monitor
commands that can pass-through to the qemu monitor.

In order to make this work, the MAX_MON (the maximum number of monitor
connections) had to get incremented by 1 to support the case when the
gdbstub is setup along with all the other connections.  A small check
was added avoid strange crashes when you allocate too many qemu
monitor connections.

The monitor_handle_command had to be exported in order to allow
gdbstub to pass the strings directly to the monitor.  The gdbstub
registers as an output device of the qemu monitor such that no further
changes were needed to the monitor other than to have a global
variable in the gdbstub that controls when to transmit data from a
pass through monitor command to an attached debugger.

The qemu docs were updated to reflect this change.

Signed-off-by: Jason Wessel <jason.wessel@windriver.com>
---
 console.h     |    1 +
 gdbstub.c     |   47 +++++++++++++++++++++++++++++++++++++++++++----
 monitor.c     |    8 ++++++--
 qemu-doc.texi |   11 +++++++++++
 4 files changed, 61 insertions(+), 6 deletions(-)

diff --git a/console.h b/console.h
index c7f29f5..041b4ef 100644
--- a/console.h
+++ b/console.h
@@ -159,6 +159,7 @@ extern uint8_t _translate_keycode(const int key);
    does not need to include console.h  */
 /* monitor.c */
 void monitor_init(CharDriverState *hd, int show_banner);
+void monitor_handle_command(const char *cmdline);
 void term_puts(const char *str);
 void term_vprintf(const char *fmt, va_list ap);
 void term_printf(const char *fmt, ...) __attribute__ ((__format__ (__printf__, 1, 2)));
diff --git a/gdbstub.c b/gdbstub.c
index 4bc7999..833cdd9 100644
--- a/gdbstub.c
+++ b/gdbstub.c
@@ -33,6 +33,7 @@
 #include "qemu-char.h"
 #include "sysemu.h"
 #include "gdbstub.h"
+#include "console.h"
 #endif
 
 #include "qemu_socket.h"
@@ -70,6 +71,8 @@ typedef struct GDBState {
     int running_state;
 #else
     CharDriverState *chr;
+    CharDriverState *mon;
+    int allow_monitor;
 #endif
 } GDBState;
 
@@ -239,10 +242,11 @@ static int put_packet(GDBState *s, char *buf)
     return 0;
 }
 
-static void monitor_output(GDBState *s, const char *msg)
+static void monitor_output_len(GDBState *s, const char *msg, int len)
 {
     char *buf;
-    int len = strlen(msg);
+    if (!len)
+        len = strlen(msg);
 
     buf = malloc(len * 2 + 2);
     buf[0] = 'O';
@@ -251,6 +255,11 @@ static void monitor_output(GDBState *s, const char *msg)
     free(buf);
 }
 
+static void monitor_output(GDBState *s, const char *msg)
+{
+    monitor_output_len(s, msg, 0);
+}
+
 static void monitor_help(GDBState *s)
 {
     monitor_output(s, "gdbstub specific monitor commands:\n");
@@ -258,6 +267,7 @@ static void monitor_help(GDBState *s)
     monitor_output(s, "set s_step <0|1> -- Single Stepping enabled\n");
     monitor_output(s, "set s_irq <0|1> --  Single Stepping with qemu irq handlers enabled\n");
     monitor_output(s, "set s_timer <0|1> -- Single Stepping with qemu timers enabled\n");
+    monitor_output(s, "qemu monitor pass-through commands:\n");
 }
 
 #if defined(TARGET_I386)
@@ -994,8 +1004,14 @@ static void gdb_rcmd(GDBState *s, const char *p, char *buf, char *mem_buf)
         sstep_flags &= ~SSTEP_NOTIMER;
     } else if (!strcmp(mem_buf, "s_timer 0")) {
         sstep_flags |= SSTEP_NOTIMER;
-    } else if (!strcmp(mem_buf, "help") || !strcmp(mem_buf, "?")) {
-        monitor_help(s);
+    } else {
+        if (!strcmp(mem_buf, "help") || !strcmp(mem_buf, "?"))
+            monitor_help(s);
+#ifndef CONFIG_USER_ONLY
+        s->allow_monitor = 1;
+        monitor_handle_command(mem_buf);
+        s->allow_monitor = 0;
+#endif
     }
     put_packet(s, "OK");
 }
@@ -1536,6 +1552,26 @@ static void gdb_chr_event(void *opaque, int event)
     }
 }
 
+static int gdb_mon_chr_write(CharDriverState *chr, const uint8_t *buf, int len)
+{
+    GDBState *s = chr->opaque;
+    if (s->allow_monitor)
+        monitor_output_len(s, buf, len);
+    return len;
+}
+
+static CharDriverState *qemu_chr_open_gdb_mon(GDBState *s)
+{
+    CharDriverState *chr;
+
+    chr = qemu_mallocz(sizeof(CharDriverState));
+    if (!chr)
+        return NULL;
+    chr->chr_write = gdb_mon_chr_write;
+    chr->opaque = s;
+    return chr;
+}
+
 int gdbserver_start(const char *port)
 {
     GDBState *s;
@@ -1568,6 +1604,9 @@ int gdbserver_start(const char *port)
     qemu_chr_add_handlers(chr, gdb_chr_can_receive, gdb_chr_receive,
                           gdb_chr_event, s);
     qemu_add_vm_stop_handler(gdb_vm_stopped, s);
+    /* Initialize a monitor port for gdb */
+    s->mon = qemu_chr_open_gdb_mon(s);
+    monitor_init(s->mon, 0);
     return 0;
 }
 #endif
diff --git a/monitor.c b/monitor.c
index 236b827..2d2a110 100644
--- a/monitor.c
+++ b/monitor.c
@@ -69,7 +69,7 @@ typedef struct term_cmd_t {
     const char *help;
 } term_cmd_t;
 
-#define MAX_MON 4
+#define MAX_MON 5
 static CharDriverState *monitor_hd[MAX_MON];
 static int hide_banner;
 
@@ -2096,7 +2096,7 @@ static int default_fmt_size = 4;
 
 #define MAX_ARGS 16
 
-static void monitor_handle_command(const char *cmdline)
+void monitor_handle_command(const char *cmdline)
 {
     const char *p, *pstart, *typestr;
     char *q;
@@ -2649,6 +2649,10 @@ void monitor_init(CharDriverState *hd, int show_banner)
             break;
         }
     }
+    if (i >= MAX_MON) {
+        fprintf(stderr, "ERROR too many monitor connections requested\n");
+        exit(0);
+    }
 
     hide_banner = !show_banner;
 
diff --git a/qemu-doc.texi b/qemu-doc.texi
index 11c7058..f981b08 100644
--- a/qemu-doc.texi
+++ b/qemu-doc.texi
@@ -1976,6 +1976,17 @@ Turn off or on the the irq processing when single stepping, which is defaulted t
 Turn off or on the the timer processing when single stepping, which is defaulted to off.
 @end table
 
+You may also use gdb to send pass-through monitor commands to the qemu monitor.  It is easiest to start off with using just using @code{monitor help} to display the list of commands in available from the monitor.  Then you can prefix the @code{monitor} key word prior to any command.  The example below show the use of the qemu monitor's @code{info pci} command.
+
+@example
+(gdb) monitor info pci
+  Bus  0, device   0, function 0:
+    Host bridge: PCI device 1057:4801
+  Bus  0, device   1, function 0:
+    VGA controller: PCI device 1234:1111
+      BAR0: 32 bit memory at 0xf0000000 [0xf07fffff].
+@end example
+
 @node pcsys_os_specific
 @section Target OS specific information
 
-- 
1.5.5.1