[Qemu-devel] [RESEND][PATCH] gdbstub: Add vCont support

[Jan Kiszka <jan.kiszka@siemens.com>]

In order to set the VCPU for the next single-step command, you need gdb
6.8 or better - and this patch. It enhances the existing support for
representing VCPUs as threads to the gdb frontend by introducing the
vCont remote gdb command. This is used by gdb to switch the debugging
focus for single-stepping multi-threaded targets.


There was quite some discussion around this patch in the past, dealing
with the model for presenting VCPU as threads to the gdb front-end. This
patch should be merged nevertheless because

- this patch does not introduce the threading model, it only introduces
  vCont according to the exiting model used by qemu 0.10.x.

- current gdb provides no alternative yet, but we already have lots of
  use cases that are covered by the basic threading model.

- enhancing qemu later on with a true multicore model once gdb supports
  it will not obsolete this patch.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
---

 gdbstub.c |   58 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 files changed, 58 insertions(+), 0 deletions(-)

diff --git a/gdbstub.c b/gdbstub.c
index 8876c1d..1191dc2 100644
--- a/gdbstub.c
+++ b/gdbstub.c
@@ -1570,6 +1570,64 @@ static int gdb_handle_packet(GDBState *s, const char *line_buf)
             s->signal = 0;
         gdb_continue(s);
         return RS_IDLE;
+    case 'v':
+        if (strncmp(p, "Cont", 4) == 0) {
+            int res_signal, res_thread;
+
+            p += 4;
+            if (*p == '?') {
+                put_packet(s, "vCont;c;C;s;S");
+                break;
+            }
+            res = 0;
+            res_signal = 0;
+            res_thread = 0;
+            while (*p) {
+                int action, signal;
+
+                if (*p++ != ';') {
+                    res = 0;
+                    break;
+                }
+                action = *p++;
+                signal = 0;
+                if (action == 'C' || action == 'S')
+                    signal = strtoul(p, (char **)&p, 16);
+                else if (action != 'c' && action != 's') {
+                    res = 0;
+                    break;
+                }
+                thread = 0;
+                if (*p == ':')
+                    thread = strtoull(p+1, (char **)&p, 16);
+
+                action = tolower(action);
+                if (res == 0 || (res == 'c' && action == 's')) {
+                    res = action;
+                    res_signal = signal;
+                    res_thread = thread;
+                }
+            }
+            if (res) {
+                if (res_thread != -1 && res_thread != 0) {
+                    for (env = first_cpu; env != NULL; env = env->next_cpu)
+                        if (env->cpu_index + 1 == res_thread)
+                            break;
+                    if (env == NULL) {
+                        put_packet(s, "E22");
+                        break;
+                    }
+                    s->c_cpu = env;
+                }
+                if (res == 's')
+                    cpu_single_step(s->c_cpu, sstep_flags);
+                s->signal = res_signal;
+                gdb_continue(s);
+                return RS_IDLE;
+            }
+            break;
+        } else
+            goto unknown_command;
     case 'k':
         /* Kill the target */
         fprintf(stderr, "\nQEMU: Terminated via GDBstub\n");