[Qemu-devel] [PATCH v2 2/2] gdbstub: Fix vCont behaviour

[Claudio Imbrenda]

When GDB issues a "vCont", QEMU was not handling it correctly when
multiple VCPUs are active.
For vCont, for each thread (VCPU), it can be specified whether to
single step, continue or stop that thread. The default is to stop a
thread.
However, when (for example) "vCont;s:2" is issued, all VCPUs continue
to run, although all but VCPU nr 2 are to be stopped.

This patch:
* adds some additional helper functions to selectively restart only
  some CPUs
* completely rewrites the vCont parsing code

Please note that this improvement only works in system emulation mode,
when in userspace emulation mode the old behaviour is preserved.

Signed-off-by: Claudio Imbrenda <address@hidden>
---
 gdbstub.c | 226 +++++++++++++++++++++++++++++++++++++++++++++++++-------------
 1 file changed, 179 insertions(+), 47 deletions(-)

diff --git a/gdbstub.c b/gdbstub.c
index ecea8c4..ea42afa 100644
--- a/gdbstub.c
+++ b/gdbstub.c
@@ -386,6 +386,61 @@ static inline void gdb_continue(GDBState *s)
 #endif
 }
 
+static void gdb_single_step_cpus(CPUState **scpus, int flags)
+{
+    CPUState *cpu;
+    int cx;
+
+    if (!scpus) {
+        CPU_FOREACH(cpu) {
+            cpu_single_step(cpu, flags);
+        }
+    } else {
+        for (cx = 0; scpus[cx]; cx++) {
+            cpu_single_step(scpus[cx], flags);
+        }
+    }
+}
+
+/*
+ * Resume execution, per CPU actions. For user-more emulation it's
+ * equivalent to gdb_continue .
+ */
+static int gdb_continue_partial(GDBState *s, char def, CPUState **scpus,
+                                                            CPUState **ccpus)
+{
+    int res = 0;
+#ifdef CONFIG_USER_ONLY
+    s->running_state = 1;
+#else
+    if (!runstate_needs_reset()) {
+        if (vm_prepare_start()) {
+            return 0;
+        }
+
+        if (def == 0) {
+            gdb_single_step_cpus(scpus, sstep_flags);
+            /* CPUs not in scpus or ccpus stay stopped */
+            qemu_clock_enable(QEMU_CLOCK_VIRTUAL, true);
+            resume_some_vcpus(scpus);
+            resume_some_vcpus(ccpus);
+        } else if (def == 'c' || def == 'C') {
+            gdb_single_step_cpus(scpus, sstep_flags);
+            qemu_clock_enable(QEMU_CLOCK_VIRTUAL, true);
+            resume_all_vcpus();
+        } else if (def == 's' || def == 'S') {
+            gdb_single_step_cpus(NULL, sstep_flags);
+            gdb_single_step_cpus(ccpus, 0);
+            qemu_clock_enable(QEMU_CLOCK_VIRTUAL, true);
+            resume_all_vcpus();
+        } else {
+            res = -1;
+        }
+    }
+#endif
+    return res;
+}
+
 static void put_buffer(GDBState *s, const uint8_t *buf, int len)
 {
 #ifdef CONFIG_USER_ONLY
@@ -784,6 +839,123 @@ static int is_query_packet(const char *p, const char 
*query, char separator)
         (p[query_len] == '\0' || p[query_len] == separator);
 }
 
+/**
+ * gdb_handle_vcont - Parses and handles a vCont packet.
+ * returns -1 if a command is unsupported, -22 if there is a format error,
+ *         0 on success.
+ */
+static int gdb_handle_vcont(GDBState *s, const char *p)
+{
+    CPUState **s_cpus, **c_cpus;
+    CPUState *curcpu;
+    int res, idx, signal, scnt, ccnt;
+    char cur_action, default_action, broadcast_action;
+    unsigned long tmp;
+
+    /*
+     * For us: vCont[;action[:thread-id]]...
+     * where action can be one of c s C<sig> S<sig>
+     */
+    for (idx = scnt = 0; p[idx]; idx++) {
+        if (p[idx] == ';') {
+            scnt++;
+        }
+    }
+    s_cpus = g_new(CPUState *, scnt + 1);
+    c_cpus = g_new(CPUState *, scnt + 1);
+    scnt = ccnt = signal = 0;
+    default_action = broadcast_action = 0;
+
+    /*
+     * res keeps track of what error we are returning, with -1 meaning
+     * that the command is unknown or unsupported, and thus returning
+     * an empty packet, while -22 returns an E22 packet due to
+     * invalid or incorrect parameters passed.
+     */
+    res = 0;
+    while (*p) {
+        if (*p != ';') {
+            res = -1;
+            break;
+        }
+        p++; /* skip the ; */
+
+        /* unknown/invalid/unsupported command */
+        if (*p != 'C' && *p != 'S' && *p != 'c' && *p != 's') {
+            res = -1;
+            break;
+        }
+        cur_action = *p;
+        if (*p == 'C' || *p == 'S') {
+            if (qemu_strtoul(p + 1, &p, 16, &tmp)) {
+                res = -22;
+                break;
+            }
+            signal = gdb_signal_to_target(tmp);
+        } else {
+            p++;
+        }
+        /* thread specified. special values: -1 = all, 0 = any */
+        if (*p == ':') {
+            /*
+             * cannot specify an action for a single thread when an action
+             * was already specified for all threads
+             */
+            if (broadcast_action) {
+                res = -22;
+                break;
+            }
+            p++;
+            if ((p[0] == '-') && (p[1] == '1')) {
+                /*
+                 * specifying an action for all threads when some threads
+                 * already have actions.
+                 */
+                if (scnt || ccnt) {
+                    res = -22;
+                    break;
+                }
+                broadcast_action = cur_action;
+                p += 2;
+                continue;
+            }
+            if (qemu_strtoul(p, &p, 16, &tmp)) {
+                res = -22;
+                break;
+            }
+            /* 0 means any thread, so we pick the first */
+            idx = tmp ? tmp : 1;
+            curcpu = find_cpu(idx);
+            if (!curcpu) {
+                res = -22;
+                break;
+            }
+            if (cur_action == 's' || cur_action == 'S') {
+                s_cpus[scnt++] = curcpu;
+            } else {
+                c_cpus[ccnt++] = curcpu;
+            }
+        } else { /* no thread specified */
+            if (default_action != 0) {
+                res = -22; /* error, can't specify multiple defaults! */
+                break;
+            }
+            default_action = cur_action;
+        }
+    }
+    if (!res) {
+        s->signal = signal;
+        s_cpus[scnt] = c_cpus[ccnt] = NULL;
+        default_action = broadcast_action ? broadcast_action : default_action;
+        gdb_continue_partial(s, default_action, s_cpus, c_cpus);
+    }
+
+    g_free(s_cpus);
+    g_free(c_cpus);
+
+    return res;
+}
+
 static int gdb_handle_packet(GDBState *s, const char *line_buf)
 {
     CPUState *cpu;
@@ -829,60 +1001,20 @@ static int gdb_handle_packet(GDBState *s, const char 
*line_buf)
         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 = gdb_signal_to_target(strtoul(p, (char **)&p, 16));
-                    if (signal == -1) {
-                        signal = 0;
-                    }
-                } 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;
-                }
-            }
+
+            res = gdb_handle_vcont(s, p);
+
             if (res) {
-                if (res_thread != -1 && res_thread != 0) {
-                    cpu = find_cpu(res_thread);
-                    if (cpu == NULL) {
-                        put_packet(s, "E22");
-                        break;
-                    }
-                    s->c_cpu = cpu;
-                }
-                if (res == 's') {
-                    cpu_single_step(s->c_cpu, sstep_flags);
+                if (res == -22) {
+                    put_packet(s, "E22");
+                    break;
                 }
-                s->signal = res_signal;
-                gdb_continue(s);
-                return RS_IDLE;
+                goto unknown_command;
             }
             break;
         } else {
-- 
1.9.1