[Qemu-devel] [PATCH v8 2/2] gdbstub: Fix vCont behaviour

[Claudio Imbrenda <imbrenda@linux.vnet.ibm.com>]

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 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 <imbrenda@linux.vnet.ibm.com>
---
 gdbstub.c | 209 ++++++++++++++++++++++++++++++++++++++++++++++++--------------
 1 file changed, 162 insertions(+), 47 deletions(-)

diff --git a/gdbstub.c b/gdbstub.c
index de9b62b..0068f0e 100644
--- a/gdbstub.c
+++ b/gdbstub.c
@@ -386,6 +386,60 @@ static inline void gdb_continue(GDBState *s)
 #endif
 }
 
+/*
+ * Resume execution, per CPU actions. For user-mode emulation it's
+ * equivalent to gdb_continue.
+ */
+static int gdb_continue_partial(GDBState *s, char *newstates)
+{
+    CPUState *cpu;
+    int res = 0;
+#ifdef CONFIG_USER_ONLY
+    /*
+     * This is not exactly accurate, but it's an improvement compared to the
+     * previous situation, where only one CPU would be single-stepped.
+     */
+    CPU_FOREACH(cpu) {
+        if (newstates[cpu->cpu_index] == 's') {
+            cpu_single_step(cpu, sstep_flags);
+        }
+    }
+    s->running_state = 1;
+#else
+    int flag = 0;
+
+    if (!runstate_needs_reset()) {
+        if (vm_prepare_start()) {
+            return 0;
+        }
+
+        CPU_FOREACH(cpu) {
+            switch (newstates[cpu->cpu_index]) {
+            case 0:
+            case 1:
+                break; /* nothing to do here */
+            case 's':
+                cpu_single_step(cpu, sstep_flags);
+                cpu_resume(cpu);
+                flag = 1;
+                break;
+            case 'c':
+                cpu_resume(cpu);
+                flag = 1;
+                break;
+            default:
+                res = -1;
+                break;
+            }
+        }
+    }
+    if (flag) {
+        qemu_clock_enable(QEMU_CLOCK_VIRTUAL, true);
+    }
+#endif
+    return res;
+}
+
 static void put_buffer(GDBState *s, const uint8_t *buf, int len)
 {
 #ifdef CONFIG_USER_ONLY
@@ -784,6 +838,107 @@ 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 -ENOTSUP if a command is unsupported, -EINVAL or -ERANGE if there is
+ *         a format error, 0 on success.
+ */
+static int gdb_handle_vcont(GDBState *s, const char *p)
+{
+    int res, idx, signal = 0;
+    char cur_action;
+    char *newstates;
+    unsigned long tmp;
+    CPUState *cpu;
+#ifdef CONFIG_USER_ONLY
+    int max_cpus = 1; /* global variable max_cpus exists only in system mode */
+
+    CPU_FOREACH(cpu) {
+        max_cpus = max_cpus <= cpu->cpu_index ? cpu->cpu_index + 1 : max_cpus;
+    }
+#endif
+    /* uninitialised CPUs stay 0 */
+    newstates = g_new0(char, max_cpus);
+
+    /* mark valid CPUs with 1 */
+    CPU_FOREACH(cpu) {
+        newstates[cpu->cpu_index] = 1;
+    }
+
+    /*
+     * res keeps track of what error we are returning, with -ENOTSUP meaning
+     * that the command is unknown or unsupported, thus returning an empty
+     * packet, while -EINVAL and -ERANGE cause an E22 packet, due to invalid,
+     *  or incorrect parameters passed.
+     */
+    res = 0;
+    while (*p) {
+        if (*p++ != ';') {
+            res = -ENOTSUP;
+            goto out;
+        }
+
+        cur_action = *p++;
+        if (cur_action == 'C' || cur_action == 'S') {
+            cur_action = tolower(cur_action);
+            res = qemu_strtoul(p + 1, &p, 16, &tmp);
+            if (res) {
+                goto out;
+            }
+            signal = gdb_signal_to_target(tmp);
+        } else if (cur_action != 'c' && cur_action != 's') {
+            /* unknown/invalid/unsupported command */
+            res = -ENOTSUP;
+            goto out;
+        }
+        /* thread specification. special values: (none), -1 = all; 0 = any */
+        if ((p[0] == ':' && p[1] == '-' && p[2] == '1') || (p[0] != ':')) {
+            if (*p == ':') {
+                p += 3;
+            }
+            for (idx = 0; idx < max_cpus; idx++) {
+                if (newstates[idx] == 1) {
+                    newstates[idx] = cur_action;
+                }
+            }
+        } else if (*p == ':') {
+            p++;
+            res = qemu_strtoul(p, &p, 16, &tmp);
+            if (res) {
+                goto out;
+            }
+            idx = tmp;
+            /* 0 means any thread, so we pick the first valid CPU */
+            if (!idx) {
+                idx = cpu_index(first_cpu);
+            }
+
+            /*
+             * If we are in user mode, the thread specified is actually a
+             * thread id, and not an index. We need to find the actual
+             * CPU first, and only then we can use its index.
+             */
+            cpu = find_cpu(idx);
+            /* invalid CPU/thread specified */
+            if (!idx || !cpu) {
+                res = -EINVAL;
+                goto out;
+            }
+            /* only use if no previous match occourred */
+            if (newstates[cpu->cpu_index] == 1) {
+                newstates[cpu->cpu_index] = cur_action;
+            }
+        }
+    }
+    s->signal = signal;
+    gdb_continue_partial(s, newstates);
+
+out:
+    g_free(newstates);
+
+    return res;
+}
+
 static int gdb_handle_packet(GDBState *s, const char *line_buf)
 {
     CPUState *cpu;
@@ -829,60 +984,20 @@ 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 == -EINVAL) || (res == -ERANGE)) {
+                    put_packet(s, "E22");
+                    break;
                 }
-                s->signal = res_signal;
-                gdb_continue(s);
-                return RS_IDLE;
+                goto unknown_command;
             }
             break;
         } else {
-- 
2.7.4