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

[Alex Bennée]

Claudio Imbrenda <address@hidden> writes:

> 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);
> +        }
> +    }
> +}

I missed this last time but as gdb_single_step_cpus() is only called for
system emulation it breaks the linux-user compilation with:

  error: ‘gdb_single_step_cpus’ defined but not used [-Werror=unused-function]

> +
> +/*
> + * 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 {


--
Alex Bennée