Re: [Qemu-devel] [Qemu-arm] [PATCH v5 03/16] gdbstub: add multiprocess support to '?' packets

[Luc Michel <luc.michel@greensocs.com>]

Hi Edgar,

On 11/13/18 12:06 PM, Edgar E. Iglesias wrote:
> On Sat, Nov 10, 2018 at 09:11:34AM +0100, Luc Michel wrote:
>> The gdb_get_cpu_pid() function does the PID lookup for the given CPU. It
>> checks if the CPU is a direct child of a CPU cluster. If it is, the
>> returned PID is the cluster ID plus one (cluster IDs start at 0, GDB
>> PIDs at 1). When the CPU is not a child of such a container, the PID of
>> the first process is returned.
>>
>> The gdb_fmt_thread_id() function generates the string to be used to identify
>> a given thread, in a response packet for the peer. This function
>> supports generating thread IDs when multiprocess mode is enabled (in the
>> form `p<pid>.<tid>').
>>
>> Use them in the reply to a '?' request.
>>
>> Signed-off-by: Luc Michel <luc.michel@greensocs.com>
>> Acked-by: Alistair Francis <alistair.francis@wdc.com>
> 
> 
> This is also theoretical but:
> When looking at this, it seems like you could have lazily created
> the s->processes array entries (if you find a cluster but the
> no valid entry in s->processes). Then we could perhaps eliminate the
> scan of all objects at startup and also support CPU/Cluster hotplug.
Yes you are right, this could be an improvement to this series to add
cluster hotplug support (CPU hotplug is actually supported). It's a
little bit tricky though since we would have to maintain the
s->processes array and properly signal to GDB when a process dies.

Cheers,
Luc

> 
> Anyway, this looks good to me!
> Reviewed-by: Edgar E. Iglesias <edgar.iglesias@xilinx.com>
> 
> Cheers,
> Edgar
> 
> 
>> ---
>>  gdbstub.c | 60 +++++++++++++++++++++++++++++++++++++++++++++++++++++--
>>  1 file changed, 58 insertions(+), 2 deletions(-)
>>
>> diff --git a/gdbstub.c b/gdbstub.c
>> index 0d70b89598..d26bad4b67 100644
>> --- a/gdbstub.c
>> +++ b/gdbstub.c
>> @@ -638,10 +638,52 @@ static int memtox(char *buf, const char *mem, int len)
>>          }
>>      }
>>      return p - buf;
>>  }
>>  
>> +static uint32_t gdb_get_cpu_pid(const GDBState *s, CPUState *cpu)
>> +{
>> +#ifndef CONFIG_USER_ONLY
>> +    gchar *path, *name;
>> +    Object *obj;
>> +    CPUClusterState *cluster;
>> +    uint32_t ret;
>> +
>> +    path = object_get_canonical_path(OBJECT(cpu));
>> +    name = object_get_canonical_path_component(OBJECT(cpu));
>> +
>> +    if (path == NULL) {
>> +        ret = s->processes[0].pid;
>> +        goto out;
>> +    }
>> +
>> +    /*
>> +     * Retrieve the CPU parent path by removing the last '/' and the CPU name
>> +     * from the CPU canonical path. */
>> +    path[strlen(path) - strlen(name) - 1] = '\0';
>> +
>> +    obj = object_resolve_path_type(path, TYPE_CPU_CLUSTER, NULL);
>> +
>> +    if (obj == NULL) {
>> +        ret = s->processes[0].pid;
>> +        goto out;
>> +    }
>> +
>> +    cluster = CPU_CLUSTER(obj);
>> +    ret = cluster->cluster_id + 1;
>> +
>> +out:
>> +    g_free(name);
>> +    g_free(path);
>> +
>> +    return ret;
>> +
>> +#else
>> +    return s->processes[0].pid;
>> +#endif
>> +}
>> +
>>  static const char *get_feature_xml(const char *p, const char **newp,
>>                                     CPUClass *cc)
>>  {
>>      size_t len;
>>      int i;
>> @@ -907,10 +949,23 @@ static CPUState *find_cpu(uint32_t thread_id)
>>      }
>>  
>>      return NULL;
>>  }
>>  
>> +static char *gdb_fmt_thread_id(const GDBState *s, CPUState *cpu,
>> +                           char *buf, size_t buf_size)
>> +{
>> +    if (s->multiprocess) {
>> +        snprintf(buf, buf_size, "p%02x.%02x",
>> +                 gdb_get_cpu_pid(s, cpu), cpu_gdb_index(cpu));
>> +    } else {
>> +        snprintf(buf, buf_size, "%02x", cpu_gdb_index(cpu));
>> +    }
>> +
>> +    return buf;
>> +}
>> +
>>  static int is_query_packet(const char *p, const char *query, char separator)
>>  {
>>      unsigned int query_len = strlen(query);
>>  
>>      return strncmp(p, query, query_len) == 0 &&
>> @@ -1018,22 +1073,23 @@ static int gdb_handle_packet(GDBState *s, const char *line_buf)
>>      const char *p;
>>      uint32_t thread;
>>      int ch, reg_size, type, res;
>>      uint8_t mem_buf[MAX_PACKET_LENGTH];
>>      char buf[sizeof(mem_buf) + 1 /* trailing NUL */];
>> +    char thread_id[16];
>>      uint8_t *registers;
>>      target_ulong addr, len;
>>  
>>      trace_gdbstub_io_command(line_buf);
>>  
>>      p = line_buf;
>>      ch = *p++;
>>      switch(ch) {
>>      case '?':
>>          /* TODO: Make this return the correct value for user-mode.  */
>> -        snprintf(buf, sizeof(buf), "T%02xthread:%02x;", GDB_SIGNAL_TRAP,
>> -                 cpu_gdb_index(s->c_cpu));
>> +        snprintf(buf, sizeof(buf), "T%02xthread:%s;", GDB_SIGNAL_TRAP,
>> +                 gdb_fmt_thread_id(s, s->c_cpu, thread_id, sizeof(thread_id)));
>>          put_packet(s, buf);
>>          /* Remove all the breakpoints when this query is issued,
>>           * because gdb is doing and initial connect and the state
>>           * should be cleaned up.
>>           */
>> -- 
>> 2.19.1
>>
>>