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

["Edgar E. Iglesias" <edgar.iglesias@xilinx.com>]

On Wed, Nov 14, 2018 at 09:43:27AM +0100, Luc Michel wrote:
> 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.

Hi Luc,

IMO, support for hotplugging could be added incrementally with follow-up work.
I wonder if the GDB stub would handle it today, without your patches?

Cheers,
Edgar


> 
> 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
> >>
> >>