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

From: "Edgar E. Iglesias" <edgar.iglesias@gmail.com>
To: Luc Michel <luc.michel@greensocs.com>
Cc: qemu-devel@nongnu.org, "Peter Maydell" <peter.maydell@linaro.org>,
	"Eduardo Habkost" <ehabkost@redhat.com>,
	alistair@alistair23.me, mark.burton@greensocs.com,
	"Philippe Mathieu-Daudé" <f4bug@amsat.org>,
	saipava@xilinx.com, edgari@xilinx.com, qemu-arm@nongnu.org
Subject: Re: [Qemu-devel] [Qemu-arm] [PATCH v5 03/16] gdbstub: add multiprocess support to '?' packets
Date: Tue, 13 Nov 2018 12:06:36 +0100	[thread overview]
Message-ID: <20181113110636.GH1148@toto> (raw)
In-Reply-To: <20181110081147.4027-4-luc.michel@greensocs.com>

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.

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
> 
> 