Re: [patch v4 08/13] remote, btrace: add branch trace remote ops

Pedro Alves
2012-11-28T19:23:46Z

New packets always need documentation. And NEWS entries too.
The new "set remote XXX" commands need docs too.

On 11/27/2012 10:49 AM, markus.t.metzger@intel.com wrote:
> From: Markus Metzger <markus.t.metzger@intel.com>
>
> Add the gdb remote target operations for branch tracing. We define the following
> packets:
>
> qbtrace:<ptid> query if new trace data is available for a thread
> returns "yes" or "no" or "Enn"

The code isn't handling "no".

>
> Qbtrace:on:<ptid> enable branch tracing for one thread
> returns "OK" or "Enn"
>
> Qbtrace:off:<ptid> disable branch tracing for one thread
> returns "OK" or "Enn"

Nit, I'd put <ptid> first:

> Qbtrace:<ptid>:on enable branch tracing for one thread
> returns "OK" or "Enn"
>
> Qbtrace:<ptid>:off disable branch tracing for one thread
> returns "OK" or "Enn"

How does "btrace enable all" for new threads work with remote targets?
GDB isn't notified of new threads until they stop for some reason.

>
> qXfer:btrace:read:<ptid> read the full branch trace data for one thread

No need to pass the thread in the annex. qXfer packets use the general
context set by remote_xfer_partial -> set_current_thread.

> (_initialize_remote): Add btrace packets.

Say:

(_initialize_remote): Add packet configuration for
branch tracing.

> diff --git a/gdb/remote.c b/gdb/remote.c
> index 929d4f5..c512b93 100644
> --- a/gdb/remote.c
> +++ b/gdb/remote.c
> @@ -67,6 +67,7 @@
> #include "ax.h"
> #include "ax-gdb.h"
> #include "agent.h"
> +#include "btrace.h"

Should be mentioned on the change log too.

>
> /* Temp hacks for tracepoint encoding migration. */
> static char *target_buf;
> @@ -1292,6 +1293,9 @@ enum {
> PACKET_qXfer_fdpic,
> PACKET_QDisableRandomization,
> PACKET_QAgent,
> + PACKET_qbtrace,
> + PACKET_Qbtrace,
> + PACKET_qXfer_btrace,
> PACKET_MAX
> };
>
> @@ -3946,6 +3950,10 @@ static struct protocol_feature remote_protocol_features[] = {
> { "QAgent", PACKET_DISABLE, remote_supported_packet, PACKET_QAgent},
> { "tracenz", PACKET_DISABLE,
> remote_string_tracing_feature, -1 },
> + { "qbtrace", PACKET_DISABLE, remote_supported_packet, PACKET_qbtrace },
> + { "Qbtrace", PACKET_DISABLE, remote_supported_packet, PACKET_Qbtrace },
> + { "qXfer:btrace:read", PACKET_DISABLE, remote_supported_packet,
> + PACKET_qXfer_btrace }
> };
>
> static char *remote_support_xml;
> @@ -8682,6 +8690,10 @@ remote_xfer_partial (struct target_ops *ops, enum target_object object,
> return remote_read_qxfer (ops, "uib", annex, readbuf, offset, len,
> &remote_protocol_packets[PACKET_qXfer_uib]);
>
> + case TARGET_OBJECT_BTRACE:
> + return remote_read_qxfer (ops, "btrace", annex, readbuf, offset, len,
> + &remote_protocol_packets[PACKET_qXfer_btrace]);
> +
> default:
> return -1;
> }
> @@ -11001,6 +11013,137 @@ remote_can_use_agent (void)
> return (remote_protocol_packets[PACKET_QAgent].support != PACKET_DISABLE);
> }
>
> +struct btrace_target_info
> +{
> + /* The ptid of the traced thread. */
> + ptid_t ptid;
> +};

Hmm, why would you need to store this? To get at a struct btrace_target_info,
you need to start from a struct thread_info, so why not just pass that
down, or pass the ptid down?

> +
> +/* Check whether the target supports branch tracing. */
> +static int
> +remote_supports_btrace (void)
> +{
> + if (remote_protocol_packets[PACKET_qbtrace].support != PACKET_ENABLE)
> + return 0;
> + if (remote_protocol_packets[PACKET_Qbtrace].support != PACKET_ENABLE)
> + return 0;
> + if (remote_protocol_packets[PACKET_qXfer_btrace].support != PACKET_ENABLE)
> + return 0;
> +
> + return 1;
> +}
> +
> +/* Enable branch tracing for @ptid. */
> +static struct btrace_target_info *
> +remote_enable_btrace (ptid_t ptid)
> +{
> + struct packet_config *packet = &remote_protocol_packets[PACKET_Qbtrace];
> + struct remote_state *rs = get_remote_state ();
> + struct btrace_target_info *tinfo = NULL;
> + char *buf = rs->buf;
> + char *endbuf = rs->buf + get_remote_packet_size ();
> +
> + if (packet->support != PACKET_ENABLE)
> + error (_("Target does not support branch tracing."));
> +
> + buf += xsnprintf (buf, endbuf - buf, "%s", packet->name);
> + buf += xsnprintf (buf, endbuf - buf, ":on:");
> + buf = write_ptid (buf, endbuf, ptid);
> + putpkt (rs->buf);
> + getpkt (&rs->buf, &rs->buf_size, 0);
> +
> + if (packet_ok (rs->buf, packet) != PACKET_OK)
> + error (_("Could not enable branch tracing for %s."),
> + target_pid_to_str (ptid));
> +
> + tinfo = xzalloc (sizeof (*tinfo));
> + tinfo->ptid = ptid;
> +
> + return tinfo;
> +}
> +
> +/* Disable branch tracing. */
> +static void
> +remote_disable_btrace (struct btrace_target_info *tinfo)
> +{
> + struct packet_config *packet = &remote_protocol_packets[PACKET_Qbtrace];
> + struct remote_state *rs = get_remote_state ();
> + char *buf = rs->buf;
> + char *endbuf = rs->buf + get_remote_packet_size ();
> +
> + if (packet->support != PACKET_ENABLE)
> + error (_("Target does not support branch tracing."));
> +
> + buf += xsnprintf (buf, endbuf - buf, "%s", packet->name);
> + buf += xsnprintf (buf, endbuf - buf, ":off:");
> + buf = write_ptid (buf, endbuf, tinfo->ptid);
> + putpkt (rs->buf);
> + getpkt (&rs->buf, &rs->buf_size, 0);
> +
> + if (packet_ok (rs->buf, packet) != PACKET_OK)
> + error (_("Could not disable branch tracing for %s."),
> + target_pid_to_str (tinfo->ptid));
> +
> + xfree (tinfo);
> +}

remote_enable_btrace/remote_disable_btrace are almost identical.
You could factor this out to a function that takes a on/off boolean.

--
Pedro Alves