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From: Andrew Burgess <aburgess@redhat.com>
To: Thiago Jung Bauermann via Gdb-patches
	<gdb-patches@sourceware.org>,
	gdb-patches@sourceware.org
Cc: Thiago Jung Bauermann <thiago.bauermann@linaro.org>
Subject: Re: [PATCH v3 6/8] gdb/remote: Parse tdesc field in stop reply and threads list XML
Date: Wed, 01 Feb 2023 14:32:51 +0000	[thread overview]
Message-ID: <87edr9tq0c.fsf@redhat.com> (raw)
In-Reply-To: <20230130044518.3322695-7-thiago.bauermann@linaro.org>

Thiago Jung Bauermann via Gdb-patches <gdb-patches@sourceware.org>
writes:

> gdbserver added the concept of target description IDs to the remote
> protocol and uses them in the threads list XML and in the 'T AA' stop
> reply packet.  It also allows fetching a target description with a given
> ID.  This patch is for the GDB-side support.  The target descriptions
> obtained this way aren't yet used but will be in the next patch.
>
> In the DTD for the threads list XML, add a "tdesc" attribute to the
> <thread> node.  A tdesc_id field is added to the stop_reply and
> thread_item structs.  An m_remote member is added to the
> threads_listing_context struct, and to simplify its initialisation a
> constructor is added as well.  This is to provide access to the remote
> state in start_thread.
>
> Finally, the remote_state object keeps a map of the target descriptions
> that have been received from the target, keyed by their ID.  There are
> also methods to get a target description given its ID, and to fetch target
> descriptions for IDs that were mentioned by gdbserver but not yet
> retrieved by GDB.  The latter gets called after parsing the response of
> qXfer:threads:read and of the stop reply packet.
> ---
>  gdb/features/threads.dtd |  1 +
>  gdb/remote.c             | 85 +++++++++++++++++++++++++++++++++++++++-
>  gdb/xml-tdesc.c          | 27 ++++++++++---
>  gdb/xml-tdesc.h          |  6 +++
>  4 files changed, 112 insertions(+), 7 deletions(-)
>
> diff --git a/gdb/features/threads.dtd b/gdb/features/threads.dtd
> index 036b2ce58837..3102d1352978 100644
> --- a/gdb/features/threads.dtd
> +++ b/gdb/features/threads.dtd
> @@ -11,3 +11,4 @@
>  
>  <!ATTLIST thread id CDATA #REQUIRED>
>  <!ATTLIST thread core CDATA #IMPLIED>
> +<!ATTLIST thread tdesc CDATA #IMPLIED>
> diff --git a/gdb/remote.c b/gdb/remote.c
> index 218bca30d047..f1d1944414c3 100644
> --- a/gdb/remote.c
> +++ b/gdb/remote.c
> @@ -80,6 +80,7 @@
>  #include <unordered_map>
>  #include "async-event.h"
>  #include "gdbsupport/selftest.h"
> +#include "xml-tdesc.h"
>  
>  /* The remote target.  */
>  
> @@ -238,6 +239,16 @@ class remote_state
>    /* Get the remote arch state for GDBARCH.  */
>    struct remote_arch_state *get_remote_arch_state (struct gdbarch *gdbarch);
>  
> +  /* Add new ID to the target description list.  The corresponding XML will be
> +     requested soon.  */
> +  void add_tdesc_id (ULONGEST id);

I'm wondering why this function is needed?  Could we not just have
get_tdesc take a remote_target* argument, and fetch the descriptions on
demand?  This would also allow fetch_unknown_tdescs to be removed I
think, as well as the remote_target* inside threads_listing_context.

> +
> +  /* Get the target description corresponding to remote protocol ID.  */
> +  const target_desc *get_tdesc (ULONGEST id) const;
> +
> +  /* Get the target descriptions we don't know about from the target.  */
> +  void fetch_unknown_tdescs (remote_target *remote);
> +
>  public: /* data */
>  
>    /* A buffer to use for incoming packets, and its current size.  The
> @@ -387,6 +398,10 @@ class remote_state
>       support multi-process.  */
>    std::unordered_map<struct gdbarch *, remote_arch_state>
>      m_arch_states;
> +
> +  /* The target descriptions that have been received from the target.  The key
> +     is the ID used to reference it in the remote protocol.  */
> +  std::unordered_map<ULONGEST, const target_desc *> m_tdescs;

Who owns the objects pointed too by this data structure?  From my
reading of the code I suspect they are owned by the remote_state, in
which case we should possibly be deleting the objects in
remote_state::~remote_state.

The only problem with this would be, what happens to any threads that
reference a target description within a remote connection that is close,
and thus the referenced target description is deleted....

... having just run a test it appears that when we disconnect from a
remote target, the remote target itself (and the associated
remote_state) is deleted first, and then we delete the threads of
inferiors running on that target.  That means that if we did delete the
target descriptions in ~remote_state, then we would, for a time, be in a
situation where the thread_info referenced a deleted target description.

I'm not sure how easy that would be to fix, maybe we can just add some
code in remote_unpush_target before the call to
inferior::pop_all_targets_at_and_above?

Anyway, I think the first attempt should be to make the m_tdescs data
structure be:

  std::unordered_map<ULONGEST, std::unique_ptr<const target_desc>> m_tdescs;

>  };
>  
>  static const target_info remote_target_info = {
> @@ -1009,6 +1024,9 @@ struct stop_reply : public notif_event
>       fetch them is avoided).  */
>    std::vector<cached_reg_t> regcache;
>  
> +  /* The target description ID communicated in the stop reply packet.  */
> +  gdb::optional<ULONGEST> tdesc_id;
> +
>    enum target_stop_reason stop_reason;
>  
>    CORE_ADDR watch_data_address;
> @@ -3689,6 +3707,9 @@ struct thread_item
>  
>    /* The thread handle associated with the thread.  */
>    gdb::byte_vector thread_handle;
> +
> +  /* The ID of the thread's target description, if provided.  */
> +  gdb::optional<ULONGEST> tdesc_id;
>  };
>  
>  /* Context passed around to the various methods listing remote
> @@ -3697,6 +3718,12 @@ struct thread_item
>  
>  struct threads_listing_context
>  {
> +  threads_listing_context (remote_target *remote)
> +    : m_remote (remote)
> +  {}
> +
> +  DISABLE_COPY_AND_ASSIGN (threads_listing_context);
> +
>    /* Return true if this object contains an entry for a thread with ptid
>       PTID.  */
>  
> @@ -3733,6 +3760,9 @@ struct threads_listing_context
>  
>    /* The threads found on the remote target.  */
>    std::vector<thread_item> items;
> +
> +  /* The remote target associated with this context.  */
> +  remote_target *m_remote;

The GDB style reserves the 'm_' prefix for private member variables.
Ideally I'd prefer m_remote be made private, and then add a 'remote()'
member function to return the pointer.  Though if my comment above is
correct then I think this new field could be dropped.

>  };
>  
>  static int
> @@ -3814,6 +3844,13 @@ start_thread (struct gdb_xml_parser *parser,
>    attr = xml_find_attribute (attributes, "handle");
>    if (attr != NULL)
>      item.thread_handle = hex2bin ((const char *) attr->value.get ());
> +
> +  attr = xml_find_attribute (attributes, "tdesc");
> +  if (attr != NULL)

s/NULL/nullptr/

> +    {
> +      item.tdesc_id = *(ULONGEST *) attr->value.get ();
> +      data->m_remote->get_remote_state ()->add_tdesc_id (*item.tdesc_id);
> +    }
>  }
>  
>  static void
> @@ -3833,6 +3870,7 @@ const struct gdb_xml_attribute thread_attributes[] = {
>    { "core", GDB_XML_AF_OPTIONAL, gdb_xml_parse_attr_ulongest, NULL },
>    { "name", GDB_XML_AF_OPTIONAL, NULL, NULL },
>    { "handle", GDB_XML_AF_OPTIONAL, NULL, NULL },
> +  { "tdesc", GDB_XML_AF_OPTIONAL, gdb_xml_parse_attr_ulongest, NULL },

Ideally s/NULL/nullptr/ here too, but this one's clearly a bit odd as
we're in a table surrounded by legacy code.  But I think I'd still use
nullptr in preference.

Thanks,
Andrew

>    { NULL, GDB_XML_AF_NONE, NULL, NULL }
>  };
>  
> @@ -3870,6 +3908,7 @@ remote_target::remote_get_threads_with_qxfer (threads_listing_context *context)
>  	{
>  	  gdb_xml_parse_quick (_("threads"), "threads.dtd",
>  			       threads_elements, xml->data (), context);
> +	  get_remote_state ()->fetch_unknown_tdescs (this);
>  	}
>  
>        return 1;
> @@ -3937,7 +3976,7 @@ has_single_non_exited_thread (inferior *inf)
>  void
>  remote_target::update_thread_list ()
>  {
> -  struct threads_listing_context context;
> +  struct threads_listing_context context (this);
>    int got_list = 0;
>  
>    /* We have a few different mechanisms to fetch the thread list.  Try
> @@ -7223,7 +7262,11 @@ remote_notif_stop_parse (remote_target *remote,
>  			 struct notif_client *self, const char *buf,
>  			 struct notif_event *event)
>  {
> -  remote->remote_parse_stop_reply (buf, (struct stop_reply *) event);
> +  struct stop_reply *stop_reply = (struct stop_reply *) event;
> +
> +  remote->remote_parse_stop_reply (buf, stop_reply);
> +
> +  stop_reply->rs->fetch_unknown_tdescs (remote);
>  }
>  
>  static void
> @@ -7516,6 +7559,36 @@ strprefix (const char *p, const char *pend, const char *prefix)
>    return *prefix == '\0';
>  }
>  
> +void
> +remote_state::add_tdesc_id (ULONGEST id)
> +{
> +  /* Check whether the ID was already added.  */
> +  if (m_tdescs.find (id) != m_tdescs.cend ())
> +    return;
> +
> +  m_tdescs[id] = nullptr;
> +}
> +
> +const target_desc *
> +remote_state::get_tdesc (ULONGEST id) const
> +{
> +  auto found = m_tdescs.find (id);
> +
> +  /* Check if the given ID was already provided.  */
> +  if (found == m_tdescs.cend ())
> +    return nullptr;
> +
> +  return found->second;
> +}
> +
> +void
> +remote_state::fetch_unknown_tdescs (remote_target *remote)
> +{
> +  for (auto &pair : m_tdescs)
> +    if (pair.second == nullptr)
> +      m_tdescs[pair.first] = target_read_description_xml (remote, pair.first);
> +}
> +
>  /* Parse the stop reply in BUF.  Either the function succeeds, and the
>     result is stored in EVENT, or throws an error.  */
>  
> @@ -7674,6 +7747,14 @@ Packet: '%s'\n"),
>  	      event->ws.set_thread_created ();
>  	      p = strchrnul (p1 + 1, ';');
>  	    }
> +	  else if (strprefix (p, p1, "tdesc"))
> +	    {
> +	      ULONGEST tdesc_id;
> +
> +	      p = unpack_varlen_hex (++p1, &tdesc_id);
> +	      event->rs->add_tdesc_id (tdesc_id);
> +	      event->tdesc_id = tdesc_id;
> +	    }
>  	  else
>  	    {
>  	      ULONGEST pnum;
> diff --git a/gdb/xml-tdesc.c b/gdb/xml-tdesc.c
> index ba7154c5d56f..302863e12365 100644
> --- a/gdb/xml-tdesc.c
> +++ b/gdb/xml-tdesc.c
> @@ -698,14 +698,13 @@ fetch_available_features_from_target (const char *name, target_ops *ops)
>  }
>  \f
>  
> -/* Read an XML target description using OPS.  Parse it, and return the
> -   parsed description.  */
> +/* Actual implementation of the target_read_description_xml variants.  */
>  
> -const struct target_desc *
> -target_read_description_xml (struct target_ops *ops)
> +static const struct target_desc *
> +target_read_description_xml (struct target_ops *ops, const char *desc_name)
>  {
>    gdb::optional<gdb::char_vector> tdesc_str
> -    = fetch_available_features_from_target ("target.xml", ops);
> +    = fetch_available_features_from_target (desc_name, ops);
>    if (!tdesc_str)
>      return NULL;
>  
> @@ -717,6 +716,24 @@ target_read_description_xml (struct target_ops *ops)
>    return tdesc_parse_xml (tdesc_str->data (), fetch_another);
>  }
>  
> +/* See xml-tdesc.h.  */
> +
> +const struct target_desc *
> +target_read_description_xml (struct target_ops *ops)
> +{
> +  return target_read_description_xml (ops, "target.xml");
> +}
> +
> +/* See xml-tdesc.h.  */
> +
> +const struct target_desc *
> +target_read_description_xml (struct target_ops *ops, ULONGEST id)
> +{
> +  std::string desc_name = string_printf ("target-id-%" PRIu64 ".xml", id);
> +
> +  return target_read_description_xml (ops, desc_name.c_str ());
> +}
> +
>  /* Fetches an XML target description using OPS,  processing
>     includes, but not parsing it.  Used to dump whole tdesc
>     as a single XML file.  */
> diff --git a/gdb/xml-tdesc.h b/gdb/xml-tdesc.h
> index 0fbfc7e043e9..c7cc97c5dfc0 100644
> --- a/gdb/xml-tdesc.h
> +++ b/gdb/xml-tdesc.h
> @@ -38,6 +38,12 @@ const struct target_desc *file_read_description_xml (const char *filename);
>  
>  const struct target_desc *target_read_description_xml (struct target_ops *);
>  
> +/* Read an XML target description with the given ID using OPS.  Parse it, and
> +   return the parsed description.  */
> +
> +const struct target_desc *target_read_description_xml (struct target_ops *ops,
> +						       ULONGEST id);
> +
>  /* Fetches an XML target description using OPS, processing includes,
>     but not parsing it.  Used to dump whole tdesc as a single XML file.
>     Returns the description on success, and a disengaged optional


  parent reply	other threads:[~2023-02-01 14:32 UTC|newest]

Thread overview: 94+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-01-30  4:45 [PATCH v3 0/8] gdbserver improvements for AArch64 SVE support Thiago Jung Bauermann
2023-01-30  4:45 ` [PATCH v3 1/8] gdbserver: Add assert in find_register_by_number Thiago Jung Bauermann
2023-01-31 17:05   ` Simon Marchi
2023-01-31 19:49     ` Thiago Jung Bauermann
2023-02-01 15:43       ` Simon Marchi
2023-01-30  4:45 ` [PATCH v3 2/8] gdbserver: Add PID parameter to linux_get_auxv and linux_get_hwcap Thiago Jung Bauermann
2023-02-01  9:07   ` Luis Machado
2023-02-01 10:54   ` Andrew Burgess
2023-02-01 16:01     ` Simon Marchi
2023-02-01 19:33       ` Thiago Jung Bauermann
2023-02-01 19:53         ` Simon Marchi
2023-02-01 21:55           ` Thiago Jung Bauermann
2023-02-06 19:54   ` Pedro Alves
2023-02-06 20:16     ` Simon Marchi
2023-02-07 15:19       ` Pedro Alves
2023-02-07 21:47         ` Thiago Jung Bauermann
2023-02-09  1:31           ` Simon Marchi
2023-02-10  3:54             ` Thiago Jung Bauermann
2023-02-07 22:28     ` Thiago Jung Bauermann
2023-01-30  4:45 ` [PATCH v3 3/8] gdbserver/linux-aarch64: Factor out function to get aarch64_features Thiago Jung Bauermann
2023-02-01  8:59   ` Luis Machado
2023-02-01 16:04     ` Simon Marchi
2023-02-01 22:13       ` Thiago Jung Bauermann
2023-01-30  4:45 ` [PATCH v3 4/8] gdbserver/linux-aarch64: When thread stops, update its target description Thiago Jung Bauermann
2023-02-01  9:05   ` Luis Machado
2023-02-01 11:06   ` Andrew Burgess
2023-02-01 16:21     ` Simon Marchi
2023-02-01 16:32       ` Luis Machado
2023-02-02  2:54         ` Thiago Jung Bauermann
2023-02-02  3:47           ` Simon Marchi
2023-02-03  3:47             ` Thiago Jung Bauermann
2023-02-03 11:13               ` Luis Machado
2023-02-04 15:26                 ` Thiago Jung Bauermann
2023-02-03 11:11             ` Luis Machado
2023-02-04 15:21               ` Thiago Jung Bauermann
2023-02-06  9:07                 ` Luis Machado
2023-02-06 12:15                   ` Thiago Jung Bauermann
2023-02-06 20:29                 ` Pedro Alves
2023-02-07  8:11                   ` Luis Machado
2023-02-07 14:39                     ` Thiago Jung Bauermann
2023-02-03 10:57           ` Luis Machado
2023-02-04  6:18             ` Thiago Jung Bauermann
2023-02-06 20:26           ` Pedro Alves
2023-02-07 21:06             ` Thiago Jung Bauermann
2023-02-09  2:46               ` Simon Marchi
2023-02-10  3:29                 ` Thiago Jung Bauermann
2023-02-10 14:56                   ` Luis Machado
2023-02-10 15:04                     ` Tom Tromey
2023-02-10 15:28                       ` Luis Machado
2023-02-10 17:26                       ` Thiago Jung Bauermann
2023-02-10 21:01                         ` Simon Marchi
2023-01-30  4:45 ` [PATCH v3 5/8] gdbserver: Transmit target description ID in thread list and stop reply Thiago Jung Bauermann
2023-01-30 12:52   ` Eli Zaretskii
2023-01-30 14:05     ` Thiago Jung Bauermann
2023-02-01  9:39   ` Luis Machado
2023-02-01 12:07   ` Andrew Burgess
2023-02-01 13:03     ` Eli Zaretskii
2023-02-01 17:37     ` Simon Marchi
2023-02-02 20:36       ` Thiago Jung Bauermann
2023-02-02 20:56         ` Simon Marchi
2023-02-01 20:46     ` Simon Marchi
2023-02-02 21:43       ` Thiago Jung Bauermann
2023-02-01 14:51   ` Andrew Burgess
2023-02-01 17:03     ` Simon Marchi
2023-02-02 19:52       ` Thiago Jung Bauermann
2023-02-02 20:51         ` Simon Marchi
2023-02-03  2:44           ` Thiago Jung Bauermann
2023-02-03 16:29             ` Andrew Burgess
2023-02-04  6:08               ` Thiago Jung Bauermann
2023-02-03 11:22       ` Luis Machado
2023-02-03 12:50         ` Simon Marchi
2023-01-30  4:45 ` [PATCH v3 6/8] gdb/remote: Parse tdesc field in stop reply and threads list XML Thiago Jung Bauermann
2023-02-01  9:52   ` Luis Machado
2023-02-05  0:06     ` Thiago Jung Bauermann
2023-02-06  9:10       ` Luis Machado
2023-02-01 14:32   ` Andrew Burgess [this message]
2023-02-01 19:50     ` Simon Marchi
2023-02-01 20:16       ` Simon Marchi
2023-02-03 11:27         ` Luis Machado
2023-02-03 13:19           ` Simon Marchi
2023-02-03 16:33             ` Andrew Burgess
2023-01-30  4:45 ` [PATCH v3 7/8] gdb/aarch64: Detect vector length changes when debugging remotely Thiago Jung Bauermann
2023-02-01  9:58   ` Luis Machado
2023-02-01 15:26   ` Andrew Burgess
2023-02-01 20:20     ` Simon Marchi
2023-02-03 11:31       ` Luis Machado
2023-02-03 16:38       ` Andrew Burgess
2023-02-03 19:07         ` Simon Marchi
2023-01-30  4:45 ` [PATCH v3 8/8] gdb/testsuite: Add test to exercise multi-threaded AArch64 SVE inferiors Thiago Jung Bauermann
2023-02-01 10:10   ` Luis Machado
2023-02-06 19:11 ` [PATCH v3 0/8] gdbserver improvements for AArch64 SVE support Pedro Alves
2023-02-06 20:05   ` Simon Marchi
2023-02-06 21:06     ` Pedro Alves
2023-02-07 13:49       ` Simon Marchi

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