[PATCH v7 1/7] Identify remote fork event support

Don Breazeal
2015-04-10T17:10:13Z

Hi Pedro,
This patch is mostly unchanged from the previous version, except for
moving the (updated) documentation pieces to a separate patch.

The remaining code portions of this patch were approved here:
https://sourceware.org/ml/gdb-patches/2015-03/msg00896.html

On 3/27/2015 4:14 AM, Pedro Alves wrote:
> On 03/26/2015 07:00 PM, Don Breazeal wrote:
>> On 3/24/2015 3:57 AM, Pedro Alves wrote:
>>> On 03/17/2015 08:56 PM, Don Breazeal wrote:

>> --- a/gdb/doc/gdb.texinfo
>> +++ b/gdb/doc/gdb.texinfo
>> @@ -35812,6 +35812,18 @@ extensions unless the stub also reports that it supports them by
>> including @samp{multiprocess+} in its @samp{qSupported} reply.
>> @xref{multiprocess extensions}, for details.
>>
>> +@item fork-events
>> +This feature indicates whether @value{GDBN} supports fork event
>> +extensions to the remote protocol. @value{GDBN} does not use such
>> +extensions unless the stub also reports that it supports them by
>> +including @samp{fork-events+} in its @samp{qSupported} reply.
>> +
>> +@item vfork-events
>> +This feature indicates whether @value{GDBN} supports vfork event
>> +extensions to the remote protocol. @value{GDBN} does not use such
>> +extensions unless the stub also reports that it supports them by
>> +including @samp{vfork-events+} in its @samp{qSupported} reply.
>> +
>> @item xmlRegisters
>> This feature indicates that @value{GDBN} supports the XML target
>> description. If the stub sees @samp{xmlRegisters=} with target
>> diff --git a/gdb/gdbserver/linux-low.c b/gdb/gdbserver/linux-low.c
>> index e4c5420..06ac673 100644
>
> You'll need to update the tables below, where it reads:
>
> "These are the currently defined stub features and their properties"
>
> and:
>
> "These are the currently defined stub features, in more detail"
>
> and also, mention the new commands in:
>
> "For each packet @var{name}, the command to enable or disable the
> packet is @code{set remote @var{name}-packet}. The available settings
> are:"

I have moved all the documentation pieces into a separate patch, and
incorporated these changes into that patch.

Thanks!
--Don

This patch implements a mechanism for GDB to determine whether fork
events are supported in gdbserver. This is a preparatory patch for
remote fork and exec event support.

Two new RSP packets are defined to represent fork and vfork event
support. These packets are used just like PACKET_multiprocess_feature
to denote whether the corresponding event is supported. GDB sends
fork-events+ and vfork-events+ to gdbserver to inquire about fork
event support. If the response enables these packets, then GDB
knows that gdbserver supports the corresponding events and will
enable them.

Target functions used to query for support are included along with
each new packet.

In order for gdbserver to know whether the events are supported at the
point where the qSupported packet arrives, the code in nat/linux-ptrace.c
had to be reorganized. Previously it would test for fork/exec event
support, then enable the events using the pid of the inferior. When the
qSupported packet arrives there may not be an inferior. So the mechanism
was split into two parts: a function that checks whether the events are
supported, called when gdbserver starts up, and another that enables the
events when the inferior stops for the first time.

Another gdbserver change was to add some global variables similar to
multi_process, one per new packet. These are used to control whether
the corresponding fork events are enabled. If GDB does not inquire
about the event support in the qSupported packet, then gdbserver will
not set these "report the event" flags. If the flags are not set, the
events are ignored like they were in the past. Thus, gdbserver will
never send fork event notification to an older GDB that doesn't
recognize fork events.

Tested on Ubuntu x64, native/remote/extended-remote, and as part of
subsequent patches in the series.

gdb/gdbserver/
2015-04-08 Don Breazeal <donb@codesourcery.com>

* linux-low.c (linux_supports_fork_events): New function.
(linux_supports_vfork_events): New function.
(linux_target_ops): Initialize new structure members.
(initialize_low): Call linux_check_ptrace_features.
* lynx-low.c (lynx_target_ops): Initialize new structure
members.
* server.c (report_fork_events, report_vfork_events):
New global flags.
(handle_query): Add new features to qSupported packet and
response.
(captured_main): Initialize new global variables.
* target.h (struct target_ops) <supports_fork_events>:
New member.
<supports_vfork_events>: New member.
(target_supports_fork_events): New macro.
(target_supports_vfork_events): New macro.
* win32-low.c (win32_target_ops): Initialize new structure
members.

gdb/
2015-04-08 Don Breazeal <donb@codesourcery.com>

* nat/linux-ptrace.c (linux_check_ptrace_features): Change
from static to extern.
* nat/linux-ptrace.h (linux_check_ptrace_features): Declare.
* remote.c (anonymous enum): <PACKET_fork_event_feature,
* PACKET_vfork_event_feature>: New enumeration constants.
(remote_protocol_features): Add table entries for new packets.
(remote_query_supported): Add new feature queries to qSupported
packet.
(_initialize_remote): Exempt new packets from the requirement
to have 'set remote' commands.

---
gdb/gdbserver/linux-low.c | 21 +++++++++++++++++++++
gdb/gdbserver/lynx-low.c | 2 ++
gdb/gdbserver/server.c | 22 ++++++++++++++++++++++
gdb/gdbserver/target.h | 14 ++++++++++++++
gdb/gdbserver/win32-low.c | 2 ++
gdb/nat/linux-ptrace.c | 2 +-
gdb/nat/linux-ptrace.h | 1 +
gdb/remote.c | 26 ++++++++++++++++++++++++++
8 files changed, 89 insertions(+), 1 deletion(-)

diff --git a/gdb/gdbserver/linux-low.c b/gdb/gdbserver/linux-low.c
index e4c5420..06ac673 100644
--- a/gdb/gdbserver/linux-low.c
+++ b/gdb/gdbserver/linux-low.c
@@ -5421,6 +5421,22 @@ linux_supports_multi_process (void)
return 1;
}

+/* Check if fork events are supported. */
+
+static int
+linux_supports_fork_events (void)
+{
+ return linux_supports_tracefork ();
+}
+
+/* Check if vfork events are supported. */
+
+static int
+linux_supports_vfork_events (void)
+{
+ return linux_supports_tracefork ();
+}
+
static int
linux_supports_disable_randomization (void)
{
@@ -6393,6 +6409,8 @@ static struct target_ops linux_target_ops = {
linux_async,
linux_start_non_stop,
linux_supports_multi_process,
+ linux_supports_fork_events,
+ linux_supports_vfork_events,
#ifdef USE_THREAD_DB
thread_db_handle_monitor_command,
#else
@@ -6469,4 +6487,7 @@ initialize_low (void)
sigaction (SIGCHLD, &sigchld_action, NULL);

initialize_low_arch ();
+
+ /* Enable extended ptrace events. */
+ linux_check_ptrace_features ();
}
diff --git a/gdb/gdbserver/lynx-low.c b/gdb/gdbserver/lynx-low.c
index 2f85829..687cce0 100644
--- a/gdb/gdbserver/lynx-low.c
+++ b/gdb/gdbserver/lynx-low.c
@@ -758,6 +758,8 @@ static struct target_ops lynx_target_ops = {
NULL, /* async */
NULL, /* start_non_stop */
NULL, /* supports_multi_process */
+ NULL, /* supports_fork_events */
+ NULL, /* supports_vfork_events */
NULL, /* handle_monitor_command */
};

diff --git a/gdb/gdbserver/server.c b/gdb/gdbserver/server.c
index 3408ef7..c609db9 100644
--- a/gdb/gdbserver/server.c
+++ b/gdb/gdbserver/server.c
@@ -57,6 +57,8 @@ static int exit_requested;
int run_once;

int multi_process;
+int report_fork_events;
+int report_vfork_events;
int non_stop;
int swbreak_feature;
int hwbreak_feature;
@@ -1992,6 +1994,18 @@ handle_query (char *own_buf, int packet_len, int *new_packet_len_p)
if (target_supports_stopped_by_hw_breakpoint ())
hwbreak_feature = 1;
}
+ else if (strcmp (p, "fork-events+") == 0)
+ {
+ /* GDB supports and wants fork events if possible. */
+ if (target_supports_fork_events ())
+ report_fork_events = 1;
+ }
+ else if (strcmp (p, "vfork-events+") == 0)
+ {
+ /* GDB supports and wants vfork events if possible. */
+ if (target_supports_vfork_events ())
+ report_vfork_events = 1;
+ }
else
target_process_qsupported (p);

@@ -2042,6 +2056,12 @@ handle_query (char *own_buf, int packet_len, int *new_packet_len_p)
if (target_supports_multi_process ())
strcat (own_buf, ";multiprocess+");

+ if (target_supports_fork_events ())
+ strcat (own_buf, ";fork-events+");
+
+ if (target_supports_vfork_events ())
+ strcat (own_buf, ";vfork-events+");
+
if (target_supports_non_stop ())
strcat (own_buf, ";QNonStop+");

@@ -3414,6 +3434,8 @@ captured_main (int argc, char *argv[])

noack_mode = 0;
multi_process = 0;
+ report_fork_events = 0;
+ report_vfork_events = 0;
/* Be sure we're out of tfind mode. */
current_traceframe = -1;
cont_thread = null_ptid;
diff --git a/gdb/gdbserver/target.h b/gdb/gdbserver/target.h
index 126c861..dc51627 100644
--- a/gdb/gdbserver/target.h
+++ b/gdb/gdbserver/target.h
@@ -277,6 +277,12 @@ struct target_ops
/* Returns true if the target supports multi-process debugging. */
int (*supports_multi_process) (void);

+ /* Returns true if fork events are supported. */
+ int (*supports_fork_events) (void);
+
+ /* Returns true if vfork events are supported. */
+ int (*supports_vfork_events) (void);
+
/* If not NULL, target-specific routine to process monitor command.
Returns 1 if handled, or 0 to perform default processing. */
int (*handle_monitor_command) (char *);
@@ -408,6 +414,14 @@ void set_target_ops (struct target_ops *);

int kill_inferior (int);

+#define target_supports_fork_events() \
+ (the_target->supports_fork_events ? \
+ (*the_target->supports_fork_events) () : 0)
+
+#define target_supports_vfork_events() \
+ (the_target->supports_vfork_events ? \
+ (*the_target->supports_vfork_events) () : 0)
+
#define detach_inferior(pid) \
(*the_target->detach) (pid)

diff --git a/gdb/gdbserver/win32-low.c b/gdb/gdbserver/win32-low.c
index 6c86765..5f50e46 100644
--- a/gdb/gdbserver/win32-low.c
+++ b/gdb/gdbserver/win32-low.c
@@ -1827,6 +1827,8 @@ static struct target_ops win32_target_ops = {
NULL, /* async */
NULL, /* start_non_stop */
NULL, /* supports_multi_process */
+ NULL, /* supports_fork_events */
+ NULL, /* supports_vfork_events */
NULL, /* handle_monitor_command */
NULL, /* core_of_thread */
NULL, /* read_loadmap */
diff --git a/gdb/nat/linux-ptrace.c b/gdb/nat/linux-ptrace.c
index 2244d9d..aba3da8 100644
--- a/gdb/nat/linux-ptrace.c
+++ b/gdb/nat/linux-ptrace.c
@@ -337,7 +337,7 @@ static void linux_test_for_exitkill (int child_pid);

/* Determine ptrace features available on this target. */

-static void
+void
linux_check_ptrace_features (void)
{
int child_pid, ret, status;
diff --git a/gdb/nat/linux-ptrace.h b/gdb/nat/linux-ptrace.h
index 8354a4d..03d98c9 100644
--- a/gdb/nat/linux-ptrace.h
+++ b/gdb/nat/linux-ptrace.h
@@ -149,6 +149,7 @@ extern void linux_ptrace_attach_fail_reason (pid_t pid, struct buffer *buffer);
extern char *linux_ptrace_attach_fail_reason_string (ptid_t ptid, int err);

extern void linux_ptrace_init_warnings (void);
+extern void linux_check_ptrace_features (void);
extern void linux_enable_event_reporting (pid_t pid, int attached);
extern void linux_disable_event_reporting (pid_t pid);
extern int linux_supports_tracefork (void);
diff --git a/gdb/remote.c b/gdb/remote.c
index 69a67a8..0006618 100644
--- a/gdb/remote.c
+++ b/gdb/remote.c
@@ -1341,6 +1341,12 @@ enum {
/* Support for hwbreak+ feature. */
PACKET_hwbreak_feature,

+ /* Support for fork events. */
+ PACKET_fork_event_feature,
+
+ /* Support for vfork events. */
+ PACKET_vfork_event_feature,
+
PACKET_MAX
};

@@ -4040,6 +4046,10 @@ static const struct protocol_feature remote_protocol_features[] = {
PACKET_Qbtrace_conf_bts_size },
{ "swbreak", PACKET_DISABLE, remote_supported_packet, PACKET_swbreak_feature },
{ "hwbreak", PACKET_DISABLE, remote_supported_packet, PACKET_hwbreak_feature },
+ { "fork-events", PACKET_DISABLE, remote_supported_packet,
+ PACKET_fork_event_feature },
+ { "vfork-events", PACKET_DISABLE, remote_supported_packet,
+ PACKET_vfork_event_feature },
};

static char *remote_support_xml;
@@ -4118,6 +4128,16 @@ remote_query_supported (void)

q = remote_query_supported_append (q, "qRelocInsn+");

+ if (rs->extended)
+ {
+ if (packet_set_cmd_state (PACKET_fork_event_feature)
+ != AUTO_BOOLEAN_FALSE)
+ q = remote_query_supported_append (q, "fork-events+");
+ if (packet_set_cmd_state (PACKET_vfork_event_feature)
+ != AUTO_BOOLEAN_FALSE)
+ q = remote_query_supported_append (q, "vfork-events+");
+ }
+
q = reconcat (q, "qSupported:", q, (char *) NULL);
putpkt (q);

@@ -12378,6 +12398,12 @@ Show the maximum size of the address (in bits) in a memory packet."), NULL,
add_packet_config_cmd (&remote_protocol_packets[PACKET_hwbreak_feature],
"hwbreak-feature", "hwbreak-feature", 0);

+ add_packet_config_cmd (&remote_protocol_packets[PACKET_fork_event_feature],
+ "fork-event-feature", "fork-event-feature", 0);
+
+ add_packet_config_cmd (&remote_protocol_packets[PACKET_vfork_event_feature],
+ "vfork-event-feature", "vfork-event-feature", 0);
+
/* Assert that we've registered "set remote foo-packet" commands
for all packet configs. */
{
--
1.8.1.1