diff mbox

[PATCHv3,1/2] gdbserver: Add mechanism to prevent sending T stop packets

Message ID 27befec6c761c43f2e1a9e59403644c198cbd75b.1583149853.git.andrew.burgess@embecosm.com
State New
Headers show

Commit Message

Andrew Burgess March 2, 2020, 11:54 a.m. UTC
There is a developer only feature in gdbserver that provides a
command line option --disable-packet that prevents some packets from
being sent, which is used to increase test coverage within GDB.

This commit extends this mechanism to prevent GDBserver from sending
the T stop reply packets, instead limiting GDBserver to only send the
S stop reply packets.

The S stop reply packet is part of the older target control mechanism,
which has design flaws that were worked around with the introduction
of the newer target control mechanism, which uses the T stop reply
packet.

Limiting GDBserver to use S stop packets instead of T stop packets
will, inevitably, mean that GDBserver doesn't function correctly in
many cases involving multiple threads, however, I don't think this is
too important, this is a developer only feature, intended to allow us
to test GDB.

A new test that makes use of this feature will be added in the next
commit.

gdbserver/ChangeLog:

	* remote-utils.cc (prepare_resume_reply): Add ability to convert T
	reply into an S reply.
	* server.cc (disable_packet_T): New global.
	(captured_main): Set new global when appropriate.
	* server.h (disable_packet_T): Declare.
---
 gdbserver/ChangeLog       |  8 ++++++++
 gdbserver/remote-utils.cc | 20 ++++++++++++++++++++
 gdbserver/server.cc       |  3 +++
 gdbserver/server.h        |  1 +
 4 files changed, 32 insertions(+)

Comments

Pedro Alves March 2, 2020, 12:24 p.m. UTC | #1
On 3/2/20 11:54 AM, Andrew Burgess wrote:
> There is a developer only feature in gdbserver that provides a
> command line option --disable-packet that prevents some packets from
> being sent, which is used to increase test coverage within GDB.
> 
> This commit extends this mechanism to prevent GDBserver from sending
> the T stop reply packets, instead limiting GDBserver to only send the
> S stop reply packets.
> 
> The S stop reply packet is part of the older target control mechanism,
> which has design flaws that were worked around with the introduction
> of the newer target control mechanism, which uses the T stop reply
> packet.
> 
> Limiting GDBserver to use S stop packets instead of T stop packets
> will, inevitably, mean that GDBserver doesn't function correctly in
> many cases involving multiple threads, however, I don't think this is
> too important, this is a developer only feature, intended to allow us
> to test GDB.
> 
> A new test that makes use of this feature will be added in the next
> commit.
> 
> gdbserver/ChangeLog:
> 
> 	* remote-utils.cc (prepare_resume_reply): Add ability to convert T
> 	reply into an S reply.
> 	* server.cc (disable_packet_T): New global.
> 	(captured_main): Set new global when appropriate.
> 	* server.h (disable_packet_T): Declare.

OK.

Thanks,
Pedro Alves
diff mbox

Patch

diff --git a/gdbserver/remote-utils.cc b/gdbserver/remote-utils.cc
index 6b547493a71..1c211e25720 100644
--- a/gdbserver/remote-utils.cc
+++ b/gdbserver/remote-utils.cc
@@ -1204,6 +1204,26 @@  prepare_resume_reply (char *buf, ptid_t ptid,
 	else
 	  sprintf (buf, "T%02x", status->value.sig);
 
+	if (disable_packet_T)
+	  {
+	    /* This is a bit (OK, a lot) of a kludge, however, this isn't
+	       really a user feature, but exists only so GDB can use the
+	       gdbserver to test handling of the 'S' stop reply packet, so
+	       we would rather this code be as simple as possible.
+
+	       By this point we've started to build the 'T' stop packet,
+	       and it should look like 'Txx....' where 'x' is a hex digit.
+	       An 'S' stop packet always looks like 'Sxx', so all we do
+	       here is convert the buffer from a T packet to an S packet
+	       and the avoid adding any extra content by breaking out.  */
+	    gdb_assert (*buf == 'T');
+	    gdb_assert (isxdigit (*(buf + 1)));
+	    gdb_assert (isxdigit (*(buf + 2)));
+	    *buf = 'S';
+	    *(buf + 3) = '\0';
+	    break;
+	  }
+
 	buf += strlen (buf);
 
 	saved_thread = current_thread;
diff --git a/gdbserver/server.cc b/gdbserver/server.cc
index a4cb1eb4181..43962adc86c 100644
--- a/gdbserver/server.cc
+++ b/gdbserver/server.cc
@@ -130,6 +130,7 @@  bool disable_packet_vCont;
 bool disable_packet_Tthread;
 bool disable_packet_qC;
 bool disable_packet_qfThreadInfo;
+bool disable_packet_T;
 
 static unsigned char *mem_buf;
 
@@ -3649,6 +3650,8 @@  captured_main (int argc, char *argv[])
 		disable_packet_qC = true;
 	      else if (strcmp ("qfThreadInfo", tok) == 0)
 		disable_packet_qfThreadInfo = true;
+	      else if (strcmp ("T", tok) == 0)
+		disable_packet_T = true;
 	      else if (strcmp ("threads", tok) == 0)
 		{
 		  disable_packet_vCont = true;
diff --git a/gdbserver/server.h b/gdbserver/server.h
index 3c286862349..5ef48b62c62 100644
--- a/gdbserver/server.h
+++ b/gdbserver/server.h
@@ -76,6 +76,7 @@  extern bool disable_packet_vCont;
 extern bool disable_packet_Tthread;
 extern bool disable_packet_qC;
 extern bool disable_packet_qfThreadInfo;
+extern bool disable_packet_T;
 
 extern bool run_once;
 extern bool non_stop;