Fix "Remote 'g' packet reply is too long" problems with multiple inferiors

When debugging two inferiors (or more) against gdbserver, and the
inferiors have different architectures, such as e.g., on x86_64
GNU/Linux and one inferior is 64-bit while the other is 32-bit, then
GDB can get confused with the different architectures in a couple
spots.

In both cases I ran into, GDB incorrectly ended up using the
architecture of whatever happens to be the selected inferior instead
of the architecture of some other given inferior:

#1 - When parsing the expedited registers in stop replies.

#2 - In the default implementation of the target_thread_architecture
     target method.

These resulted in instances of the infamous "Remote 'g' packet reply
is too long" error.  For example, with the test added in this commit,
we get:

~~~
  Continuing.
  Remote 'g' packet reply is too long (expected 440 bytes, got 816 bytes): ad064000000000000[snip]
  (gdb) FAIL: gdb.multi/multi-arch.exp: inf1 event with inf2 selected: continue to hello_loop

  c
  Continuing.
  Truncated register 50 in remote 'g' packet
  (gdb) PASS: gdb.multi/multi-arch.exp: inf2 event with inf1 selected: c
~~~

This commit fixes that.

gdb/ChangeLog:
2017-10-04  Pedro Alves  <palves@redhat.com>

	* remote.c (get_remote_arch_state): New 'gdbarch' parameter.  Use
	it instead of target_gdbarch.
	(get_remote_state, get_remote_packet_size): Adjust
	get_remote_arch_state calls, passing down target_gdbarch
	explicitly.
	(packet_reg_from_regnum, packet_reg_from_pnum): New parameter
	'gdbarch' and use it instead of target_gdbarch.
	(get_memory_packet_size): Adjust get_remote_arch_state calls,
	passing down target_gdbarch explicitly.
	(struct stop_reply) <arch>: New field.
	(remote_parse_stop_reply): Use the stopped thread's architecture,
	not the current inferior's.  Save the architecture in the
	stop_reply.
	(process_stop_reply): Use the stop reply's architecture.
	(process_g_packet, remote_fetch_registers)
	(remote_prepare_to_store, store_registers_using_G)
	(remote_store_registers): Adjust get_remote_arch_state calls,
	using the regcache's architecture.
	(remote_get_trace_status): Adjust get_remote_arch_state calls,
	passing down target_gdbarch explicitly.
	* spu-multiarch.c (spu_thread_architecture): Defer to the target
	beneath instead of calling target_gdbarch.
	* target.c (default_thread_architecture): Use the specified
	inferior's architecture, instead of the current inferior's
	architecture (via target_gdbarch).

gdb/testsuite/ChangeLog:
2017-10-04  Pedro Alves  <palves@redhat.com>

	* gdb.multi/hangout.c: Include <unistd.h>.
	(hangout_loop): New function.
	(main): Call alarm.  Call hangout_loop in a loop.
	* gdb.multi/hello.c: Include <unistd.h>.
	(hello_loop): New function.
	(main): Call alarm.  Call hangout_loop in a loop.
	* gdb.multi/multi-arch.exp: Test running to a breakpoint one
	inferior with the other selected.

1 files changed, 73 insertions, 27 deletions

diff --git a/gdb/remote.c b/gdb/remote.c
index 8c47d06..3ceabcf 100644
--- a/gdb/remote.c
+++ b/gdb/remote.c
@@ -654,11 +654,11 @@ remote_get_noisy_reply ()
 static struct gdbarch_data *remote_gdbarch_data_handle;
 
 static struct remote_arch_state *
-get_remote_arch_state (void)
+get_remote_arch_state (struct gdbarch *gdbarch)
 {
-  gdb_assert (target_gdbarch () != NULL);
+  gdb_assert (gdbarch != NULL);
   return ((struct remote_arch_state *)
-	  gdbarch_data (target_gdbarch (), remote_gdbarch_data_handle));
+	  gdbarch_data (gdbarch, remote_gdbarch_data_handle));
 }
 
 /* Fetch the global remote target state.  */
@@ -671,7 +671,7 @@ get_remote_state (void)
      function which calls getpkt also needs to be mindful of changes
      to rs->buf, but this call limits the number of places which run
      into trouble.  */
-  get_remote_arch_state ();
+  get_remote_arch_state (target_gdbarch ());
 
   return get_remote_state_raw ();
 }
@@ -878,7 +878,7 @@ static long
 get_remote_packet_size (void)
 {
   struct remote_state *rs = get_remote_state ();
-  struct remote_arch_state *rsa = get_remote_arch_state ();
+  remote_arch_state *rsa = get_remote_arch_state (target_gdbarch ());
 
   if (rs->explicit_packet_size)
     return rs->explicit_packet_size;
@@ -887,9 +887,10 @@ get_remote_packet_size (void)
 }
 
 static struct packet_reg *
-packet_reg_from_regnum (struct remote_arch_state *rsa, long regnum)
+packet_reg_from_regnum (struct gdbarch *gdbarch, struct remote_arch_state *rsa,
+			long regnum)
 {
-  if (regnum < 0 && regnum >= gdbarch_num_regs (target_gdbarch ()))
+  if (regnum < 0 && regnum >= gdbarch_num_regs (gdbarch))
     return NULL;
   else
     {
@@ -901,11 +902,12 @@ packet_reg_from_regnum (struct remote_arch_state *rsa, long regnum)
 }
 
 static struct packet_reg *
-packet_reg_from_pnum (struct remote_arch_state *rsa, LONGEST pnum)
+packet_reg_from_pnum (struct gdbarch *gdbarch, struct remote_arch_state *rsa,
+		      LONGEST pnum)
 {
   int i;
 
-  for (i = 0; i < gdbarch_num_regs (target_gdbarch ()); i++)
+  for (i = 0; i < gdbarch_num_regs (gdbarch); i++)
     {
       struct packet_reg *r = &rsa->regs[i];
 
@@ -1049,7 +1051,7 @@ static long
 get_memory_packet_size (struct memory_packet_config *config)
 {
   struct remote_state *rs = get_remote_state ();
-  struct remote_arch_state *rsa = get_remote_arch_state ();
+  remote_arch_state *rsa = get_remote_arch_state (target_gdbarch ());
 
   long what_they_get;
   if (config->fixed_p)
@@ -6364,6 +6366,9 @@ typedef struct stop_reply
 
   struct target_waitstatus ws;
 
+  /* The architecture associated with the expedited registers.  */
+  gdbarch *arch;
+
   /* Expedited registers.  This makes remote debugging a bit more
      efficient for those targets that provide critical registers as
      part of their normal status mechanism (as another roundtrip to
@@ -6838,7 +6843,7 @@ strprefix (const char *p, const char *pend, const char *prefix)
 static void
 remote_parse_stop_reply (char *buf, struct stop_reply *event)
 {
-  struct remote_arch_state *rsa = get_remote_arch_state ();
+  remote_arch_state *rsa = NULL;
   ULONGEST addr;
   const char *p;
   int skipregs = 0;
@@ -7018,9 +7023,47 @@ Packet: '%s'\n"),
 		 reason.  */
 	      if (p_temp == p1)
 		{
-		  struct packet_reg *reg = packet_reg_from_pnum (rsa, pnum);
+		  /* If we haven't parsed the event's thread yet, find
+		     it now, in order to find the architecture of the
+		     reported expedited registers.  */
+		  if (event->ptid == null_ptid)
+		    {
+		      const char *thr = strstr (p1 + 1, ";thread:");
+		      if (thr != NULL)
+			event->ptid = read_ptid (thr + strlen (";thread:"),
+						 NULL);
+		      else
+			event->ptid = magic_null_ptid;
+		    }
+
+		  if (rsa == NULL)
+		    {
+		      inferior *inf = (event->ptid == null_ptid
+				       ? NULL
+				       : find_inferior_ptid (event->ptid));
+		      /* If this is the first time we learn anything
+			 about this process, skip the registers
+			 included in this packet, since we don't yet
+			 know which architecture to use to parse them.
+			 We'll determine the architecture later when
+			 we process the stop reply and retrieve the
+			 target description, via
+			 remote_notice_new_inferior ->
+			 post_create_inferior.  */
+		      if (inf == NULL)
+			{
+			  p = strchrnul (p1 + 1, ';');
+			  p++;
+			  continue;
+			}
+
+		      event->arch = inf->gdbarch;
+		      rsa = get_remote_arch_state (event->arch);
+		    }
+
+		  packet_reg *reg
+		    = packet_reg_from_pnum (event->arch, rsa, pnum);
 		  cached_reg_t cached_reg;
-		  struct gdbarch *gdbarch = target_gdbarch ();
 
 		  if (reg == NULL)
 		    error (_("Remote sent bad register number %s: %s\n\
@@ -7029,13 +7072,13 @@ Packet: '%s'\n"),
 
 		  cached_reg.num = reg->regnum;
 		  cached_reg.data = (gdb_byte *)
-		    xmalloc (register_size (gdbarch, reg->regnum));
+		    xmalloc (register_size (event->arch, reg->regnum));
 
 		  p = p1 + 1;
 		  fieldsize = hex2bin (p, cached_reg.data,
-				       register_size (gdbarch, reg->regnum));
+				       register_size (event->arch, reg->regnum));
 		  p += 2 * fieldsize;
-		  if (fieldsize < register_size (gdbarch, reg->regnum))
+		  if (fieldsize < register_size (event->arch, reg->regnum))
 		    warning (_("Remote reply is too short: %s"), buf);
 
 		  VEC_safe_push (cached_reg_t, event->regcache, &cached_reg);
@@ -7251,7 +7294,7 @@ process_stop_reply (struct stop_reply *stop_reply,
       if (stop_reply->regcache)
 	{
 	  struct regcache *regcache
-	    = get_thread_arch_regcache (ptid, target_gdbarch ());
+	    = get_thread_arch_regcache (ptid, stop_reply->arch);
 	  cached_reg_t *reg;
 	  int ix;
 
@@ -7608,7 +7651,7 @@ process_g_packet (struct regcache *regcache)
 {
   struct gdbarch *gdbarch = get_regcache_arch (regcache);
   struct remote_state *rs = get_remote_state ();
-  struct remote_arch_state *rsa = get_remote_arch_state ();
+  remote_arch_state *rsa = get_remote_arch_state (gdbarch);
   int i, buf_len;
   char *p;
   char *regs;
@@ -7742,7 +7785,8 @@ static void
 remote_fetch_registers (struct target_ops *ops,
 			struct regcache *regcache, int regnum)
 {
-  struct remote_arch_state *rsa = get_remote_arch_state ();
+  struct gdbarch *gdbarch = get_regcache_arch (regcache);
+  remote_arch_state *rsa = get_remote_arch_state (gdbarch);
   int i;
 
   set_remote_traceframe ();
@@ -7750,7 +7794,7 @@ remote_fetch_registers (struct target_ops *ops,
 
   if (regnum >= 0)
     {
-      struct packet_reg *reg = packet_reg_from_regnum (rsa, regnum);
+      packet_reg *reg = packet_reg_from_regnum (gdbarch, rsa, regnum);
 
       gdb_assert (reg != NULL);
 
@@ -7776,7 +7820,7 @@ remote_fetch_registers (struct target_ops *ops,
 
   fetch_registers_using_g (regcache);
 
-  for (i = 0; i < gdbarch_num_regs (get_regcache_arch (regcache)); i++)
+  for (i = 0; i < gdbarch_num_regs (gdbarch); i++)
     if (!rsa->regs[i].in_g_packet)
       if (!fetch_register_using_p (regcache, &rsa->regs[i]))
 	{
@@ -7792,7 +7836,7 @@ remote_fetch_registers (struct target_ops *ops,
 static void
 remote_prepare_to_store (struct target_ops *self, struct regcache *regcache)
 {
-  struct remote_arch_state *rsa = get_remote_arch_state ();
+  remote_arch_state *rsa = get_remote_arch_state (regcache->arch ());
   int i;
 
   /* Make sure the entire registers array is valid.  */
@@ -7858,7 +7902,7 @@ static void
 store_registers_using_G (const struct regcache *regcache)
 {
   struct remote_state *rs = get_remote_state ();
-  struct remote_arch_state *rsa = get_remote_arch_state ();
+  remote_arch_state *rsa = get_remote_arch_state (regcache->arch ());
   gdb_byte *regs;
   char *p;
 
@@ -7897,7 +7941,8 @@ static void
 remote_store_registers (struct target_ops *ops,
 			struct regcache *regcache, int regnum)
 {
-  struct remote_arch_state *rsa = get_remote_arch_state ();
+  struct gdbarch *gdbarch = regcache->arch ();
+  remote_arch_state *rsa = get_remote_arch_state (gdbarch);
   int i;
 
   set_remote_traceframe ();
@@ -7905,7 +7950,7 @@ remote_store_registers (struct target_ops *ops,
 
   if (regnum >= 0)
     {
-      struct packet_reg *reg = packet_reg_from_regnum (rsa, regnum);
+      packet_reg *reg = packet_reg_from_regnum (gdbarch, rsa, regnum);
 
       gdb_assert (reg != NULL);
 
@@ -7929,7 +7974,7 @@ remote_store_registers (struct target_ops *ops,
 
   store_registers_using_G (regcache);
 
-  for (i = 0; i < gdbarch_num_regs (get_regcache_arch (regcache)); i++)
+  for (i = 0; i < gdbarch_num_regs (gdbarch); i++)
     if (!rsa->regs[i].in_g_packet)
       if (!store_register_using_P (regcache, &rsa->regs[i]))
 	/* See above for why we do not issue an error here.  */
@@ -12697,7 +12742,8 @@ remote_get_trace_status (struct target_ops *self, struct trace_status *ts)
   if (packet_support (PACKET_qTStatus) == PACKET_DISABLE)
     return -1;
 
-  trace_regblock_size = get_remote_arch_state ()->sizeof_g_packet;
+  trace_regblock_size
+    = get_remote_arch_state (target_gdbarch ())->sizeof_g_packet;
 
   putpkt ("qTStatus");