Re: SIG32/SIGTRAP issues

[Daniel Jacobowitz <drow at mvista dot com>]

On Tue, Dec 03, 2002 at 06:56:20PM -0500, Paul Mundt wrote:
> Hi,
> 
> I seem to be running into a bit of an odd problem. When I have a
> threaded application thats shared, everything works fine .. in the event
> that the application is statically linked however, gdb gets a SIG32 at
> pthread_create() time and doesn't track the threads properly.

Funny, no one reports this for months and this is the third report I've
seen in a week...  At the bottom of this message is a workaround.  I'm
not proposing it be committed, since it's obviously pretty gross.  The
real issue is the concept of thread_stratum and core_stratum as
separate from process_stratum.  I don't think it's appropriate - if we
are debugging a core and process at the same time this isn't how it
should work.  This ties in to all the make-targets-a-real-stack thing -
I'm not entirely convinced on that score either.

-- 
Daniel Jacobowitz
MontaVista Software                         Debian GNU/Linux Developer

Not yet submitted upstream.  This requires some serious thinking about. 
If the target stack worked in any logical way, this wouldn't be necessary...
ending up with roughly:
  thread_stratum: thread-db (silent reference to lin-lwp)
  core_stratum: corelow
  exec_stratum: exec
  dummy_stratum: dummy
just makes no sense.

This patch fixes debugging threaded applications which are statically linked
without breaking debugging threaded core files.  It also fixes the PIDs in
generate-core-file'd corefiles.  Mostly.

diff -x '*~' -ur o/gdb-5.2.debian90.cvs20021120/gdb/corelow.c gdb-5.2.debian90.cvs20021120/gdb/corelow.c
--- o/gdb-5.2.debian90.cvs20021120/gdb/corelow.c	2002-09-18 13:23:15.000000000 -0400
+++ gdb-5.2.debian90.cvs20021120/gdb/corelow.c	2002-12-03 14:03:32.000000000 -0500
@@ -350,7 +350,7 @@
   bfd_map_over_sections (core_bfd, add_to_thread_list,
 			 bfd_get_section_by_name (core_bfd, ".reg"));
 
-  if (ontop)
+  if (ontop || 1)
     {
       /* Fetch all registers from core file.  */
       target_fetch_registers (-1);
diff -x '*~' -ur o/gdb-5.2.debian90.cvs20021120/gdb/linux-proc.c gdb-5.2.debian90.cvs20021120/gdb/linux-proc.c
--- o/gdb-5.2.debian90.cvs20021120/gdb/linux-proc.c	2002-12-03 14:13:52.000000000 -0500
+++ gdb-5.2.debian90.cvs20021120/gdb/linux-proc.c	2002-12-03 13:56:34.000000000 -0500
@@ -177,7 +177,7 @@
 #ifdef FILL_FPXREGSET
   gdb_fpxregset_t fpxregs;
 #endif
-  unsigned long merged_pid = ptid_get_tid (ptid) << 16 | ptid_get_pid (ptid);
+  unsigned long merged_pid = ptid_get_tid (ptid) << 16; /*  | ptid_get_pid (ptid); */
 
   fill_gregset (&gregs, -1);
   note_data = (char *) elfcore_write_prstatus (obfd, 
diff -x '*~' -ur o/gdb-5.2.debian90.cvs20021120/gdb/target.c gdb-5.2.debian90.cvs20021120/gdb/target.c
--- o/gdb-5.2.debian90.cvs20021120/gdb/target.c	2002-09-18 13:23:22.000000000 -0400
+++ gdb-5.2.debian90.cvs20021120/gdb/target.c	2002-12-03 14:06:07.000000000 -0500
@@ -1589,6 +1589,7 @@
   dummy_target.to_find_memory_regions = dummy_find_memory_regions;
   dummy_target.to_make_corefile_notes = dummy_make_corefile_notes;
   dummy_target.to_magic = OPS_MAGIC;
+  cleanup_target (&dummy_target);
 }
 
 
diff -x '*~' -ur o/gdb-5.2.debian90.cvs20021120/gdb/thread-db.c gdb-5.2.debian90.cvs20021120/gdb/thread-db.c
--- o/gdb-5.2.debian90.cvs20021120/gdb/thread-db.c	2002-12-03 14:13:50.000000000 -0500
+++ gdb-5.2.debian90.cvs20021120/gdb/thread-db.c	2002-12-03 13:39:54.000000000 -0500
@@ -57,6 +57,31 @@
 /* Non-zero if we're using this module's target vector.  */
 static int using_thread_db;
 
+/* Macros to pass an event to the next target if we should not be handling it
+   here in the thread_stratum.  */
+#define FIND_NEXT_TARGET(METHOD_NAME)			\
+  struct target_ops *next_target = &thread_db_ops;	\
+  while (1)						\
+    {							\
+      next_target = find_target_beneath (next_target);	\
+      if (next_target->METHOD_NAME != NULL)		\
+	break;						\
+    }
+
+#define MAYBE_HAND_DOWN(METHOD_NAME,ARGS)		\
+  if (proc_handle.pid == 0)				\
+    {							\
+      FIND_NEXT_TARGET (METHOD_NAME);			\
+      (*next_target->METHOD_NAME) ARGS;			\
+      return;						\
+    }
+#define MAYBE_HAND_DOWN_RETURN(METHOD_NAME,ARGS)	\
+  if (proc_handle.pid == 0)				\
+    {							\
+      FIND_NEXT_TARGET (METHOD_NAME);			\
+      return (*next_target->METHOD_NAME) ARGS;		\
+    }
+
 /* Non-zero if we have to keep this module's target vector active
    across re-runs.  */
 static int keep_thread_db;
@@ -489,9 +514,7 @@
 {
   td_err_e err;
 
-  /* Don't attempt to use thread_db on targets which can not run
-     (core files).  */
-  if (objfile == NULL || !target_has_execution)
+  if (objfile == NULL)
     {
       /* All symbols have been discarded.  If the thread_db target is
          active, deactivate it now.  */
@@ -515,7 +538,10 @@
   /* Initialize the structure that identifies the child process.  Note
      that at this point there is no guarantee that we actually have a
      child process.  */
-  proc_handle.pid = GET_PID (inferior_ptid);
+  if (target_has_execution)
+    proc_handle.pid = GET_PID (inferior_ptid);
+  else
+    proc_handle.pid = 0;
 
   /* Now attempt to open a connection to the thread library.  */
   err = td_ta_new_p (&proc_handle, &thread_agent);
@@ -758,6 +784,9 @@
   struct cleanup *old_chain = save_inferior_ptid ();
   int xfer;
 
+  MAYBE_HAND_DOWN_RETURN (to_xfer_memory, (memaddr, myaddr, len, write,
+					   attrib, target));
+
   if (is_thread (inferior_ptid))
     {
       /* FIXME: This seems to be necessary to make sure breakpoints
@@ -782,6 +811,8 @@
   gdb_prfpregset_t fpregset;
   td_err_e err;
 
+  MAYBE_HAND_DOWN (to_fetch_registers, (regno));
+
   if (!is_thread (inferior_ptid))
     {
       /* Pass the request to the target beneath us.  */
@@ -819,6 +850,8 @@
   gdb_prfpregset_t fpregset;
   td_err_e err;
 
+  MAYBE_HAND_DOWN (to_store_registers, (regno));
+
   if (!is_thread (inferior_ptid))
     {
       /* Pass the request to the target beneath us.  */
@@ -908,6 +941,8 @@
   td_thrinfo_t ti;
   td_err_e err;
 
+  MAYBE_HAND_DOWN_RETURN (to_thread_alive, (ptid));
+
   if (is_thread (ptid))
     {
       err = td_ta_map_id2thr_p (thread_agent, GET_THREAD (ptid), &th);
@@ -961,6 +996,8 @@
 {
   td_err_e err;
 
+  MAYBE_HAND_DOWN (to_find_new_threads, ());
+
   /* Iterate over all user-space threads to discover new threads.  */
   err = td_ta_thr_iter_p (thread_agent, find_new_threads_callback, NULL,
 			  TD_THR_ANY_STATE, TD_THR_LOWEST_PRIORITY,
@@ -972,6 +1009,8 @@
 static char *
 thread_db_pid_to_str (ptid_t ptid)
 {
+  MAYBE_HAND_DOWN_RETURN (to_pid_to_str, (ptid));
+
   if (is_thread (ptid))
     {
       static char buf[64];