[binutils-gdb] Fix re-runs of a second inferior (PR gdb/25410)

[gdb-buildbot@sergiodj.net]

*** TEST RESULTS FOR COMMIT 53af73bf5e9bad42a76bcc47cdf44d91bbbc4eb7 ***

commit 53af73bf5e9bad42a76bcc47cdf44d91bbbc4eb7
Author:     Pedro Alves <palves@redhat.com>
AuthorDate: Fri Jan 24 18:46:20 2020 +0000
Commit:     Pedro Alves <palves@redhat.com>
CommitDate: Fri Jan 24 18:46:20 2020 +0000

    Fix re-runs of a second inferior (PR gdb/25410)
    
    This fixes a latent bug exposed by the multi-target patch (5b6d1e4fa
    "Multi-target support), and then fixes two other latent bugs exposed
    by fixing that first latent bug.
    
    The symptom described in the bug report is that starting a first
    inferior, then trying to run a second (multi-threaded) inferior twice,
    causes libthread_db to fail to load, along with other erratic
    behavior:
    
     (gdb) run
     Starting program: /tmp/foo
     warning: td_ta_new failed: generic error
    
    Going a bit deeply, I found that if the two inferiors have different
    symbols, we can see that just after inferior 2 exits, we are left with
    inferior 2 selected, which is correct, but the symbols in scope belong
    to inferior 1, which is obviously incorrect...
    
    This problem is that there's a path in
    scoped_restore_current_thread::restore() that switches to no thread
    selected, and switches the current inferior, but leaves the current
    program space as is, resulting in leaving the program space pointing
    to the wrong program space (the one of the other inferior).  This was
    happening after handling TARGET_WAITKIND_NO_RESUMED, which is an event
    that triggers after TARGET_WAITKIND_EXITED for the previous inferior
    exit.  Subsequent symbol lookups find the symbols of the wrong
    inferior.
    
    The fix is to use switch_to_inferior_no_thread in that problem spot.
    This function was recently added along with the multi-target work
    exactly for these situations.
    
    As for testing, this patch adds a new testcase that tests symbol
    printing just after inferior exit, which exercises the root cause of
    the problem more directly.  And then, to cover the use case described
    in the bug too, it also exercises the lithread_db.so mis-loading, by
    using TLS printing as a proxy for being sure that threaded debugging
    was activated sucessfully.  The testcase fails without the fix like
    this, for the "print symbol just after exit" bits:
    
     ...
     [Inferior 1 (process 8719) exited normally]
     (gdb) PASS: gdb.multi/multi-re-run.exp: re_run_inf=1: iter=1: continue until exit
     print re_run_var_1
     No symbol "re_run_var_1" in current context.
     (gdb) FAIL: gdb.multi/multi-re-run.exp: re_run_inf=1: iter=1: print re_run_var_1
     ...
    
    And like this for the "libthread_db.so loading" bits:
    
     (gdb) run
     Starting program: /home/pedro/gdb/binutils-gdb/build/gdb/testsuite/outputs/gdb.multi/multi-re-run/multi-re-run
     warning: td_ta_new failed: generic error
     [New LWP 27001]
    
     Thread 1.1 "multi-re-run" hit Breakpoint 3, all_started () at /home/pedro/gdb/binutils-gdb/build/../src/gdb/testsuite/gdb.multi/multi-re-run.c:44
     44      }
     (gdb) PASS: gdb.multi/multi-re-run.exp: re_run_inf=1: iter=2: running to all_started in runto
     print tls_var
     Cannot find thread-local storage for LWP 27000, executable file /home/pedro/gdb/binutils-gdb/build/gdb/testsuite/outputs/gdb.multi/multi-re-run/multi-re-run:
     Cannot find thread-local variables on this target
     (gdb) FAIL: gdb.multi/multi-re-run.exp: re_run_inf=1: iter=2: print tls_var
    
    
    As mentioned, that fix above goes on to expose a couple other latent
    bugs.  This commit fixes those as well.
    
    The first latent bug exposed is in
    infrun.c:handle_vfork_child_exec_or_exit.  The current code is leaving
    inf->pspace == NULL while calling clone_program_space.  The idea was
    to make it so that the breakpoints module doesn't use this inferior's
    pspace to set breakpoints.  With that, any
    scoped_restore_current_thread use from within clone_program_space
    tries to restore a NULL program space, which hits an assertion:
    
     Attaching after Thread 0x7ffff74b8700 (LWP 27276) vfork to child process 27277]
     [New inferior 2 (process 27277)]
     [Thread debugging using libthread_db enabled]
     Using host libthread_db library "/lib64/libthread_db.so.1".
     /home/pedro/gdb/binutils-gdb/build/../src/gdb/progspace.c:243: internal-error: void set_current_program_space(program_space*): Assertion `pspace != NULL' faile
     d.
     A problem internal to GDB has been detected,
     further debugging may prove unreliable.
     Quit this debugging session? (y or n) FAIL: gdb.threads/vfork-follow-child-exit.exp: detach-on-fork=off: continue (GDB internal error)
    
    That NULL pspace idea was legitimate, but it's no longer necessary,
    since commit b2e586e850db ("Defer breakpoint reset when cloning
    progspace for fork child").  So the fix is to just set the inferior's
    program space earlier.
    
    
    The other latent bug exposed is in exec.c.  When exec_close is called
    from the program_space destructor, it is purposedly called with a
    current program space that is not the current inferior's program
    space.  The problem is that the multi-target work added some code to
    remove_target_sections that loops over all inferiors, and uses
    scoped_restore_current_thread to save/restore the previous
    thread/inferior/frame state.  This makes it so that exec_close returns
    with the current program space set to the current inferior's program
    space, which is exactly what we did not want.  Then the program_space
    destructor continues into free_all_objfiles, but it is now running
    that method on the wrong program space, resulting in:
    
     Reading symbols from /home/pedro/gdb/binutils-gdb/build/gdb/testsuite/outputs/gdb.threads/fork-plus-threads/fork-plus-threads...
     Reading symbols from /usr/lib/debug/usr/lib64/libpthread-2.26.so.debug...
     Reading symbols from /usr/lib/debug/usr/lib64/libm-2.26.so.debug...
     Reading symbols from /usr/lib/debug/usr/lib64/libc-2.26.so.debug...
     Reading symbols from /usr/lib/debug/usr/lib64/ld-2.26.so.debug...
     [Inferior 3 (process 9583) exited normally]
     /home/pedro/gdb/binutils-gdb/build/../src/gdb/progspace.c:170: internal-error: void program_space::free_all_objfiles(): Assertion `so->objfile == NULL' failed.
     A problem internal to GDB has been detected,
     further debugging may prove unreliable.
     Quit this debugging session? (y or n) FAIL: gdb.threads/fork-plus-threads.exp: detach-on-fork=off: inferior 1 exited (GDB internal error)
    
    The fix is to use scoped_restore_current_pspace_and_thread instead of
    scoped_restore_current_thread.
    
    gdb/ChangeLog:
    2020-01-24  Pedro Alves  <palves@redhat.com>
    
            PR gdb/25410
            * thread.c (scoped_restore_current_thread::restore): Use
            switch_to_inferior_no_thread.
            * exec.c: Include "progspace-and-thread.h".
            (add_target_sections, remove_target_sections):
            scoped_restore_current_pspace_and_thread instead of
            scoped_restore_current_thread.
            * infrun.c (handle_vfork_child_exec_or_exit): Assign the pspace
            and aspace to the inferior before calling clone_program_space.
            Remove stale comment.
    
    gdb/testsuite/ChangeLog:
    2020-01-24  Pedro Alves  <palves@redhat.com>
    
            PR gdb/25410
            * gdb.multi/multi-re-run-1.c: New.
            * gdb.multi/multi-re-run-2.c: New.
            * gdb.multi/multi-re-run.exp: New.

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 3d166f0640..16d16ef6dc 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,16 @@
+2020-01-24  Pedro Alves  <palves@redhat.com>
+
+	PR gdb/25410
+	* thread.c (scoped_restore_current_thread::restore): Use
+	switch_to_inferior_no_thread.
+	* exec.c: Include "progspace-and-thread.h".
+	(add_target_sections, remove_target_sections):
+	scoped_restore_current_pspace_and_thread instead of
+	scoped_restore_current_thread.
+	* infrun.c (handle_vfork_child_exec_or_exit): Assign the pspace
+	and aspace to the inferior before calling clone_program_space.
+	Remove stale comment.
+
 2020-01-24  Christian Biesinger  <cbiesinger@google.com>
 
 	* arm-nbsd-nat.c (arm_nbsd_nat_target::fetch_registers): Rename to...
diff --git a/gdb/exec.c b/gdb/exec.c
index eb07b51dda..2506e84157 100644
--- a/gdb/exec.c
+++ b/gdb/exec.c
@@ -33,6 +33,7 @@
 #include "arch-utils.h"
 #include "gdbthread.h"
 #include "progspace.h"
+#include "progspace-and-thread.h"
 #include "gdb_bfd.h"
 #include "gcore.h"
 #include "source.h"
@@ -547,7 +548,7 @@ add_target_sections (void *owner,
 	  table->sections[space + i].owner = owner;
 	}
 
-      scoped_restore_current_thread restore_thread;
+      scoped_restore_current_pspace_and_thread restore_pspace_thread;
       program_space *curr_pspace = current_program_space;
 
       /* If these are the first file sections we can provide memory
@@ -645,7 +646,7 @@ remove_target_sections (void *owner)
 	 inferior sharing the program space.  */
       if (old_count + (dest - src) == 0)
 	{
-	  scoped_restore_current_thread restore_thread;
+	  scoped_restore_current_pspace_and_thread restore_pspace_thread;
 	  program_space *curr_pspace = current_program_space;
 
 	  for (inferior *inf : all_inferiors ())
diff --git a/gdb/infrun.c b/gdb/infrun.c
index 9c4a07daba..22de42c2ae 100644
--- a/gdb/infrun.c
+++ b/gdb/infrun.c
@@ -1020,8 +1020,6 @@ handle_vfork_child_exec_or_exit (int exec)
 	}
       else
 	{
-	  struct program_space *pspace;
-
 	  /* If this is a vfork child exiting, then the pspace and
 	     aspaces were shared with the parent.  Since we're
 	     reporting the process exit, we'll be mourning all that is
@@ -1037,18 +1035,12 @@ handle_vfork_child_exec_or_exit (int exec)
 	  scoped_restore restore_ptid
 	    = make_scoped_restore (&inferior_ptid, null_ptid);
 
-	  /* This inferior is dead, so avoid giving the breakpoints
-	     module the option to write through to it (cloning a
-	     program space resets breakpoints).  */
-	  inf->aspace = NULL;
-	  inf->pspace = NULL;
-	  pspace = new program_space (maybe_new_address_space ());
-	  set_current_program_space (pspace);
+	  inf->pspace = new program_space (maybe_new_address_space ());
+	  inf->aspace = inf->pspace->aspace;
+	  set_current_program_space (inf->pspace);
 	  inf->removable = 1;
 	  inf->symfile_flags = SYMFILE_NO_READ;
-	  clone_program_space (pspace, vfork_parent->pspace);
-	  inf->pspace = pspace;
-	  inf->aspace = pspace->aspace;
+	  clone_program_space (inf->pspace, vfork_parent->pspace);
 
 	  resume_parent = vfork_parent->pid;
 	}
diff --git a/gdb/testsuite/ChangeLog b/gdb/testsuite/ChangeLog
index 3a97848060..81500c21ae 100644
--- a/gdb/testsuite/ChangeLog
+++ b/gdb/testsuite/ChangeLog
@@ -1,3 +1,10 @@
+2020-01-24  Pedro Alves  <palves@redhat.com>
+
+	PR gdb/25410
+	* gdb.multi/multi-re-run-1.c: New.
+	* gdb.multi/multi-re-run-2.c: New.
+	* gdb.multi/multi-re-run.exp: New.
+
 2020-01-24  Andrew Burgess  <andrew.burgess@embecosm.com>
 
 	PR gdb/23718
diff --git a/gdb/testsuite/gdb.multi/multi-re-run-1.c b/gdb/testsuite/gdb.multi/multi-re-run-1.c
new file mode 100644
index 0000000000..91b0dbce30
--- /dev/null
+++ b/gdb/testsuite/gdb.multi/multi-re-run-1.c
@@ -0,0 +1,61 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+   Copyright 2020 Free Software Foundation, Inc.
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+#include <stdlib.h>
+#include <stdio.h>
+#include <unistd.h>
+#include <limits.h>
+#include <string.h>
+#include <pthread.h>
+
+int re_run_var_1 = 1;
+
+#define NUM_THREADS 1
+
+__thread int tls_var = 1;
+
+static pthread_barrier_t barrier;
+
+static void *
+thread_start (void *arg)
+{
+  pthread_barrier_wait (&barrier);
+
+  while (1)
+    sleep (1);
+  return NULL;
+}
+
+static void
+all_started (void)
+{
+}
+
+int
+main (int argc, char ** argv)
+{
+  pthread_t thread;
+  int len;
+
+  pthread_barrier_init (&barrier, NULL, NUM_THREADS + 1);
+  pthread_create (&thread, NULL, thread_start, NULL);
+
+  pthread_barrier_wait (&barrier);
+  all_started ();
+
+  return 0;
+}
diff --git a/gdb/testsuite/gdb.multi/multi-re-run-2.c b/gdb/testsuite/gdb.multi/multi-re-run-2.c
new file mode 100644
index 0000000000..6925e0cb2d
--- /dev/null
+++ b/gdb/testsuite/gdb.multi/multi-re-run-2.c
@@ -0,0 +1,61 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+   Copyright 2020 Free Software Foundation, Inc.
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+#include <stdlib.h>
+#include <stdio.h>
+#include <unistd.h>
+#include <limits.h>
+#include <string.h>
+#include <pthread.h>
+
+int re_run_var_2 = 2;
+
+#define NUM_THREADS 1
+
+__thread int tls_var = 1;
+
+static pthread_barrier_t barrier;
+
+static void *
+thread_start (void *arg)
+{
+  pthread_barrier_wait (&barrier);
+
+  while (1)
+    sleep (1);
+  return NULL;
+}
+
+static void
+all_started (void)
+{
+}
+
+int
+main (int argc, char ** argv)
+{
+  pthread_t thread;
+  int len;
+
+  pthread_barrier_init (&barrier, NULL, NUM_THREADS + 1);
+  pthread_create (&thread, NULL, thread_start, NULL);
+
+  pthread_barrier_wait (&barrier);
+  all_started ();
+
+  return 0;
+}
diff --git a/gdb/testsuite/gdb.multi/multi-re-run.exp b/gdb/testsuite/gdb.multi/multi-re-run.exp
new file mode 100644
index 0000000000..93cd709b5c
--- /dev/null
+++ b/gdb/testsuite/gdb.multi/multi-re-run.exp
@@ -0,0 +1,115 @@
+# Copyright 2020 Free Software Foundation, Inc.
+
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+# Test loading two inferiors into GDB, and running one of them twice
+# in a row.  GDB used to have a bug that made it so that after an
+# inferior exit, the current program space was left pointing to the
+# wrong inferior's pspace, causing subsequent symbol lookups to
+# misbehave, including failing to load libthread_db.so.  See PR
+# gdb/25410.
+
+# Build two executables, with different symbols.
+
+set exec1 "multi-re-run-1"
+set srcfile1 multi-re-run-1.c
+set binfile1 [standard_output_file ${exec1}]
+
+set exec2 "multi-re-run-2"
+set srcfile2 multi-re-run-2.c
+set binfile2 [standard_output_file ${exec2}]
+
+with_test_prefix "exec1" {
+    if { [prepare_for_testing "failed to prepare" ${exec1} "${srcfile1}" \
+	      [list pthreads debug]] } {
+	return -1
+    }
+}
+
+with_test_prefix "exec2" {
+    if { [prepare_for_testing "failed to prepare" ${exec2} "${srcfile2}" \
+	      [list pthreads debug]] } {
+	return -1
+    }
+}
+
+# Start two inferiors, leave one stopped, and run the other a couple
+# times.  RE_RUN_INF is the inferior that is re-run.
+
+proc test_re_run {re_run_inf} {
+    global binfile1 binfile2
+    global inferior_exited_re
+    global gdb_prompt
+
+    clean_restart ${binfile1}
+
+    delete_breakpoints
+
+    # Start another inferior.
+    gdb_test "add-inferior" "Added inferior 2.*" \
+	"add empty inferior 2"
+    gdb_test "inferior 2" "Switching to inferior 2.*" \
+	"switch to inferior 2"
+    gdb_load ${binfile2}
+
+    if {$re_run_inf == 1} {
+	set steady_inf 2
+    } else {
+	set steady_inf 1
+    }
+
+    gdb_test "inferior $steady_inf" "Switching to inferior $steady_inf.*" \
+	"switch to steady inferior"
+
+    # Run the steady inferior to a breakpoint, and let it stay stopped
+    # there.
+    if ![runto all_started message] then {
+	untested "setup failed"
+	return 0
+    }
+
+    gdb_test "inferior $re_run_inf" "Switching to inferior $re_run_inf.*" \
+	"switch to re-run inferior"
+
+    # Now run the RE_RUN_INF inferior a couple times.  GDB used to
+    # have a bug that caused the second run to fail to load
+    # libthread_db.so.
+    foreach_with_prefix iter {1 2} {
+	delete_breakpoints
+
+	if ![runto all_started message] {
+	    return 0
+	}
+
+	# If a thread_stratum target fails to load, then TLS debugging
+	# fails too.
+	gdb_test "print tls_var" " = 1"
+
+	gdb_continue_to_end "" continue 1
+
+	# In the original bug, after an inferior exit, GDB would leave
+	# the current program space pointing to the wrong inferior's
+	# pspace, and thus the wrong symbols were visible.
+	if {$re_run_inf == 1} {
+	    gdb_test "print re_run_var_1" " = 1"
+	} else {
+	    gdb_test "print re_run_var_2" " = 2"
+	}
+    }
+}
+
+# For completeness, test re-running either inferior 1 or inferior 2.
+foreach_with_prefix re_run_inf {1 2} {
+    test_re_run $re_run_inf
+}
diff --git a/gdb/thread.c b/gdb/thread.c
index 001fdd42c5..302a49e984 100644
--- a/gdb/thread.c
+++ b/gdb/thread.c
@@ -1429,10 +1429,7 @@ scoped_restore_current_thread::restore ()
       && m_inf->pid != 0)
     switch_to_thread (m_thread);
   else
-    {
-      switch_to_no_thread ();
-      set_current_inferior (m_inf);
-    }
+    switch_to_inferior_no_thread (m_inf);
 
   /* The running state of the originally selected thread may have
      changed, so we have to recheck it here.  */