PR 20569, segv in follow_exec

The following testcases make GDB crash whenever an invalid sysroot is
provided, when GDB is unable to find a valid path to the symbol file:

 gdb.base/catch-syscall.exp
 gdb.base/execl-update-breakpoints.exp
 gdb.base/foll-exec-mode.exp
 gdb.base/foll-exec.exp
 gdb.base/foll-vfork.exp
 gdb.base/pie-execl.exp
 gdb.multi/bkpt-multi-exec.exp
 gdb.python/py-finish-breakpoint.exp
 gdb.threads/execl.exp
 gdb.threads/non-ldr-exc-1.exp
 gdb.threads/non-ldr-exc-2.exp
 gdb.threads/non-ldr-exc-3.exp
 gdb.threads/non-ldr-exc-4.exp
 gdb.threads/thread-execl.exp

The immediate cause of the segv is that follow_exec is passing a NULL
argument (the result of exec_file_find) to strlen.

However, the problem is deeper than that: follow_exec simply isn't
prepared for the case where sysroot translation fails to locate the
new executable.  Actually all callers of exec_file_find have bugs due
to confusion between host and target pathnames.  This commit attempts
to fix all that.

In terms of the testcases that were formerly segv'ing, GDB now prints
a warning but continues execution of the new program, so that the
tests now mostly FAIL instead.  You could argue the FAILs are due to a
legitimate problem with the test environment setting up the sysroot
translation incorrectly.

A new representative test is added which exercises the ne wwarning
code path even with native testing.

Tested on x86_64 Fedora 23, native and gdbserver.

gdb/ChangeLog:
2016-10-25  Sandra Loosemore  <sandra@codesourcery.com>
	    Luis Machado  <lgustavo@codesourcery.com>
	    Pedro Alves  <palves@redhat.com>

	PR gdb/20569
	* exceptions.c (exception_print_same): Moved here from exec.c.
	* exceptions.h (exception_print_same): Declare.
	* exec.h: Include "symfile-add-flags.h".
	(try_open_exec_file): New declaration.
	* exec.c (exception_print_same): Moved to exceptions.c.
	(try_open_exec_file): New function.
	(exec_file_locate_attach): Rename exec_file and full_exec_path
	variables to avoid confusion between target and host pathnames.
	Move pathname processing logic to exec_file_find.  Do not return
	early if pathname lookup fails; Call try_open_exec_file.
	* infrun.c (follow_exec): Split and rename execd_pathname variable
	to avoid confusion between target and host pathnames.  Warn if
	pathname lookup fails.  Pass target pathname to
	target_follow_exec, not hostpathname.  Call try_open_exec_file.
	* main.c (symbol_file_add_main_adapter): New function.
	(captured_main_1): Use it.
	* solib-svr4.c (open_symbol_file_object): Adjust to pass
	symfile_add_flags to symbol_file_add_main.
	* solib.c (exec_file_find): Incorporate fallback logic for relative
	pathnames formerly in exec_file_locate_attach.
	* symfile.c (symbol_file_add_main, symbol_file_add_main_1):
	Replace 'from_tty' parameter with a symfile_add_file.
	(symbol_file_command): Adjust to pass symfile_add_flags to
	symbol_file_add_main.
	* symfile.h (symbol_file_add_main): Replace 'from_tty' parameter
	with a symfile_add_file.

gdb/testsuite/ChangeLog:
2016-10-25  Luis Machado  <lgustavo@codesourcery.com>

	* gdb.base/exec-invalid-sysroot.exp: New file.

14 files changed, 275 insertions, 119 deletions

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 45e29cc3011..768d166cd5e 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,35 @@
+2016-10-25  Sandra Loosemore  <sandra@codesourcery.com>
+	    Luis Machado  <lgustavo@codesourcery.com>
+	    Pedro Alves  <palves@redhat.com>
+
+	PR gdb/20569
+	* exceptions.c (exception_print_same): Moved here from exec.c.
+	* exceptions.h (exception_print_same): Declare.
+	* exec.h: Include "symfile-add-flags.h".
+	(try_open_exec_file): New declaration.
+	* exec.c (exception_print_same): Moved to exceptions.c.
+	(try_open_exec_file): New function.
+	(exec_file_locate_attach): Rename exec_file and full_exec_path
+	variables to avoid confusion between target and host pathnames.
+	Move pathname processing logic to exec_file_find.  Do not return
+	early if pathname lookup fails; Call try_open_exec_file.
+	* infrun.c (follow_exec): Split and rename execd_pathname variable
+	to avoid confusion between target and host pathnames.  Warn if
+	pathname lookup fails.  Pass target pathname to
+	target_follow_exec, not hostpathname.  Call try_open_exec_file.
+	* main.c (symbol_file_add_main_adapter): New function.
+	(captured_main_1): Use it.
+	* solib-svr4.c (open_symbol_file_object): Adjust to pass
+	symfile_add_flags to symbol_file_add_main.
+	* solib.c (exec_file_find): Incorporate fallback logic for relative
+	pathnames formerly in exec_file_locate_attach.
+	* symfile.c (symbol_file_add_main, symbol_file_add_main_1):
+	Replace 'from_tty' parameter with a symfile_add_file.
+	(symbol_file_command): Adjust to pass symfile_add_flags to
+	symbol_file_add_main.
+	* symfile.h (symbol_file_add_main): Replace 'from_tty' parameter
+	with a symfile_add_file.
+
 2016-10-26  Pedro Alves  <palves@redhat.com>
 
 	* coffread.c (coff_symfile_read): Use symfile_add_flags.
diff --git a/gdb/exceptions.c b/gdb/exceptions.c
index 9a10f665286..99199382bb5 100644
--- a/gdb/exceptions.c
+++ b/gdb/exceptions.c
@@ -256,3 +256,21 @@ catch_errors (catch_errors_ftype *func, void *func_args, char *errstring,
     return 0;
   return val;
 }
+
+/* See exceptions.h.  */
+
+int
+exception_print_same (struct gdb_exception e1, struct gdb_exception e2)
+{
+  const char *msg1 = e1.message;
+  const char *msg2 = e2.message;
+
+  if (msg1 == NULL)
+    msg1 = "";
+  if (msg2 == NULL)
+    msg2 = "";
+
+  return (e1.reason == e2.reason
+	  && e1.error == e2.error
+	  && strcmp (msg1, msg2) == 0);
+}
diff --git a/gdb/exceptions.h b/gdb/exceptions.h
index 5711c1a35e1..a2d39d7d4a6 100644
--- a/gdb/exceptions.h
+++ b/gdb/exceptions.h
@@ -88,4 +88,7 @@ extern int catch_exceptions_with_msg (struct ui_out *uiout,
 typedef int (catch_errors_ftype) (void *);
 extern int catch_errors (catch_errors_ftype *, void *, char *, return_mask);
 
+/* Compare two exception objects for print equality.  */
+extern int exception_print_same (struct gdb_exception e1,
+				 struct gdb_exception e2);
 #endif
diff --git a/gdb/exec.c b/gdb/exec.c
index 6e2a296d2e6..eeca005b39f 100644
--- a/gdb/exec.c
+++ b/gdb/exec.c
@@ -136,73 +136,16 @@ exec_file_clear (int from_tty)
     printf_unfiltered (_("No executable file now.\n"));
 }
 
-/* Returns non-zero if exceptions E1 and E2 are equal.  Returns zero
-   otherwise.  */
-
-static int
-exception_print_same (struct gdb_exception e1, struct gdb_exception e2)
-{
-  const char *msg1 = e1.message;
-  const char *msg2 = e2.message;
-
-  if (msg1 == NULL)
-    msg1 = "";
-  if (msg2 == NULL)
-    msg2 = "";
-
-  return (e1.reason == e2.reason
-	  && e1.error == e2.error
-	  && strcmp (msg1, msg2) == 0);
-}
-
-/* See gdbcore.h.  */
+/* See exec.h.  */
 
 void
-exec_file_locate_attach (int pid, int defer_bp_reset, int from_tty)
+try_open_exec_file (const char *exec_file_host, struct inferior *inf,
+		    symfile_add_flags add_flags)
 {
-  char *exec_file, *full_exec_path = NULL;
   struct cleanup *old_chain;
   struct gdb_exception prev_err = exception_none;
 
-  /* Do nothing if we already have an executable filename.  */
-  exec_file = (char *) get_exec_file (0);
-  if (exec_file != NULL)
-    return;
-
-  /* Try to determine a filename from the process itself.  */
-  exec_file = target_pid_to_exec_file (pid);
-  if (exec_file == NULL)
-    {
-      warning (_("No executable has been specified and target does not "
-		 "support\n"
-		 "determining executable automatically.  "
-		 "Try using the \"file\" command."));
-      return;
-    }
-
-  /* If gdb_sysroot is not empty and the discovered filename
-     is absolute then prefix the filename with gdb_sysroot.  */
-  if (*gdb_sysroot != '\0' && IS_ABSOLUTE_PATH (exec_file))
-    {
-      full_exec_path = exec_file_find (exec_file, NULL);
-      if (full_exec_path == NULL)
-	return;
-    }
-  else
-    {
-      /* It's possible we don't have a full path, but rather just a
-	 filename.  Some targets, such as HP-UX, don't provide the
-	 full path, sigh.
-
-	 Attempt to qualify the filename against the source path.
-	 (If that fails, we'll just fall back on the original
-	 filename.  Not much more we can do...)  */
-      if (!source_full_path_of (exec_file, &full_exec_path))
-	full_exec_path = xstrdup (exec_file);
-    }
-
-  old_chain = make_cleanup (xfree, full_exec_path);
-  make_cleanup (free_current_contents, &prev_err.message);
+  old_chain = make_cleanup (free_current_contents, &prev_err.message);
 
   /* exec_file_attach and symbol_file_add_main may throw an error if the file
      cannot be opened either locally or remotely.
@@ -217,7 +160,9 @@ exec_file_locate_attach (int pid, int defer_bp_reset, int from_tty)
      errors/exceptions in the following code.  */
   TRY
     {
-      exec_file_attach (full_exec_path, from_tty);
+      /* We must do this step even if exec_file_host is NULL, so that
+	 exec_file_attach will clear state.  */
+      exec_file_attach (exec_file_host, add_flags & SYMFILE_VERBOSE);
     }
   CATCH (err, RETURN_MASK_ERROR)
     {
@@ -232,20 +177,58 @@ exec_file_locate_attach (int pid, int defer_bp_reset, int from_tty)
     }
   END_CATCH
 
-  TRY
+  if (exec_file_host != NULL)
     {
-      if (defer_bp_reset)
-	current_inferior ()->symfile_flags |= SYMFILE_DEFER_BP_RESET;
-      symbol_file_add_main (full_exec_path, from_tty);
+      TRY
+	{
+	  symbol_file_add_main (exec_file_host, add_flags);
+	}
+      CATCH (err, RETURN_MASK_ERROR)
+	{
+	  if (!exception_print_same (prev_err, err))
+	    warning ("%s", err.message);
+	}
+      END_CATCH
     }
-  CATCH (err, RETURN_MASK_ERROR)
+
+  do_cleanups (old_chain);
+}
+
+/* See gdbcore.h.  */
+
+void
+exec_file_locate_attach (int pid, int defer_bp_reset, int from_tty)
+{
+  char *exec_file_target, *exec_file_host;
+  struct cleanup *old_chain;
+  symfile_add_flags add_flags = 0;
+
+  /* Do nothing if we already have an executable filename.  */
+  if (get_exec_file (0) != NULL)
+    return;
+
+  /* Try to determine a filename from the process itself.  */
+  exec_file_target = target_pid_to_exec_file (pid);
+  if (exec_file_target == NULL)
     {
-      if (!exception_print_same (prev_err, err))
-	warning ("%s", err.message);
+      warning (_("No executable has been specified and target does not "
+		 "support\n"
+		 "determining executable automatically.  "
+		 "Try using the \"file\" command."));
+      return;
     }
-  END_CATCH
-  current_inferior ()->symfile_flags &= ~SYMFILE_DEFER_BP_RESET;
 
+  exec_file_host = exec_file_find (exec_file_target, NULL);
+  old_chain = make_cleanup (xfree, exec_file_host);
+
+  if (defer_bp_reset)
+    add_flags |= SYMFILE_DEFER_BP_RESET;
+
+  if (from_tty)
+    add_flags |= SYMFILE_VERBOSE;
+
+  /* Attempt to open the exec file.  */
+  try_open_exec_file (exec_file_host, current_inferior (), add_flags);
   do_cleanups (old_chain);
 }
 
diff --git a/gdb/exec.h b/gdb/exec.h
index 4044cb71b8b..f50e9eadb3f 100644
--- a/gdb/exec.h
+++ b/gdb/exec.h
@@ -23,6 +23,7 @@
 #include "target.h"
 #include "progspace.h"
 #include "memrange.h"
+#include "symfile-add-flags.h"
 
 struct target_section;
 struct target_ops;
@@ -113,4 +114,11 @@ extern void print_section_info (struct target_section_table *table,
 
 extern void exec_close (void);
 
+/* Helper function that attempts to open the symbol file at EXEC_FILE_HOST.
+   If successful, it proceeds to add the symbol file as the main symbol file.
+
+   ADD_FLAGS is passed on to the function adding the symbol file.  */
+extern void try_open_exec_file (const char *exec_file_host,
+				struct inferior *inf,
+				symfile_add_flags add_flags);
 #endif
diff --git a/gdb/inferior.c b/gdb/inferior.c
index 250603c85cc..92a18d66274 100644
--- a/gdb/inferior.c
+++ b/gdb/inferior.c
@@ -854,8 +854,12 @@ add_inferior_command (char *args, int from_tty)
   int i, copies = 1;
   char *exec = NULL;
   char **argv;
+  symfile_add_flags add_flags = 0;
   struct cleanup *old_chain = make_cleanup (null_cleanup, NULL);
 
+  if (from_tty)
+    add_flags |= SYMFILE_VERBOSE;
+
   if (args)
     {
       argv = gdb_buildargv (args);
@@ -903,7 +907,7 @@ add_inferior_command (char *args, int from_tty)
 	  switch_to_thread (null_ptid);
 
 	  exec_file_attach (exec, from_tty);
-	  symbol_file_add_main (exec, from_tty);
+	  symbol_file_add_main (exec, add_flags);
 	}
     }
 
diff --git a/gdb/infrun.c b/gdb/infrun.c
index 5e624729d38..b10aa03b669 100644
--- a/gdb/infrun.c
+++ b/gdb/infrun.c
@@ -1077,15 +1077,17 @@ show_follow_exec_mode_string (struct ui_file *file, int from_tty,
   fprintf_filtered (file, _("Follow exec mode is \"%s\".\n"),  value);
 }
 
-/* EXECD_PATHNAME is assumed to be non-NULL.  */
+/* EXEC_FILE_TARGET is assumed to be non-NULL.  */
 
 static void
-follow_exec (ptid_t ptid, char *execd_pathname)
+follow_exec (ptid_t ptid, char *exec_file_target)
 {
   struct thread_info *th, *tmp;
   struct inferior *inf = current_inferior ();
   int pid = ptid_get_pid (ptid);
   ptid_t process_ptid;
+  char *exec_file_host;
+  struct cleanup *old_chain;
 
   /* This is an exec event that we actually wish to pay attention to.
      Refresh our symbol table to the newly exec'd program, remove any
@@ -1155,7 +1157,7 @@ follow_exec (ptid_t ptid, char *execd_pathname)
   process_ptid = pid_to_ptid (pid);
   printf_unfiltered (_("%s is executing new program: %s\n"),
 		     target_pid_to_str (process_ptid),
-		     execd_pathname);
+		     exec_file_target);
 
   /* We've followed the inferior through an exec.  Therefore, the
      inferior has essentially been killed & reborn.  */
@@ -1164,14 +1166,17 @@ follow_exec (ptid_t ptid, char *execd_pathname)
 
   breakpoint_init_inferior (inf_execd);
 
-  if (*gdb_sysroot != '\0')
-    {
-      char *name = exec_file_find (execd_pathname, NULL);
+  exec_file_host = exec_file_find (exec_file_target, NULL);
+  old_chain = make_cleanup (xfree, exec_file_host);
 
-      execd_pathname = (char *) alloca (strlen (name) + 1);
-      strcpy (execd_pathname, name);
-      xfree (name);
-    }
+  /* If we were unable to map the executable target pathname onto a host
+     pathname, tell the user that.  Otherwise GDB's subsequent behavior
+     is confusing.  Maybe it would even be better to stop at this point
+     so that the user can specify a file manually before continuing.  */
+  if (exec_file_host == NULL)
+    warning (_("Could not load symbols for executable %s.\n"
+	       "Do you need \"set sysroot\"?"),
+	     exec_file_target);
 
   /* Reset the shared library package.  This ensures that we get a
      shlib event when the child reaches "_start", at which point the
@@ -1193,7 +1198,7 @@ follow_exec (ptid_t ptid, char *execd_pathname)
 
       inf = add_inferior_with_spaces ();
       inf->pid = pid;
-      target_follow_exec (inf, execd_pathname);
+      target_follow_exec (inf, exec_file_target);
 
       set_current_inferior (inf);
       set_current_program_space (inf->pspace);
@@ -1212,21 +1217,14 @@ follow_exec (ptid_t ptid, char *execd_pathname)
 
   gdb_assert (current_program_space == inf->pspace);
 
-  /* That a.out is now the one to use.  */
-  exec_file_attach (execd_pathname, 0);
+  /* Attempt to open the exec file.  SYMFILE_DEFER_BP_RESET is used
+     because the proper displacement for a PIE (Position Independent
+     Executable) main symbol file will only be computed by
+     solib_create_inferior_hook below.  breakpoint_re_set would fail
+     to insert the breakpoints with the zero displacement.  */
+  try_open_exec_file (exec_file_host, inf, SYMFILE_DEFER_BP_RESET);
 
-  /* SYMFILE_DEFER_BP_RESET is used as the proper displacement for PIE
-     (Position Independent Executable) main symbol file will get applied by
-     solib_create_inferior_hook below.  breakpoint_re_set would fail to insert
-     the breakpoints with the zero displacement.  */
-
-  symbol_file_add (execd_pathname,
-		   (inf->symfile_flags
-		    | SYMFILE_MAINLINE | SYMFILE_DEFER_BP_RESET),
-		   NULL, 0);
-
-  if ((inf->symfile_flags & SYMFILE_NO_READ) == 0)
-    set_initial_language ();
+  do_cleanups (old_chain);
 
   /* If the target can specify a description, read it.  Must do this
      after flipping to the new executable (because the target supplied
diff --git a/gdb/main.c b/gdb/main.c
index 23852e2d470..ca6a81e804a 100644
--- a/gdb/main.c
+++ b/gdb/main.c
@@ -413,6 +413,20 @@ catch_command_errors_const (catch_command_errors_const_ftype *command,
   return 1;
 }
 
+/* Adapter for symbol_file_add_main that translates 'from_tty' to a
+   symfile_add_flags.  */
+
+static void
+symbol_file_add_main_adapter (const char *arg, int from_tty)
+{
+  symfile_add_flags add_flags = 0;
+
+  if (from_tty)
+    add_flags |= SYMFILE_VERBOSE;
+
+  symbol_file_add_main (arg, add_flags);
+}
+
 /* Type of this option.  */
 enum cmdarg_kind
 {
@@ -1029,7 +1043,7 @@ captured_main_1 (struct captured_main_args *context)
          catch_command_errors returns non-zero on success!  */
       if (catch_command_errors_const (exec_file_attach, execarg,
 				      !batch_flag))
-	catch_command_errors_const (symbol_file_add_main, symarg,
+	catch_command_errors_const (symbol_file_add_main_adapter, symarg,
 				    !batch_flag);
     }
   else
@@ -1038,7 +1052,7 @@ captured_main_1 (struct captured_main_args *context)
 	catch_command_errors_const (exec_file_attach, execarg,
 				    !batch_flag);
       if (symarg != NULL)
-	catch_command_errors_const (symbol_file_add_main, symarg,
+	catch_command_errors_const (symbol_file_add_main_adapter, symarg,
 				    !batch_flag);
     }
 
diff --git a/gdb/solib-svr4.c b/gdb/solib-svr4.c
index 258d7dc49ea..0e18292561a 100644
--- a/gdb/solib-svr4.c
+++ b/gdb/solib-svr4.c
@@ -1022,6 +1022,10 @@ open_symbol_file_object (void *from_ttyp)
   gdb_byte *l_name_buf = (gdb_byte *) xmalloc (l_name_size);
   struct cleanup *cleanups = make_cleanup (xfree, l_name_buf);
   struct svr4_info *info = get_svr4_info ();
+  symfile_add_flags add_flags = 0;
+
+  if (from_tty)
+    add_flags |= SYMFILE_VERBOSE;
 
   if (symfile_objfile)
     if (!query (_("Attempt to reload symbols from process? ")))
@@ -1071,7 +1075,7 @@ open_symbol_file_object (void *from_ttyp)
     }
 
   /* Have a pathname: read the symbol file.  */
-  symbol_file_add_main (filename, from_tty);
+  symbol_file_add_main (filename, add_flags);
 
   do_cleanups (cleanups);
   return 1;
diff --git a/gdb/solib.c b/gdb/solib.c
index 5067191c577..29b25d56c7a 100644
--- a/gdb/solib.c
+++ b/gdb/solib.c
@@ -380,21 +380,22 @@ solib_find_1 (char *in_pathname, int *fd, int is_solib)
 /* Return the full pathname of the main executable, or NULL if not
    found.  The returned pathname is malloc'ed and must be freed by
    the caller.  If FD is non-NULL, *FD is set to either -1 or an open
-   file handle for the main executable.
-
-   The search algorithm used is described in solib_find_1's comment
-   above.  */
+   file handle for the main executable.  */
 
 char *
 exec_file_find (char *in_pathname, int *fd)
 {
-  char *result = solib_find_1 (in_pathname, fd, 0);
+  char *result;
+  const char *fskind = effective_target_file_system_kind ();
+
+  if (in_pathname == NULL)
+    return NULL;
 
-  if (result == NULL)
+  if (*gdb_sysroot != '\0' && IS_TARGET_ABSOLUTE_PATH (fskind, in_pathname))
     {
-      const char *fskind = effective_target_file_system_kind ();
+      result = solib_find_1 (in_pathname, fd, 0);
 
-      if (fskind == file_system_kind_dos_based)
+      if (result == NULL && fskind == file_system_kind_dos_based)
 	{
 	  char *new_pathname;
 
@@ -405,6 +406,21 @@ exec_file_find (char *in_pathname, int *fd)
 	  result = solib_find_1 (new_pathname, fd, 0);
 	}
     }
+  else
+    {
+      /* It's possible we don't have a full path, but rather just a
+	 filename.  Some targets, such as HP-UX, don't provide the
+	 full path, sigh.
+
+	 Attempt to qualify the filename against the source path.
+	 (If that fails, we'll just fall back on the original
+	 filename.  Not much more we can do...)  */
+
+      if (!source_full_path_of (in_pathname, &result))
+	result = xstrdup (in_pathname);
+      if (fd != NULL)
+	*fd = -1;
+    }
 
   return result;
 }
diff --git a/gdb/symfile.c b/gdb/symfile.c
index 616fef0f8c2..f524f56b367 100644
--- a/gdb/symfile.c
+++ b/gdb/symfile.c
@@ -85,7 +85,7 @@ int readnow_symbol_files;	/* Read full symbols immediately.  */
 
 static void load_command (char *, int);
 
-static void symbol_file_add_main_1 (const char *args, int from_tty,
+static void symbol_file_add_main_1 (const char *args, symfile_add_flags add_flags,
 				    objfile_flags flags);
 
 static void add_symbol_file_command (char *, int);
@@ -1306,19 +1306,16 @@ symbol_file_add (const char *name, symfile_add_flags add_flags,
    command itself.  */
 
 void
-symbol_file_add_main (const char *args, int from_tty)
+symbol_file_add_main (const char *args, symfile_add_flags add_flags)
 {
-  symbol_file_add_main_1 (args, from_tty, 0);
+  symbol_file_add_main_1 (args, add_flags, 0);
 }
 
 static void
-symbol_file_add_main_1 (const char *args, int from_tty, objfile_flags flags)
+symbol_file_add_main_1 (const char *args, symfile_add_flags add_flags,
+			objfile_flags flags)
 {
-  symfile_add_flags add_flags = (current_inferior ()->symfile_flags
-				 | SYMFILE_MAINLINE);
-
-  if (from_tty)
-    add_flags |= SYMFILE_VERBOSE;
+  add_flags |= current_inferior ()->symfile_flags | SYMFILE_MAINLINE;
 
   symbol_file_add (args, add_flags, NULL, flags);
 
@@ -1655,9 +1652,13 @@ symbol_file_command (char *args, int from_tty)
     {
       char **argv = gdb_buildargv (args);
       objfile_flags flags = OBJF_USERLOADED;
+      symfile_add_flags add_flags = 0;
       struct cleanup *cleanups;
       char *name = NULL;
 
+      if (from_tty)
+	add_flags |= SYMFILE_VERBOSE;
+
       cleanups = make_cleanup_freeargv (argv);
       while (*argv != NULL)
 	{
@@ -1667,7 +1668,7 @@ symbol_file_command (char *args, int from_tty)
 	    error (_("unknown option `%s'"), *argv);
 	  else
 	    {
-	      symbol_file_add_main_1 (*argv, from_tty, flags);
+	      symbol_file_add_main_1 (*argv, add_flags, flags);
 	      name = *argv;
 	    }
 
diff --git a/gdb/symfile.h b/gdb/symfile.h
index cd94d855850..59952cbba23 100644
--- a/gdb/symfile.h
+++ b/gdb/symfile.h
@@ -543,7 +543,8 @@ extern CORE_ADDR overlay_unmapped_address (CORE_ADDR, struct obj_section *);
 extern CORE_ADDR symbol_overlayed_address (CORE_ADDR, struct obj_section *);
 
 /* Load symbols from a file.  */
-extern void symbol_file_add_main (const char *args, int from_tty);
+extern void symbol_file_add_main (const char *args,
+				  symfile_add_flags add_flags);
 
 /* Clear GDB symbol tables.  */
 extern void symbol_file_clear (int from_tty);
diff --git a/gdb/testsuite/ChangeLog b/gdb/testsuite/ChangeLog
index 460e6b9abc3..d0a2bc986ad 100644
--- a/gdb/testsuite/ChangeLog
+++ b/gdb/testsuite/ChangeLog
@@ -1,3 +1,7 @@
+2016-10-25  Luis Machado  <lgustavo@codesourcery.com>
+
+	* gdb.base/exec-invalid-sysroot.exp: New file.
+
 2016-10-24  Jan Kratochvil  <jan.kratochvil@redhat.com>
 
 	* gdb.base/morestack.exp: Try to build it using -fuse-ld=gold first.
diff --git a/gdb/testsuite/gdb.base/exec-invalid-sysroot.exp b/gdb/testsuite/gdb.base/exec-invalid-sysroot.exp
new file mode 100644
index 00000000000..9665b5fc330
--- /dev/null
+++ b/gdb/testsuite/gdb.base/exec-invalid-sysroot.exp
@@ -0,0 +1,70 @@
+#   Copyright 1997-2016 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/>.
+
+# This test exercises PR20569.  GDB would crash when attempting to follow
+# an exec call when it could not resolve the path to the symbol file.
+# This was the case when an invalid sysroot is provided.
+
+standard_testfile foll-exec.c
+
+global binfile
+set binfile [standard_output_file "foll-exec"]
+set testfile2 "execd-prog"
+set srcfile2 ${testfile2}.c
+set binfile2 [standard_output_file ${testfile2}]
+
+set compile_options debug
+
+# build the first test case
+if  { [gdb_compile "${srcdir}/${subdir}/${srcfile2}" "${binfile2}" executable $compile_options] != "" } {
+    untested "could not compile test program ${binfile2}"
+    return -1
+}
+
+if  { [gdb_compile "${srcdir}/${subdir}/${srcfile}" "${binfile}" executable $compile_options] != "" } {
+    untested "could not compile test program ${binfile}"
+    return -1
+}
+
+proc do_exec_sysroot_test {} {
+    global binfile srcfile srcfile2 testfile testfile2
+    global gdb_prompt
+
+    gdb_test_no_output "set sysroot /a/path/that/does/not/exist"
+
+    # Start the program running, and stop at main.
+    #
+    if ![runto_main] then {
+	fail "Couldn't run ${testfile}"
+	return
+    }
+
+    # Verify that the system supports "catch exec".
+    gdb_test "catch exec" "Catchpoint \[0-9\]* \\(exec\\)" "insert exec catchpoint"
+    set test "continue to exec catchpoint"
+    gdb_test_multiple "continue" $test {
+	-re ".*Your system does not support this type\r\nof catchpoint.*$gdb_prompt $" {
+	    unsupported $test
+	    return
+	}
+	-re ".*Could not load symbols for executable.*$gdb_prompt $" {
+	    pass $test
+	}
+    }
+}
+
+# Start with a fresh gdb
+clean_restart $binfile
+do_exec_sysroot_test