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[binutils-gdb] error/internal-error printing local variable during "bt full".


https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=16c3b12f199a7ec99a0b51bd83b66942547bba87

commit 16c3b12f199a7ec99a0b51bd83b66942547bba87
Author: Joel Brobecker <brobecker@adacore.com>
Date:   Mon Nov 23 10:02:50 2015 -0800

    error/internal-error printing local variable during "bt full".
    
    One of our users reported an internal error using the "bt full"
    command. In their situation, reproducing involved the following
    scenario:
    
        (gdb) frame 1
        (gdb) bt full
        #0  0xf7783430 in __kernel_vsyscall ()
        No symbol table info available.
        #1  0xf5550aeb in waitpid () at ../sysdeps/unix/syscall-template.S:81
        No locals.
        [...]
        #6  0x0fe83139 in xxxx (arg=...)
        [...some locals printed, and then...]
        <S17b> =
        [...]/dwarf2loc.c:364: internal-error: dwarf_expr_frame_base: Assertion
        `framefunc != NULL' failed.
    
    As shown above, the error happens while GDB is trying to print the value
    of <S17b>, which is a local string internally generated by the compiler.
    For that, it finds that the array lives in memory, and therefore tries
    to create a struct value for it via:
    
            case DWARF_VALUE_MEMORY:
              {
                CORE_ADDR address = dwarf_expr_fetch_address (ctx, 0);
                [...]
                retval = value_at_lazy (type, address + byte_offset);
    
    Unfortunately for us, TYPE happens to be an array whose bounds
    are dynamic. More precisely, the bounds of our arrays are described
    in the debugging info as being...
    
     <4><2c1985e>: Abbrev Number: 33 (DW_TAG_subrange_type)
        <2c1985f>   DW_AT_type        : <0x2c1989c>
        <2c19863>   DW_AT_lower_bound : <0x2c19835>
        <2c19867>   DW_AT_upper_bound : <0x2c19841>
    
    ... which are references to a pair of local variables. For instance,
    the lower bound is a reference to the following DIE
    
     <3><2c19835>: Abbrev Number: 32 (DW_TAG_variable)
        <2c19836>   DW_AT_name        : [...]
        <2c1983a>   DW_AT_type        : <0x2c198b4>
        <2c1983e>   DW_AT_artificial  : 1
        <2c1983e>   DW_AT_location    : 2 byte block: 91 58         (DW_OP_fbreg: -40)
    
    As a result of the above, value_at_lazy indirectly triggers
    a resolution of TYPE (via value_from_contents_and_address),
    which means a resolution of TYPE's bounds, and as seen in
    the DW_AT_location attribute above for our bounds, computing
    the bound's location requires the frame (its location expression
    uses DW_OP_fbreg).
    
    Unfortunately for us, value_at_lazy does not get passed a frame,
    we've lost the relevant frame when we try to resolve the array's
    bounds. Instead, resolve_dynamic_range gets calls dwarf2_evaluate_property
    with NULL as the frame:
    
        static struct type *
        resolve_dynamic_range (struct type *dyn_range_type,
                               struct property_addr_info *addr_stack)
        {
          [...]
          if (dwarf2_evaluate_property (prop, NULL, addr_stack, &value))
                                              ^^^^
    
    ... which then handles this by using the selected frame instead:
    
        if (frame == NULL && has_stack_frames ())
          frame = get_selected_frame (NULL);
    
    In our case, the selected frame happens to be frame #1, which is
    a frame where we have a minimal amount of debugging info, and in
    particular, no debug info for the function itself. And because of that,
    when we try to determine the frame's base...
    
        static void
        dwarf_expr_frame_base (void *baton, const gdb_byte **start,
                               size_t * length)
        {
          struct dwarf_expr_baton *debaton = (struct dwarf_expr_baton *) baton;
          const struct block *bl = get_frame_block (debaton->frame, NULL);
          [...]
          framefunc = block_linkage_function (bl);
    
    ... framefunc ends up being NULL, which triggers the assert
    in that same function:
    
          gdb_assert (framefunc != NULL);
    
    This patches avoids the issue by temporarily setting the selected_frame
    before printing the locals of each frames.
    
    This patch also adds a small testcase, which reproduces the same
    issue, but with a slightly different outcome:
    
        (gdb) bt full
        #0  0x000000000040049a in opaque_routine ()
        No symbol table info available.
        #1  0x0000000000400532 in main () at wrong_frame_bt_full-main.c:20
                my_table_size = 3
                my_table = <error reading variable my_table (frame address is not available.)>
    
    With this patch, the output becomes:
    
        (gdb) bt full
        [...]
                my_table = {0, 1, 2}
    
    gdb/ChangeLog:
    
            * stack.c (print_frame_local_vars): Temporarily set the selected
            frame to FRAME while printing the frame's local variables.
    
    gdb/testsuite/ChangeLog:
    
            * gdb.base/wrong_frame_bt_full-main.c: New file.
            * gdb.base/wrong_frame_bt_full-opaque.c: New file.
            * gdb.base/wrong_frame_bt_full.exp: New file.

Diff:
---
 gdb/ChangeLog                                      |  5 ++
 gdb/stack.c                                        | 25 ++++++++--
 gdb/testsuite/ChangeLog                            |  6 +++
 gdb/testsuite/gdb.base/wrong_frame_bt_full-main.c  | 34 +++++++++++++
 .../gdb.base/wrong_frame_bt_full-opaque.c          | 22 +++++++++
 gdb/testsuite/gdb.base/wrong_frame_bt_full.exp     | 55 ++++++++++++++++++++++
 6 files changed, 144 insertions(+), 3 deletions(-)

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index ffcac03..d648e56 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,5 +1,10 @@
 2015-11-23  Joel Brobecker  <brobecker@adacore.com>
 
+	* stack.c (print_frame_local_vars): Temporarily set the selected
+	frame to FRAME while printing the frame's local variables.
+
+2015-11-23  Joel Brobecker  <brobecker@adacore.com>
+
 	* amd64-windows-tdep.c (amd64_windows_frame_decode_epilogue):
 	Increment PC in while loop skipping "pop reg" instructions.
 
diff --git a/gdb/stack.c b/gdb/stack.c
index b825bdf..163b72d 100644
--- a/gdb/stack.c
+++ b/gdb/stack.c
@@ -2082,6 +2082,7 @@ print_frame_local_vars (struct frame_info *frame, int num_tabs,
   struct print_variable_and_value_data cb_data;
   const struct block *block;
   CORE_ADDR pc;
+  struct gdb_exception except = exception_none;
 
   if (!get_frame_pc_if_available (frame, &pc))
     {
@@ -2102,9 +2103,27 @@ print_frame_local_vars (struct frame_info *frame, int num_tabs,
   cb_data.stream = stream;
   cb_data.values_printed = 0;
 
-  iterate_over_block_local_vars (block,
-				 do_print_variable_and_value,
-				 &cb_data);
+  /* Temporarily change the selected frame to the given FRAME.
+     This allows routines that rely on the selected frame instead
+     of being given a frame as parameter to use the correct frame.  */
+  select_frame (frame);
+
+  TRY
+    {
+      iterate_over_block_local_vars (block,
+				     do_print_variable_and_value,
+				     &cb_data);
+    }
+  CATCH (ex, RETURN_MASK_ALL)
+    {
+      except = ex;
+    }
+  END_CATCH
+
+  /* Restore the selected frame, and then rethrow if there was a problem.  */
+  select_frame (frame_find_by_id (cb_data.frame_id));
+  if (except.reason < 0)
+    throw_exception (except);
 
   /* do_print_variable_and_value invalidates FRAME.  */
   frame = NULL;
diff --git a/gdb/testsuite/ChangeLog b/gdb/testsuite/ChangeLog
index 6518f14..2c59ad8 100644
--- a/gdb/testsuite/ChangeLog
+++ b/gdb/testsuite/ChangeLog
@@ -1,5 +1,11 @@
 2015-11-23  Joel Brobecker  <brobecker@adacore.com>
 
+	* gdb.base/wrong_frame_bt_full-main.c: New file.
+	* gdb.base/wrong_frame_bt_full-opaque.c: New file.
+	* gdb.base/wrong_frame_bt_full.exp: New file.
+
+2015-11-23  Joel Brobecker  <brobecker@adacore.com>
+
 	* testsuite/gdb.ada/var_rec_arr.exp: Add "ptype a1(1)" test.
 
 2015-11-20  Jose E. Marchesi  <jose.marchesi@oracle.com>
diff --git a/gdb/testsuite/gdb.base/wrong_frame_bt_full-main.c b/gdb/testsuite/gdb.base/wrong_frame_bt_full-main.c
new file mode 100644
index 0000000..73ab34c
--- /dev/null
+++ b/gdb/testsuite/gdb.base/wrong_frame_bt_full-main.c
@@ -0,0 +1,34 @@
+/* Copyright (C) 2015 Free Software Foundation, Inc.
+
+   This file is part of GDB.
+
+   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/>.  */
+
+extern void opaque_routine (void);
+
+int dyn_arr_size = 4;
+
+int
+main (void)
+{
+  int i;
+  int my_table_size = dyn_arr_size - 1;
+  int my_table [my_table_size];
+
+  for (i = 0; i < my_table_size; i++)
+    my_table[i] = i;
+
+  opaque_routine ();
+  return 0;
+}
diff --git a/gdb/testsuite/gdb.base/wrong_frame_bt_full-opaque.c b/gdb/testsuite/gdb.base/wrong_frame_bt_full-opaque.c
new file mode 100644
index 0000000..19b8770
--- /dev/null
+++ b/gdb/testsuite/gdb.base/wrong_frame_bt_full-opaque.c
@@ -0,0 +1,22 @@
+/* Copyright (C) 2015 Free Software Foundation, Inc.
+
+   This file is part of GDB.
+
+   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/>.  */
+
+void
+opaque_routine (void)
+{
+  /* Do nothing.  */
+}
diff --git a/gdb/testsuite/gdb.base/wrong_frame_bt_full.exp b/gdb/testsuite/gdb.base/wrong_frame_bt_full.exp
new file mode 100644
index 0000000..863cc1b
--- /dev/null
+++ b/gdb/testsuite/gdb.base/wrong_frame_bt_full.exp
@@ -0,0 +1,55 @@
+# Copyright (C) 2015 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/>.
+
+# Build wrong_frame_bt_full-main using two C files:
+#   - wrong_frame_bt_full-opaque.c, which needs to be built without
+#     debugging info;
+#   - wrong_frame_bt_full-main.c, which needs to be built with
+#     debugging info.
+# This is why we use gdb_compile instead of relying on he usual call
+# to prepare_for_testing.
+
+set main_testfile wrong_frame_bt_full-main
+set opaque_testfile wrong_frame_bt_full-opaque
+
+if {[gdb_compile "${srcdir}/${subdir}/$opaque_testfile.c" \
+                 $opaque_testfile.o \
+                 object {}] != ""} {
+  untested "failed to compile $opaque_testfile.c"
+  return -1
+}
+
+if {[gdb_compile \
+      [list ${srcdir}/${subdir}/$main_testfile.c $opaque_testfile.o] \
+      [standard_output_file ${main_testfile}] \
+      executable {debug}] != ""} {
+    untested "failed to build $main_testfile"
+    return -1
+}
+
+clean_restart ${main_testfile}
+
+if ![runto opaque_routine] {
+    untested "could not run to opaque_routine"
+    return -1
+}
+
+# Make sure that "bt full" command is capable of displaying MY_TABLE
+# correctly when frame #0 (the frame which does not have any debugging
+# info) is the selected frame.
+
+gdb_test "bt full" \
+         ".*\[\r\n\]+ *my_table = \\{0, 1, 2\\}\[\r\n\]+.*"
+


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