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Binutils with MCST patches
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Joel Brobecker 7d1c9c9b4c crash printing non-local variable from nested subprogram 
We have noticed that GDB would sometimes crash trying to print
from a nested function the value of a variable declared in an
enclosing scope. This appears to be target dependent, although
that correlation might only be fortuitious.  We noticed the issue
on x86_64-darwin, x86-vxworks6 and x86-solaris.  The investigation
was done on Darwin.

This is a new feature that was introduced by:

    commit 63e43d3aed
    Date:   Thu Feb 5 17:00:06 2015 +0100
    DWARF: handle non-local references in nested functions

We can reproduce the problem with one of the testcases that was
added with the patch (gdb.base/nested-subp1.exp), where we have...

    18 int
    19 foo (int i1)
    20 {
    21   int
    22   nested (int i2)
    23   {
    [...]
    27     return i1 * i2; /* STOP */
    28   }

...  After building the example program, and running until line 27,
try printing the value of "i1":

    % gdb gdb.base/nested-subp1
    (gdb) break foo.c:27
    (gdb) run
    Breakpoint 1, nested (i2=2) at /[...]/nested-subp1.c:27
    27          return i1 * i2; /* STOP */
    (gdb) p i1
    [1]    73090 segmentation fault  ../gdb -q gdb.base/nested-subp1

Ooops!

What happens is that, because the reference is non-local, we are trying
to follow the function's static link, which does...

    /* If we don't know how to compute FRAME's base address, don't give up:
       maybe the frame we are looking for is upper in the stace frame.  */
    if (framefunc != NULL
        && SYMBOL_BLOCK_OPS (framefunc)->get_frame_base != NULL
        && (SYMBOL_BLOCK_OPS (framefunc)->get_frame_base (framefunc, frame)
            == upper_frame_base))

... or, in other words, calls the get_frame_base "method" of
framefunc's struct symbol_block_ops data. This resolves to
the block_op_get_frame_base function.

Looking at the function's implementation, we see:

  struct dwarf2_locexpr_baton *dlbaton;
  [...]
  dlbaton = SYMBOL_LOCATION_BATON (framefunc);
  [...]
  result = dwarf2_evaluate_loc_desc (type, frame, start, length,
                                     dlbaton->per_cu);
                                     ^^^^^^^^^^^^^^^

Printing dlbaton->per_cu gives a value that seems fairly bogus for
a memory address (0x60). Because of it, dwarf2_evaluate_loc_desc
then crashes trying to dereference it.

What's different on Darwin compared to Linux is that the function's
frame base is encoded using the following form:

        .byte   0x40    # uleb128 0x40; (DW_AT_frame_base)
        .byte   0x6     # uleb128 0x6; (DW_FORM_data4)

... and so dwarf2_symbol_mark_computed ends up creating
a SYMBOL_LOCATION_BATON as a struct dwarf2_loclist_baton:

  if (attr_form_is_section_offset (attr)
      /* .debug_loc{,.dwo} may not exist at all, or the offset may be outside
         the section.  If so, fall through to the complaint in the
         other branch.  */
      && DW_UNSND (attr) < dwarf2_section_size (objfile, section))
    {
      struct dwarf2_loclist_baton *baton;
      [...]
      SYMBOL_LOCATION_BATON (sym) = baton;

However, if you look more closely at block_op_get_frame_base's
implementation, you'll notice that the function extracts the
symbol's SYMBOL_LOCATION_BATON as a dwarf2_locexpr_baton
(a DWARF _expression_ rather than a _location list_).
That's why we end up decoding the DLBATON improperly, and thus
pass a random dlbaton->per_cu when calling dwarf2_evaluate_loc_desc.

This works on x86_64-linux, because we indeed have the frame base
described using a different form:

        .uleb128 0x40   # (DW_AT_frame_base)
        .uleb128 0x18   # (DW_FORM_exprloc)

This patch fixes the issue by doing what we do for most (if not all)
other such methods: providing one implementation each for loc-list,
and loc-expr. Both implementations are nearly identical, so perhaps
we might later want to improve this. But this patch first tries to
fix the crash first, leaving the design issue for later.

gdb/ChangeLog:

        * dwarf2loc.c (locexpr_get_frame_base): Renames
        block_op_get_frame_base.
        (dwarf2_block_frame_base_locexpr_funcs): Replace reference to
        block_op_get_frame_base by reference to locexpr_get_frame_base.
        (loclist_get_frame_base): New function, near identical copy of
        locexpr_get_frame_base.
        (dwarf2_block_frame_base_loclist_funcs): Replace reference to
        block_op_get_frame_base by reference to loclist_get_frame_base.

Tested on x86_64-darwin (AdaCore testsuite), and x86_64-linux
(official testsuite).
2015-09-20 11:18:49 -07:00
bfd Add --no-dynamic-linker option to ld, for static PIE use 2015-09-20 15:52:27 +09:30
binutils Adds an option to the strings program to specify a separator between the emitted pieces of text. 2015-09-10 09:29:13 +01:00
config Missing parts of fixes for in-tree libiconv 2015-08-24 10:57:03 +01:00
cpu
elfcpp
etc
gas S/390: Fix instruction format of crj*, clrj*, and clgrj*. 2015-09-10 15:26:35 +02:00
gdb crash printing non-local variable from nested subprogram 2015-09-20 11:18:49 -07:00
gold Fix internal error caused by IFUNC patch. 2015-09-07 09:44:11 -07:00
gprof Remove trailing spaces in gprof 2015-08-12 04:43:32 -07:00
include Add --no-dynamic-linker option to ld, for static PIE use 2015-09-20 15:52:27 +09:30
intl Regen intl/configure 2015-08-31 12:53:36 +09:30
ld Add --no-dynamic-linker option to ld, for static PIE use 2015-09-20 15:52:27 +09:30
libdecnumber
libiberty PR gdb/18669 libiberty demangle.test failure: strtod() on sparc-sun-solaris2.9 2015-08-11 09:14:12 +02:00
opcodes S/390: Fix instruction format of crj*, clrj*, and clgrj*. 2015-09-10 15:26:35 +02:00
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ChangeLog Sync config.sub and config.guess with GCC 2015-08-07 07:51:39 -07:00
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README 

		   README for GNU development tools

This directory contains various GNU compilers, assemblers, linkers, 
debuggers, etc., plus their support routines, definitions, and documentation.

If you are receiving this as part of a GDB release, see the file gdb/README.
If with a binutils release, see binutils/README;  if with a libg++ release,
see libg++/README, etc.  That'll give you info about this
package -- supported targets, how to use it, how to report bugs, etc.

It is now possible to automatically configure and build a variety of
tools with one command.  To build all of the tools contained herein,
run the ``configure'' script here, e.g.:

	./configure 
	make

To install them (by default in /usr/local/bin, /usr/local/lib, etc),
then do:
	make install

(If the configure script can't determine your type of computer, give it
the name as an argument, for instance ``./configure sun4''.  You can
use the script ``config.sub'' to test whether a name is recognized; if
it is, config.sub translates it to a triplet specifying CPU, vendor,
and OS.)

If you have more than one compiler on your system, it is often best to
explicitly set CC in the environment before running configure, and to
also set CC when running make.  For example (assuming sh/bash/ksh):

	CC=gcc ./configure
	make

A similar example using csh:

	setenv CC gcc
	./configure
	make

Much of the code and documentation enclosed is copyright by
the Free Software Foundation, Inc.  See the file COPYING or
COPYING.LIB in the various directories, for a description of the
GNU General Public License terms under which you can copy the files.

REPORTING BUGS: Again, see gdb/README, binutils/README, etc., for info
on where and how to report problems.